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Thermal Dynamics

Jarrod McLean

on 18 January 2013

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Transcript of Chemistry

Jarrod McLean, Casey Bigelow, Matt Kortz, Telayna Johnson, and Alixis Grano Energy Changes and Rates of Reaction Chemistry is the study of matter and its transformations, which means thermochemistry is the study of the energy changes that accompany physical or chemical changes in matter. 5.1 Changes in matter and energy Combustion reactions are the most familiar exothermic reactions. The searing heat produced by a burning building is formidable obstacle facing firefighters 5.3 Representing Enthalpy Change As particles move closer to one another in a chemical system, they experience a repulsive force and their kinetic energy is converted into chemical potential energy. If a group of particles have not reached their activation energy, the entirety of their kinetic energy will be converted into potential before they can collide. If the kinetic energy is equal to or greater than the activation energy, they will be able to overcome the repulsion and collide. When the particles are in contact and the chemical bonds are broken, the system is at its highest possible potential energy state. At this point, the particles assume a new configuration called an activated complex, which then lowers to a new energy state which may be higher or lower than the initial state. 6.4 - Collision Theory 6.3 - Rate Laws 6.3 continued -
Half-lives From Chapter Six, Chemical Kinetics, you should have got a basic understanding of what is the overall or average rate of reaction, given change in concentration over time, what the rate of reaction with respect to a specific participating substance and give the rate with respect to another substance in the reaction. You should also know a bit about the initial rate of reaction, given a rate law equation and information about how the concentration is changed. Conclusion When water decomposes, the system gains energy from the surroundings and so the molar enthalpy is reported as a positive quantity to indicate an endothermic change:
H2O(l) -> H2(g) + ½ O2(g) Hdecomp = + 285.8 kJ/mol H2O

The law of conservation of energy implies that the reverse process (combustion of hydrogen) has an equal and opposite energy change.
H2(g) + 1/2 O2(g) -> H2O(l) Hcomb= -285.8 kJ/mol H2 Hydrocarbons such as acetone burn with a readily visible flame. The flame produced by combusting methanol (left) is difficult to see and so more dangerous. Writing Thermochemical Equations with Energy Terms
1.First, write the equation for the combustion of the product given
2.Then obtain the amount of the product,n, from the balanced equation.
3.If the reaction is exothermic, that means that the energy term must be a product.Report the enthalpy change for the reaction by writing it as a product in the thermochemical equation Writing Thermochemical Equations with H Values
1.Write the balanced chemical equation out
2.The obtain the amount of sulfur dioxide,n, from the balanced equation and use the formula H=nHc Molar Enthalpy of Reaction: Hx the energy change associated with the reaction of one mole of a substance (also called molar enthalpy change) Standard Molar Enthalpy of Reaction: Hdegreesx, the energy change associated with the reaction of one mole of a substance at 100 kPa and a specified temperature (usually at 25 degrees Celcius) -Endothermic enthalpy changes are reported as positive values
-Exothermic enthalpy changes are reports as negative values Methanol burns more completely than gasoline, producing lower levels of some pollutants. The technology of methanol-burning vehicles was originally developed for racing cars because methanol burns faster than gasoline. However, its energy content is lower so it takes twice as much methanol as gasoline to drive a given distance. During an exothermic reaction, the enthalpy of the system decreases and heat flows into the surroundings. We observe a temperature increase in the surroundings. During endothermic reaction, heat flows from the surroundings into the chemical system. We observe a temperature decrease in the surroundings. This corresponds to an increase in the enthalpy of the chemical system. Potential Energy Diagram: a graphical representation of the energy transferred during a physical or chemical change The combustion of fuels is always exothermic: heat is released to the surroundings. Enthalpies of combustion are often called heats of combustion and given as absolute values. For example Hcomb(methanol) = 726 kJ/mol Methanol Oxygen is often the reactant given a fractional coefficent in combustion equations because it occurs as a diatomic molecule and the total numbers of oxygen atoms in the products are often odd numbers. Sulfuric Acid Plant 5.4 Hess's Law of Additivity of Reaction Enthalpies Some reactions are too slow to be studied experimentally. Predicting H Using Hess's Law
Based on experimental measurements of enthalpy changes, the Swiss chemist G.H Hess suggested that there is a mathematical relationship amoung a series of reactions leading from a set of reactants to a set of products. This generalization has been tested in many experiments and is now accepted as the law of additivity of reaction enthalpies, also known as Hess's Law. Hess's Law:
The value of the H for any reaction that can be written in steps equals the sum of the values of H for each of the individual steps. Another way to state Hess's Law is: If two or more equations with known enthalpy changes can be added together to form a new "target" equation, then their enthalpy changes may be similarly added together to yield the enthalpy change of the target equation. -If a chemical equation is reversed, then the sign of H changes.
-If the coefficients of a chemical equation are altered by multiplying or dividing by a constant factor, then the H is altered in the same way. Using Hess's Law to Find H:
-Find out the target equation
-Work the equations together, called known equations, and then add them together
-May need to double the equation
-Note: The sign of the enthalpy change in the equation will change, since the equation has been reversed
-Add the reactants, products and enthalpy changes to get a net reaction equation
-APPLY HESS'S LAW: If the known equations can be added together to form the target equation, then their enthalpy changes can be added together
-Note: When manipulating the known equations, you should check the target equation and plan ahead to ensure that the substances end up on the correct sides and in the correct amounts. Electric power generating stations that use coal as a fuel are only 30% to 40% efficient. Coal gasification and combustion of the coal gas provide one alternative to burning coal. Efficiency is improved by using both a combustion turbine and a steam turbine to produce electricity. Multistep Energy Calculations
In practice, energy calculations rarely involved only a single-step calculation of heat or enthalpy change. Several energy calculations might be required, involving a combination of energy change definitions such as:
-Heat Flows, q=mc(triangle)T
-Enthalpy Changes, (triangle)H=n(triangle)Hr
-Hess's Law, (triangle)Htarget={(triangle)Hknown

In these multi-step problems, (triangle)H is often found by using standard molar enthalpies or Hess's law and then equated to the transfer of heat, q. If we known the enthalpy change of a reaction and the quantity of reactant or product, we cna predict how much energy will be absorbed or released. Solving Multistep Enthalpy Problems
-Calculate the energy absorbed per mole. That is, the molar enthalpy of reaction
-Covert to a 100 kg then to an amount in moles and multiplying by the molar enthalpy will give you the required enthalpy change (triangle)H, for the equation 5.5 Standard Enthalpies of Formation H o f = -393.5 kJ/mol Standard Enthalpy of Formation is the quantity of energy associated with the formation of one mole of a substance from its elements in their standard states. Writing Formation Equations
Step 1: Write one mole of product in the state that has been specified.
Step 2: Write the reaction elements in their standard states.
Step 3: Choose equation coefficients for the reactants to give a balances equation yielding one mole of product. H o f for elements : the standard enthalpy of formation of an element already in its standard state is zero. Key equation H = {n H o f (products) - {n H o f (reactants) Graphite is the more stable form of carbon. The formation of diamond requires an increase in potential energy. The production of canola crops are dependent on the use of fertilizers such ammonium nitrate. Coal is an important current source of electrical energy in Ontario but its use has serious environmental consequences. The decomposition of sucrose produces black carbon and water. Enthalpies of combustion of hydrocarbons generally assume production of CO2(g) and H2O(l).The states of these compounds at SATP In a reaction mechanism, in which multiple chemical reactions occur in series, a series of collisions called elementary steps occur, the products of each being used as reactants in the next. In this case, a number of activated complexes are formed. The step reaction with the highest activation energy is therefore the one with the slowest reaction rate (because of the higher energy requirement, it would have a lower fraction of collisions that are effective), and is referred to as the rate-determining step. While the effects of various environmental factors on reaction rate are well-understood, one aspect of chemistry that remains puzzling is why chemicals react as they do. Collision theory is a theory that explains the phenomenon of chemical reaction using a model of constantly moving, colliding particles. A chemical system can be thought of as a large group of atoms, ions, and molecules (collectively referred to as “particles”) in constant, random motion. The particles are held together by the force of their chemical bonds. Particles in a chemical system will frequently collide; if the particles collide at the correct angle, and with enough kinetic energy to overcome the force of the already-existing chemical bonds, then the bonds will break down and the particles will re-arrange themselves. When such a re-arrangement happens, the collision is effective and a chemical change can be said to have occurred. There are two factors which determine whether or not a collision is an effective collision: if the colliding particles have the correct orientation, and if they have sufficient kinetic energy. The rate of reaction in a chemical system is determined by the product of the frequency at which collisions occur, and the fraction of them that are effective. Particles in a chemical system are all moving at different speeds, therefore each particle has a unique kinetic energy. The distribution of kinetic energy is determined by the temperature of the system; a higher-temperature system will contain more particles of higher kinetic energy. The minimum kinetic energy with which particles must collide to undergo an effective collision is referred to as the activation energy. Different environmental factors affect the frequency and fraction of collisions in different ways; an increase in concentration or surface area will increase the frequency with which particles collide. The presence of a catalyst will encourage more effective collisions, increasing the fraction. An increase in temperature will give the particles higher kinetic energy, increasing both the frequency and fraction of collisions. Hess's Law
The definition of Hess's Law is that the value of the H for any reaction that can be written in steps equals the sum of the values of H for each of the individual steps. Hess's Law Report Using Hess's Law to Find H
Example: The standard state of most elements in the periodic table is solid. There are 5 common gaseous elements at SATP that form compounds readily: H ,O ,N ,F , and Cl . There are only two liquid elements at SATP: Hg, and Br . 2 2 2 2 2 2 There is an importance of using the standard enthalpy of formation appropriate to the state of a substance. The standard enthalpy of formation of H20(g) (-241.8 kJ/mol) is different from that of H20(l) (-285.5 kJ/mol). Two key relationships that are applied for multistep energy calculations using standard enthalpies of formation :
1. enthalpy change in the system = heat transferred to/from the surroundings H = q and 2. H = n H f Specific heat capacities may be expressed in various units for convenience. For example, the specific heat capacity of water is 4.18 J/(g . o C) or 4.18 kJ/(kg C) or 4.18 MJ/(Mg C) . . o o Remote controlled model boats are powered by burning methanol or a racing mixture of 80% methanol and 20% nitromethane by mass. 5.6 The Energy Debate Freon gas vaporizers in the refrigerator coil inside a freezer, the physical change absorbs energy. When methane burns in a natural gas oven, energy is released to the surroundings. a) b) a) In a hydroelectric power station, water collected behind a dam is released through a pipe to the turbine. b) Water in a boiler is heated in one of several ways :
-chemical energy from the combustion of fossil fuels in a thermal electric power plant;
-nuclear energy from the fission of uranium in a nuclear power plant.
- direct radiant solar energy reflected from many mirrors onto the boiler in a solar power plant
- geothermal energy from the interior of the Earth in a geothermal power plant. In the fission of U-235, one neutron is absorbed, the nucleus splits, and three more neutrons are produced. Cons of Nuclear Energy:
-the possible release of radioactive materials in a reactor malfunction;
-the difficulty of disposing of the highly toxic radioactive wastes;
-the large capital costs of building nuclear reactors and then decommissioning them at the end of their relatively short lifetime;
unknown health effects of long-term low-level exposure to radiation; and;
-thermal pollution from cooling water. In nuclear reactors, the energy released in nuclear fission is absorbed by a primary coolant, which then transfers the energy to a secondary coolant. The energy from the secondary coolant is used in a turbine or engine to generate electrical energy, A typical reactor consists of five components:fuel,moderator,coolant,control rods, and shielding. All of these become radioactive, to some degree, and pose a disposal challenge Water falling in Niagara and nuclear fission in a reactor are both examples of systems in which the amount of stored potential energy decreases and is converted into kinetic energy. Radioactive material, carried by the wind, spread for thousands of kilometers. The element iodine reaches a maximum concentration in the thyroid gland. To reduce the effects of radioactive iodine from fallout, children in several countries were given tablets containing non-radioactive iodine. This iodine would concentrate in the thyroid, so any ingested radio iodine would not stay in the body but be excreted. large tanks of water provide safe short-term storage of nuclear waste. Potential Energy
When a kilogram of water (1 L) flows over Niagara Falls, it loses roughly 1kJ of gravitational potential energy, some fraction of which may be converted into hydroelectricity. When a kilogram of gasoline burns, it releases about 4 x 10 kJ of energy. When a kilogram of uranium in a nuclear reactor undergoes fission, it releases about 1 x 10 kJ of energy. Pros of Nuclear Energy
Has low uranium fuel costs, including transportation;
-causes very little air pollution, such as greenhouse and acid gases; and
reduces our dependence on fossil fuels for electricity generation, allowing those materials to be used for other purposes.
Firstly it is important to understand that a chemical system is a set of reactants and products under study, usually represented by a chemical equation. An exothermic reaction releases thermal energy as heat flows out of the system. Hess's law is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician who published it in 1840. The law states that the total enthalpy change during the complete course of a reaction is the same whether the reaction is made in one step or in several steps.

Hess's law is now understood as an expression of the principle of conservation of energy, also expressed in the first law of thermodynamics, and the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state (i.e. enthalpy is a state function). It applies to the special case of paths consisting of chemical reactions (or changes of state) at constant temperature and pressure. Hess's law can be used to determine the overall energy required for a chemical reaction, when it can be divided into synthetic steps that are individually easier to characterize. This affords the compilation of standard enthalpies of formation, that may be used as a basis to design complex syntheses. What is Energy Changes and Rates of Reaction?
Thermochemistry is the study of the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the system's energy exchange with its surroundings. Thermochemistry is useful in predicting reactant and product quantities throughout the course of a given reaction. In combination with entropy determinations, it is also used to predict whether a reaction is spontaneous or non-spontaneous, favorable or unfavorable. A main reaction in the Sun is when four hydrogen atoms fuse to produce one helium atom 4 H+2 e --> He 1 1 0 1 - 4 2 An endothermic reaction absorbs thermal energy as heat flows into the system.While less exciting than exothermic reactions endothermic reactions are still very useful in day to day life, a good example being a medical cold pack. Calorimetry is the technological process of measuring energy changes in a chemical system, a calorimeter is used to isolate the reaction taking place so that the energy transferred can be more accurately measured. Specific heat capacity is a specific quantity of heat required to raise the temperature of a unit mass of a substance 1 degree Celsius. 5.2 Molar Enthalpies Molar enthalpy (Hx) is the enthalpy change associated with a physical, chemical or nuclear change involving one mole of substance for calculation purposes. A good way to examine molar enthalpy is to look a physical change, such as the vaporization of water. It is not enough to simply know THAT a certain factor affects the rate at which a reaction proceeds; in order for a chemist or engineer to effectively make the most of their reaction rate, they must understand HOW reaction rate changes based on environment, thoroughly and quantitatively. Rate laws create a mathematical relationship between the concentrations of various entities in a reaction and how the affect the reaction rate. There is no real way to theoretically calculate a rate law; instead, we must work backwards from empirical evidence collected through experimentation. Data suggest that the rate of a reaction is exponentially proportional to the product of the concentrations of the reactants. That's a bit of a mouthful, but can be expressed by this generalized equation:

r = k[X]^a * [Y]^b

Where r is the reaction rate, [X] and [Y] are the concentrations of the reactants, and k is a constant unique to that reaction, at specific original concentrations, temperature, and pressure. The values of a and b in the generalized equation represent the orders of reaction in respect to reactants X and Y, respectively. If the concentration of X has a linear relationship with reaction rate, the order of reaction for X (represented by a) is 1. If the relationship is quadratic, a = 2, if cubic, a = 3, etc. The overall order of reaction is the sum of all exponents present in the rate law. The values of the exponents are calculated experimentally, in which the initial concentration of a reactant will be changed while the rest of the system and environment remains constant. By observing the effect of these changes on rate, we can calculate the order of reaction for each reactant, one-by-one. For example, in a reaction of bromate and bisulfite, a doubling of the concentration of bromate may cause a doubling in reaction rate. This means that the reaction is first-order in regards to bromate, and the exponent attached to [BrO3-] would be 1. A doubling in the concentration of bisulfite may lead to a quadrupling in reaction rate, implying a second-order relationship, making the exponent attached to [HSO3-] be 2. Once reaction orders have been determined, it is possible to calculate the rate constant of a chemical reaction. By substituting in collected data, k can be isolated in the generalized equation, giving a complete rate law. As the reactants are consumed in a chemical reaction, their concentrations will obviously decrease. This decrease in concentration leads to a decrease in reaction rate, as we have seen in our rate law equation; therefore, a chemical reaction slows down as it proceeds. Empirical evidence has given a rate law for the half-life of any first-order reaction, which can be manipulated using calculus to yield a more workable equation:

ln 2 = k*t1/2

where k is the rate constant and t1/2 is the half-life of the reactant. 6.5 - Explaining
and Applying A catalyst is one of the more mysterious factors affecting reaction rate. Catalysts may be homogeneous, when they are in the same state of matter as the reactants, or heterogeneous, in which case the catalyst and reactants are in a different state. A catalyst is thought to provide an “alternate path” for the moving particles to follow in their collision, providing a lower activation energy but an identical product. This lower activation energy results in a higher fraction of effective collisions. When a reaction mechanism is analyzed, the catalyst will always be seen to be used up at one point, but will have regenerated by the time the mechanism is finished. H2O(Liquid)+40.8KJ=H2O(Gas aka water vapor) From this we can conclude that the molar enthalpy of vaporization of water is 40.8 KJ There are three simplifying assumptions often used in calorimetry.
1. No heat is transferred between the calorimeter and the outside environment.
2. Any heat absorbed or released by the calorimeter materials, such as the container is negligible.
3. Diluted aquesous solutions are assumed to have the same density and heat capacity of water. From Chapter Five, Thermochemistry, you should have got a basic understanding of
-how much heat is transferred to a known mass of matter, for a given temperature change
-what the enthalpy change for a change in state, given the mass and molar enthalpy is
-what molar enthalpy change is taking place in a calorimeter, given the mass of the system and the solution, and the temperature change
-the thermochemical equation (including the energy term) for a given reaction
-the thermochemical equation (including the enthalpy change, H) for a given reaction Thermochemistry Experiment Chemical Kinetics Videos That Relate To... Thermochemistry Chemical Kinetics Nuclear Fission Report Nuclear fission is a nuclear reaction in which a heavy nucleus (such as uranium) splits into two lighter nuclei (and possible some other radioactive particles as well). Controlled fission occurs when a neutrino bombards the nucleus of an atom, breaking it into two smaller, similarly-sized nuclei. Each newly freed neutron can go on to cause two separate reactions, each of which can cause at least two more. A single impact can jumpstart a chain reaction, driving the release of still more energy. --> If about 200 marbles were lying on a flat surface, all jumbled together, and roughly forming a circle and someone took another marbles and threw it at them, they would fly all around in different directions and groups.That is exactly what happens in nuclear fission. The filled circle is like an atom's nucleus. The marble being thrown is like a "neutron bullet". The only differences are that the marbles are protons and neutrons and the protons and neutrons aren't in a filled circle, but in the actual atom are in the shape of a sphere. In the fission of U-235, one neutron is absorbed, the nucleus splits, and three more neutrons are produced. How Nuclear Fission Works
Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously. The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation. U235 + n fission + 2 or 3 n + 200 MeV

If each neutron releases two more neutrons, then the number of fissions doubles each generation. In that case, in 10 generations there are 1,024 fissions and in 80 generations about 6 x 10 23 (a mole) fissions. Energy Released From Each Fission

165 MeV
7 MeV
6 MeV
7 MeV
6 MeV
9 MeV

200 MeV

~ kinetic energy of fission products
~ gamma rays
~ kinetic energy of the neutrons
~ energy from fission products
~ gamma rays from fission products
~ anti-neutrinos from fission products

1 MeV (million electron volts) = 1.609 x 10 -13 joules To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this ratio is less than one then the reaction will die out; if it is greater than one it will grow uncontrolled (an atomic explosion). References:
Rossenfeld, C., & Grifith, C. (n.d.). Nuclear Fission: Basics | Nuclear Fission | Science | atomicarchive.com. atomicarchive.com: Exploring the History, Science, and Consequences of the Atomic Bomb. Retrieved January 17, 2013, from http://www.atomicarchive.com/Fission/Fission1.shtml
D, S., & D, L. (n.d.). Basic Nuclear Fission. ThinkQuest : Library. Retrieved January 17, 2013, from http://library.thinkquest.org/17940/texts/fission/fission.html One of the most commonly-known applications of our knowledge of reaction rates and half-lives is the process of carbon dating. Carbon dating is a process by which the time elapsed since the death of a sample of organic matter can be calculated. Remains such as ancient tools, fossils, and mummies can all have their age calculated through carbon dating, making the process a very useful tool for archaeologists, anthropologists, and historians all around the world.

Carbon dating is more accurately referred to as “radiocarbon dating”, as the isotope of carbon that is most useful in the dating process is the radioactive carbon-14 isotope. As a radioisotope, C-14 naturally undergoes nuclear decay, meaning its nucleus will, over time, break down into multiple other, smaller nuclei. C-14 is a very rare isotope; the two stable isotopes of carbon, C-12 and C-13, which do not undergo radioactive decay, are infinitely more common, with C-14 representing only about one in every trillion carbon atoms.

Carbon-14 has a half-life of about 5730 years. While this may seem like a large figure, it is relatively low when compared with radioisotopes of other elements. Because of C-14's quick dissipation, along with its low initial quantity on earth, one could expect C-14 to be so trace as to be almost non-existent by now. However, C-14 is being constantly produced by cosmic rays. These cosmic rays bombard the earth's atmosphere and create high-energy neutrons, which collide with the non-radioactive nitrogen isotope N-14. Huge amounts of cosmic rays enter the atmosphere every day, and N-14 is very abundant in air, so these collisions happen very frequently. The energy of the neutron causes a nuclear reaction, ejecting a proton from the N-14 nucleus. With one proton lost but one neutron gained, the N-14 atom has become a carbon atom, albeit one retaining the nitrogen's mass of 14 amu.

When C-14 is formed, it can bond with oxygen in the air to form carbon dioxide. It is through this bond that C-14 enters the organic materials that will someday be carbon dated. Carbon dioxide is absorbed by plant life through the photosynthesis process, so small amounts of this carbon dioxide will be built on C-14. Once the C-14 has been absorbed by plant matter and introduced into the biosphere, it can work its way throughout the food chain into the bodies of almost all living things. Plants containing C-14 are eaten by primary consumers, which are themselves consumed by secondary consumers, up to the point where every organism on earth contains a small amount of C-14. Most of the C-14 on earth is contained in the oceans, where the carbon dioxide reacts with water to form carbonic acid. Living things are always taking in more carbon dioxide at a relatively constant rate, so we can assume the concentration of C-14 in an organism to be more or less constant in its lifetime.

When a historical sample of once-living material is found, scientists are capable of analyzing the ratio of C-14 and stable carbon to determine its age. When organic matter dies, it is no longer undergoing cellular respiration and is no longer consuming other living things or producing its own energy, so it is no longer exchanging carbon with the environment around it. As a result, the carbon it contains will begin to decay, if it can. C-12 and C-13 do not decay, so they will remain at a fixed level as long as the organism is preserved. C-14, on the other hand, will decay because it is radioactive. Using the equilibrium of C-14 and stable carbon in a living thing, it is possible to calculate the C-14 it would have contained at death, and from that calculate the C-14 it has lost since then. Using C-14's half-life of 5730 years, it is simple to calculate the time elapsed using the amount of C-14 that has decayed and the amount that the organic matter had to start with. The formula used to calculate the time since death is:

t = [ ln (Nf/No) / (-0.693) ] * t1/2

Where t is the time elapsed, Nf/No is the ratio of C-14 in the sample to C-14 it would have contained while living, and t1/2 is the half-life of C-14 (5730 years). This formula can be used to calculate the age of samples up to fifty to sixty thousand years old. After this point, the amount of C-14 in a sample becomes negligible.

Carbon dating was developed by Willard Libby beginning in 1949. After the events of the second world war, when the power and scope of nuclear phenomena was becoming more and more apparent, he proposed that radioactive decay, assuming it occurred at a steady rate, could be used to calculate the age of organic materials such as wood, charcoal, organic sediments, and plant and animal remains. After years of work and development, he was able to successfully identify the ages of a number of wood samples, and received the Nobel Prize for chemistry in 1960.

Despite how useful carbon dating has been for many, it is not a perfect process. It operates on a number of assumptions, chiefly amongst them that the C-14 concentration is constant in the atmosphere and all living things. While this is not much of a stretch, considering that the atmosphere and biosphere exchange carbon constantly and in a relatively predictable manner, there is still a margin of error that must be accepted, as it impossible for the system to be at perfect equilibrium at all times. Another flaw in the system is the fact that the C-14 to C-12 ratio has probably not been totally constant at all periods in history; changes to the earth over the years maybe have increased or decreased the relative levels of C-14. Factors such as an animal's diet or digestive system may affect the amount of C-14 it consumes. Carbon dating has also been hypothesized to be unreliable for samples created after the 1940s, thanks nuclear detonations and power generation which may have altered the equilibrium of C-14.

Carbon dating may not be perfect, but it is an immensely useful application of chemical concepts that allows information to be collected in such a way that was little more than a daydream only a century ago. Carbon dating has progressed our knowledge of science and history, and thanks to the work of Willard Libby and his team, mankind's understanding of the world around him has grown dramatically. Carbon Dating Report Rate laws can be used to analyze both chemical and nuclear reactions. Nuclear decay is an example of a first-order reaction, meaning the rate at which a radioisotope breaks down into new nuclei varies linearly with the initial concentration of radioactive material. Because radioactive decay is first-order and so predictable, it is often easy to calculate the half-life of a substance; half-life refers to the time for half the nuclei in a radioactive sample to decay. A first-order chemical system also has a half-life, referring to the time for half of the reactants in the system to be consumed. Each radioisotope in existence has a unique half-life. Half-lives of chemicals are used to calculate how long a chemical may last in the human body. For instance, when cadmium from cigarette is first inhaled, it is very toxic, but its concentration will steadily decrease. The half-life of this substance in the bloodstream can be used to determine how long it will take for the cadmium to reach safe levels. The half-life of carbon-14 (approximately 5730 years) is used in the process of carbon dating to determine the time elapsed since a tissue died using the amount of C-14 that has decayed. The chemical nature of a substance can determine the the strength of its chemical bonds. A chemical which naturally forms stronger bonds will be more difficult to break apart, therefore requiring a higher activation energy for effective collisions. Because of this, the chemical nature of a reactant is often one of the most important factors that determines the rate at which it will react. Chemical geometry can also determine reaction rate. A chemical whose geometry requires collisions to occur at a very specific angle in order to break chemical bonds and be effective will naturally have less frequent effective collisions than a less picky substance, and therefore react more slowly. The concentration of a gas or liquid increased the number of particles contained in a unit of volume; these particles in close quarters will naturally collide more frequently and produce a faster reaction rate than particles who are more spread apart. In a heterogeneous reaction (in which two or more reactants are in different states of matter), the surface area of the reactants can make a huge difference in reaction rate. A higher surface area simply implies that the reacting substances are in contact in more points in space than they would be if surface area was lower; because the particles are touching in more places, they will collide more frequently and yield a faster reaction. Temperature yields one of the most dramatic effects on reaction rate; a ten-degree increase in temperature can often double the rate at which a reaction occurs. This is because temperature increase affects both of the factors determining reaction rate: frequency of collisions, and fraction of effective collisions. Introducing heat to a system basically excites the particles, causing them to move around faster. Because they are moving faster, it logically follows that collisions would occur more frequently. However, the increased speed also yields an increase in kinetic energy distribution, meaning that more particles have a higher kinetic energy. More high-energy particles means more collisions will be able to break the activation energy barrier, increasing the fraction of collisions which are effective. The Ballard fuel cell uses a platinum catalyst to speed the dissociation reaction of hydrogen gas and increase electron flow. When starting a campfire, it is common to use kindling with higher surface area to increase the rate of the wood's combustion. Heat will increase the rate at which copper(II) carbonate (pictured) decomposes into copper(II) oxide and carbon dioxide gas The structure of Carbon-14 C-14 is propagated by
the carbon cycle Formation of C-14 in the stratosphere C-14 in the atmosphere Brain, M. (2000, October 03). How carbon-14 dating works. Retrieved from http://science.howstuffworks.com/environmental/earth/geology/carbon -14.htm Nave, R. (1999). Carbon dating. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html NDT Resource Center. (2010, October 28). Carbon-14 dating. Retrieved from http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/carbondating.htm 6.1 Rate of Reacion Defined as; the speed at which a chemical change occurs, generally expressed as change in concentration per unit time. Average reaction rate (r) = Change in concentration ( c) Elapsed time ( t) _______________ Chemical kinetics is the study of of ways to make chemical reactions go faster or slower. This research begins in laboratories, where reactions can be precisely monitored and concentrations of reactants and products can be manipulated. Blue: Red: Green: Lines drawn at tangent to curve Secant During the course of a reaction, the amount of reactant in the reaction will decrease, while the amount of product will increase. If we graph the consumption of reactant against time, we are able to visualize how quickly the reactant is being used. Using our graph, we are able to determine the average rate of reaction between two points on the graph by calculating the slope of the secant, or line connecting our two points.
To discover the instantaneous rate of reaction (speed at which the reaction proceeded at a particular point in time), we may draw a line at a tangent to the curve, and calculate that line's slope. Measuring Reaction Rates Gas-producing reactions Reactions that
involve ions Reactions that
change colour Gas produced can be collected, and it's volume and/or pressure taken as the reaction proceeds. The faster the reaction, the greater the ghange in volume or pressure in the same time interval. As some reactions proceed, charged ions may be produced. The conductivity of the solution can be measured, with the conductivity increasing as the reaction continues. Some reactions, especially those in solution, will produce a colour change. A spectrophotometer can be used to precisely measure the intervals of colour intensity as the reaction continues. 6.2 Factors Affecting Reaction Rate There are five main factors which control the speed of a chemical reaction; Chemical nature of reactants Concentration of reactants All elements react differently to various stresses, and in various forms. Elements in the same group in the periodic table tend to react similarly, but at different rates. As well, certain metals that react similarly under one condition (such as zinc, iron, and lead all reacting with hydrochloric acid to produce hydrogen gas) may react completely differently after various stresses are added. The reactivity of common metals has been categorized under the activity series. However, the reasons for these reactions, as well as corrosion, become further discussed in Section 5. Concentrated chemicals can play large roles in our lives. For example, while strong acetic acid is highly corrosive, if it is at a low concentration, it can be ingested. Because the reactants are available in greater concentration, it will cause their reaction to proceed more quickly. Temperature As temperatures are increased, molecules in reactions will begin to move more quickly, making it more likely that they will collide, and a reaction will take place. Temperature can dramatically affect reactions; around SATP, a 10 degree rise in temperature can double or triple the rate of chemical reactions.
Conversely, lower temperatures will slow rates of reaction. This is particularly important in food storage, and is utilized by some animals to conserve energy. Surface Area The increase in surface area of reactants will proportionally raise the rate of reaction. This is because the reaction occurs at the interface of the two different phases in a heterogeneous mixture. The more available surface area, the quicker these two interfaces are able to meet. Presence of a Catalyst A catalyst is a substance that alters the rate of a chemical reaction without itself being permanently changed. Catalysts are currently a hot topic of scientific research, as their processes are not completely known; most catalysts have been discovered accidentally.
There are many catalysts that occur naturally in our body, helping to digest food, and run the various reactions that keep our bodies working. These catalysts are proteins in living cells, known as enzymes. Commonly known enzymes include amylase, found in saliva, and lactase, responsible for helping to digest milk products. Cryopreservation Report References Cryopreservation is a process where biological cells and tissues are cooled to extreme temperatures (in artificial processes, −196 °C, the boiling point of liquid nitrogen) in order to preserve them. By lowering the temperature enough, the biological reactions in the cells are slowed to a point where the cell can be frozen in time nearly indefinitely. Cryopreservation exists both as a natural function in animals, and is increasingly becoming used in our society to store human tissues. In nature, cryopreservation exists as a mechanism to help animals survive extreme temperatures, as well as preserve energy. This process is found in certain amphibians, reptiles, and microscopic multi-cellular organisms.
These animals are able to preserve themselves by releasing natural cryoprotectants. When the organism detects a negative shift in temperature, the organism will release a number of chemicals into their blood stream, such as glucose and urea. At the same time, some water will be drawn towards the center of the organism. In doing this, the amount of ice crystals that form inside of the organism is limited. Because there are no ice crystals to burst cells, the organisms are able to "rethaw" when weather gets warmer.
Organisms that are able to preserve themselves in frigid temperatures include several species of frogs, salamanders, turtles, and the microorganism Tardigrada. As well as these animals, many plants are able to slow or stop their life processes during cold winter months, and continue their growth during warmer seasons. Georgia Reproductive Specialists. (2007). Human embryo cryopreservation. Retrieved from http://www.ivf.com/cryo.html Storey, J., & Storey, K. (2012). Freeze tolerance. Retrieved from http://www.naturenorth.com/winter/frozen/frozen3.html Gregory, A. (2000, October 11). Freezing for the future. Retrieved from http://www.research.uky.edu/odyssey/fall00/freezing.html To freeze a tissue or cell sample, great care must be taken. Normally, when cells are frozen, water will leach out of them, and leave behind ice crystals. After freezing and thawing, cells have a large chance of being burst from the ice crystals, or may become dehydrated and die.
To avoid this, cryobiologists add a cryoprotectant; a sort of anti freeze. This anti freeze is typically made of glycols and other chemicals that only start to freeze at low temperatures. After joining the biological cell, the anti freeze will help prevent ice crystals from forming by creating a syrupy amorphous ice. This syrup will slow the freezing process, helping to stop the formation of ice crystals and keep the cell hydrated. Currently, cryopreservation is largely used in the reproductive area of health. Sperm, eggs, as well as embryos can all be frozen and stored for future family planning.
As well as sex cells, blood can also be frozen. This makes access to life saving blood transfusions much easier for those needed surgeries or other medical procedures. With current technology, there are some barriers to the use of cryopreservation. Most notably, large samples of tissues, or full organs, cannot be frozen and regenerated.The amount of ice crystals that form in the delicate structures is too great, and the sample is destroyed. Even with smaller samples, such as freezing sperm, there are significant amounts of cell deaths. This can be combated by vitrification, the process which turned the cell waters to a syrupy amorphous ice, rather than solid ice. However, even this freezing process itself can be problematic, as the preservation chemicals used can be toxic to the cell. In the future, scientists predict that there may be nanobots, able to perform microscopic brain surgery and fix damaged cells. Cryopreservation remains a developing field of science. As the barriers to freezing large cell masses are overcome, there are many exciting applications that cryopreservation offers. If freezing technology is improved to further reduce or get rid of ice crystals formed, it may be possible to freeze whole organs, and use them in organ transplanting and donation. Even further speculated is the ability to freeze your brain after death, and continue your life in the future. Ambitious scientists predict that once regeneration is perfected, the brain can be frozen, revived, and either implanted or grown a new body. Certainly, the prospects for this remain in the realm of science fiction, but improving technologies bring limitless potential. Calorimetry is the act of measuring the heat of chemical reactions or physical changes, or the science of making such measurements. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat and the Greek word (metron), meaning measure. Calorimetry Report The calorimeters shown here can determine the heat of a solution reaction at constant (atmospheric) pressure. The calorimeter is a double styrofoam cup fitted with a plastic top in which there is a hole for a thermometer.

Calorimetry belongs to the most important experimental techniques. It is the only experimental method allowing for direct measurements of various physical and chemical processes and reactions. When appropriate model is used, analysis of results on molecular level is possible. Sources:
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