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INTRODUCTION TO CHEMISTRY
Transcript of INTRODUCTION TO CHEMISTRY
SCHEME OF THE BOOK
MIXTURES OF TWO OR MORE
2 PHASES OR MORE
(WE CAN SEE THE
SHAPE VOLUME PARTICLES COMPRESSIBILITY
DEFINITE DEFINITE TIGHTLY PACKED VERY SLIGHT
SHAPE VOLUME PARTICLES COMPRESSIBILITY
INDEFINITE DEFINITE MOBILE SLIGHT
SHAPE VOLUME PARTICLES COMPRESSIBILITY
INDEFINITE INDEFINITE INDEPENDENT HIGH
Measuring Mass and Volume
The standard unit for mass in the metric system is the kilogram. In chemistry we often use the gram instead, as we tend to work in smaller quantities
Volume is the amount of space occupied by matter
The standard unit for volume is the cubic meter. In chemistry we usually use the volume unit of the liter or the milliliter
Measurement of Temperature
There are three commonly used temperature scales: Farenheit, Celsius, and Kelvin.
We can convert among the temperature scales by using mathematical formulas:
K= ºC + 273.15
ºF = (1.8 · ºC) + 32
ºC = (ºF - 32 ) / 1.8
The density of a substance is the amount of matter (mass) in a given volume of a substance:
d = mass/volume = g/mL or g/cm^3
Specific gravity is the ratio of the density of a substance to the density of another reference substance (usually water)
unit1 x conversion factor = unit2
Element: fundamental or elementary substance that cannot be unbroken down by chemical means to simpler substances.
Atom: smallest particle of an element that can enter into a chemical reaction
Each element has also an abbreviation; these are called
Capitalize only the first letter, and use lowercase second letter if needed.
Ex: Aluminium (Al) , Gold (Au) , Boron (B)
are solids (except mercury). They have high luster, are good conductors of heat and electricity, are malleable, and are ductile.
Metals have tendency to combine with each other to form compounds. Many metals also combine with nonmetals to form compounds such as metallic chlorides, oxides, and sulfides.
are not lustrous, have relatively low melting points and densities, and are generally poor conductors of heat and electricity.
Nonmetals combine with one another to form molecular compounds such as carbon dioxide, methane, butane.
have properties that are intermediate between those of metals and those of nonmetals
Some elements exist in nature as diatomic molecules, we find always an of that element with another atom of the same element.
Compound is a distinct substance that contains two or more elements chemically combined in a definite proportion by mass. They can be decomposed chemically into simpler substances.
is the smallest uncharged individual unit of a compound.
is a posetively charged atom or group of atoms. An
is held together by attraction of forces that exist between positively and negatively charged ions.
A positevily charged ion is called
; a negatively charged ion is called an
A chemical formula shows the symbols and the ratio of atoms of the elements in a compound.
The formula of a compound contains the symbols of all the elements in the compound
When the formula contains one atom of an element, the symbol of that element represents that one atom. The number 1 is not used as a subscript to indicate one atom of an element
When the formula contains more than one atom of an element, the number of atoms is indicated by a subscript written to the right of the symbol of that atom.
When the formula contains more than a group of atoms that occurs as a unit, parenthesis are placed around the group, and the number of units of the group is indicated by a suscript placed to the right of the parentheses.
Formulas show only the number and kind of each atom contained in the compound; the y do not show the arrangement of the atoms in the compound or how they are chemically bonded to one another.
Inherit characteristics of a substance that can be determined without altering its composition; they are associated with its physical existence.
Ex: solid, liquid, melting point, density ...
The ability of a substance to form new substances, either by reaction with other substances or by decomposition.
No two substances have identical physical and chemical properties.
Changes in physical properties such as size, shape, and density or changes in the state of matter without an accompanying change in composition
No new substances are formed in these physical changes
New substances are formed in chemical changes. They have different properties and composition from the original material in any way. The new substances need not resemble the original material in any way
Physical change usually accompanies a chemical change.
Chemical equations are a shorthand method for expressing chemical changes.
The starting substances are called reactants, and the substances produced are called the products
The law of conservation of mass states that no change is observed in the total mass of the substances involved in a chemical change.
Ex: If we have 100 grams of reactant we will have 100 grams of product.
mass of reactant = mass of product
Energy is the capacity of matter to do work.
Is stored energy, or energy that an object possesses due to its relative position.
Is energy that matter possesses due to its motion. When the water behind the dam is released and allowed to flow, its potential energy is changed into kinetic energy, which can be used to drive generators and produce electricity. Moving bodies possesses kinetic energy.
Energy can be converted from one form to another form. Some kinds of energy can be converted to other forms easily and efficiently
4.184 J = 1 cal
Is the quantity of heat energy required to change the temperature of 1 gram of water by 1ºC, usually measured from 14.5ºC to 15.5ºC
of a substance is the quantity of heat (lost or gained) required to change the temperature of 1 g of that substance by 1ºC.
(mass of substance)(specific heat of substance)(difference t) = heat
An energy transformation occurs whenever a chemical change occurs. If energy is absorbed during the change, the products will have more chemical change, the products will have less chemical potential energy than the reactants
The law of conservation of energy says that energy can be neither created nor destroyed, though it can be transformed from one form to another.
Elements are composed of minute, indivisible particles called atoms.
*atoms are composed of subatomic particles*
Atoms of the same element are alike in mass and size.
*not all the atoms of a specific element have the same mass*
Atoms of different elements have different masses and sizes.
Chemical compounds are formed by the union of two or more atoms of different elements.
Atoms combine to form compounds in simple numerical ratios, such as one to one, one to two, two to three, and so on.
Atoms of two elements may combine in different ratios to form more than one compound
*atoms, under special circumstances, can be decomposed*
Dalton's Model of the Atom
Law of definite composition
: a compound always contains two or more elements chemically combined in a definite proportion by mass
Law of multiple proportions
: atoms of two or more elements may combine in different ratios to produce more than one compound
These laws state that:
The composition of a particular substance will always be the same no matter what its origin of how it is formed
the composition of different compounds formed from the same elements will always be unique
The electron (e-) is a particle with a negative electrical charge (-1) and a mass of 9.110 x 10 ^-28 g.
The proton (p) is a particle with actual mass of 1.673 x 10^-24 g. It's relative charge (+1) is equal in magnitude
The neutron (n) has neither a positive nor a negative charge and has an actual mass (1.675 x 10^-24) wich is only very slightly grater than that of a proton.
After Rutherford experiment it was stated that each atom consists of a nucleus surrounded by electrons. The nucleus contains protons and neutrons but does not contain electrons.
In a neutral atom the positive charge of the nucleus (due to protons) is exactly offset by the negative electrons.
A neutral atom contains exactly the same number of protons and electrons.
of a number is the number of protons in the nucleus. The atomic number determines the identity of an atom
General Arrangement of Subatomic Particles
Atoms of an element having the same atomic number but different atomic masses are called
of that element.
----> Mass number (sum of protons and neutrons in the nucleus)
----> Symbol of element
----> Atomic number (number of protons in the nucleus)
ISOTOPES OF AN ELEMENT AND ATOMIC MASS
It is not practical to compare the actual masses of atoms expressed in grams; therefore, a table of relative atomic masses using atomic mass units was devised. The carbon isotope having six protons and six neutrons and designated carbon-12 was chosen as the standard for atomic masses. This reference isotope was assigned a value of exactly 12 atomic mass units (amu). Thus,
1 atomic mass
is defined as equal to 1/12 of the mass of a carbon-12 atom. The actual mass of a carbon-12 atom is 1.9927 x 10^-23 g, and that of one atomic mass unit is
1.6606 X 10^-24 g
The atomic mass of an element is the average relative mass of the isotopes of that element compared to the atomic mass of carbon-12 (exactly 12.000 ... amu)
Mass number - atomic number = number of neutrons
Cation: atom that has lost one or more electrons (positive)
Cations are named the same as their parent atoms Ex: K potassium --> K+ potassium ion
Anions: atom that has gained one or more electrons (negative)
Anions are named differently from cations. To name and anion consisting of only one element, use the stem of the parent element name and change the ending to -ide.
Ex: Cl Chlorine --> Cl- Chloride ion
Most often ions are formed when metals combine with nonmetals.
The charge on an ion can often be predicted from the position of the element on the periodic table. Groupe 1A are 1+, Groupe 2A are 2+, metals in Groupe 3A are 3+.
The elements in the lower center part of the table are called transition metals. These elements tend to form cations with various positive charges. There is no way to predict the charges on these cations. All metals loose electrons to form positive ions. In contrast, the nonmetals form anions by gaining electrons. Group 7A form 1-, The nonmetals from Groupe 6A are 2-.
Elements and ions
Compounds that are composed of ions are called ionic compounds, they will conduct electricity when dissolved in water. These compounds have a net charge of zero.
RULES FOR WRITING FORMULAS WITH IONIC COMPOUNDS
Write the formula for the metal ion followed by the formula for the nonmetal ion.
Combine the smallest numbers of each ion needed to give the charge sum equal to zero.
Write the formula for the compound as the symbol for the metal and nonmetal, each followed by a subscript of the number determined in 2.
Writing Formulas from Names of Ionic Compounds
Early atomic theory and structure
Naming binary compounds
Binary ionic compounds contain only two different elements. The cation is written first in the formula, followed by the anion. When we write the name of the ionic compound, we add the suffix -
to the nonmetal.
Elements : Sodium (metal)
Name of the compound: Sodium chloride
Binary Ionic Compounds containing a Metal Forming Only One type of Cation
Binary Ionic Compounds Containing a Metal That Can form two or More Types of Cations
The metals in the center of the periodic table (including the transition metals) often form more than one type of cation. This can be confusing when you are naming compounds. The
is used to solve this problem. In the Stock System we designate the charge of the cation with Roman numeral placed in parentheses immediately following th name of the metal.
CuCl --> Copper (I) chloride
CuCl2 --> Copper (II) chloride
In classical nomenclature, when the metallic ion has only two cation types, the name of the metal is modified with the suffixes -ous and -ic to distinguish between the two. The lower-charge cation is given the -ous ending, and the higher one, the -ic ending.
Binary Compounds Containing Two Nonmetals
Compounds between nonmetals are molecular not ionic. Therefore, a different system for naming them is used. In a compound formed between two nonmetals, the element that occurs first in this series is written and named first:
Si, B, P, H, C, S, I, Br, N, Cl, O, F
The name of the second element retains the -ide ending as though it were an anion. A Latin or Greek prefix (mono-, di-, tri-, tetra- and so on) is attached to the name of each element to indicate the number of atoms of that element in the molecule.
RULES FOR NAMING BINARY COMPOUNDS CONTAINING TWO NONMETALS
Write the name for the first element using a prefix if there is more than one atom of this element.
Write the stem of the second element and add the suffix -ide. Use a prefix to indicate the number of atoms for the second element
Acids Derived from Binary Compounds
Certain binary hydrogen compounds, when dissolved in water, form solutions that have acid properties. Because of this property, this compounds are given acid names. For example HCl is a gas called hydrogen chloride, but its water solution is known as hydrochloric acid. To express the formula of a binary acid, it's customary to write the symbol of hydrogen first, followed by the symbol of the second element. To name a binary acid, place the prefix
in front, and the suffix
after, the stem of the nonmetal name. Then add the word
Naming Compounds Containing Polyatomic Ions
A polyatomic ion is an ion that contains two or more elements. Compounds containing polyatomic ions are composed of three or more elements and usually consist of one or more cations combined with negative polyatomic ion. Naming compounds containing polyatomic ions is similar to naming binary compounds. The cation is named first, followed by the name for the negative polyatomic ion.
Some elements form more than two different polyatomic ions containing oxygen. To name these ions, prefixes are used in addition to the suffix.
Hydrogen is the first element in the compounds formula.
The second part of the formula consists of a ployatomic ion containing oxygen.
Hydrogen is designated by adding the word acid so we don't write hydrogen in the formula. The name of the polyatomic ion is modified in the following manner:
-ate changes to an -ic ending
-ite changes to an -ous ending
The compound with the -ic ending contains more oxygen than the one with the -ous ending.
Chemists count atoms by weighing. Because we know average masses of atoms, we can count atoms by defining a unit to represent a larger number of atoms. Chemists have chosen the mole (mol) as the unit for counting atoms.
1 mol = 6.022 x 10^23 (Avogadro's number)
The atomic mass of an element in grams contains Avogadro's number of atoms and is defined as the molar mass of that element. To determine molar mass, we change the units of the atomic mass (found in the periodic table) from atomic mass units to grams.
1 molar mass = atomic mass of an element in grams
1 mol of atoms = 6.022 x 10^23 atoms
Molar mass of compounds
If the formula of a compound is known, its molar mass can be determined by adding the molar masses of all atoms in the formula.
The mass of 1 mol of a compound contains Avogadro's number of formula units.
For diatomic elements, we must take special care to distinguish between a mole of atoms and a mole of molecules. Ex: 1 mol of oxygen molecules, which has a mass of 32.00 g. This quantity is equal to 2 mol of oxygen atoms.
gives the smallest whole-number ratio of atoms present in a compound
is the true formula, representing the total number of atoms of each element present in one molecule of a compound.
The molecular formula can be calculated from the empirical formula if the molar mass is known.
n = molar mass/mass of empirical formula = number of empirical formula units
Chemical reactions always involve a change. The substances entering the reaction are called the
, and the substances formed are called the
In a chemical reaction atoms are neither created nor destroyed. All atoms present in the reactants must also be present in the products.
is a shorthand expression for a chemical change or reaction. It uses the chemical symbols and formulas of the reactants and products and other symbolic terms to represent a chemical reaction.
Reactants (left) are separated from the products (right) by an arrow (-->).
Coefficients are placed in front of substances to balance the equation and to know how many number of units we have.
Conditions required to carry out the reaction may, if desired, be placed above or below the arrow.
The physical state of a substance is indicated by the following symbols: (s) for solid state; (l) for liquid state; (g) for gaseous state; and (aq) for substances in aqueous solution.
The equation must be balanced. A
contains the same number of each kind of atom on each side of the equation.
Write the unbalanced equation as we learned previously.
Count and compare the number of atoms of each element on each side of the equation and determine those that must be balanced
Balance each element, one at a time, by placing whole numbers (coefficients) in front of the formulas containing the unbalanced element. Metals first, then nonmetals, then hydrogen and oxygen. A coefficient in front of a formula affects every atom in the formula.
Check all the elements after every coefficient is added.
Do a final check making sure that each element is balanced and that the smallest possible set of whole number coefficients has been used.
Combination Reaction (A + B --> AB)
Decomposition Reaction (AB --> A + B)
(A + BC --> B + AC )
(AB + CD --> AD + CB)
TYPES OF CHEMICAL REACTIONS
Molar mass = grams of a substance / number of moles of the substance
molar mass = grams of a monatomic element / number of moles of the element
number of moles = number of molecules / 6.022 x 10^23 (molecules / mole)
The area of chemistry that deals with quantitative relationships among reactants and products is known as stoichiometry. Solving problems in stoichiometry requires the use of males in the form of mole ratios.
A mole ratio is a ratio between the number of moles of any two species involved in a chemical reaction. EXAMPLE: 2 H2 + 02 --> 2 H2O six mole ratios can be written (2 mol H2 / 1 mol O2) or (2 mol H20 / 1 mol 02) and so on.
We use the mole ratio to convert the number of moles of one substance to the corresponding number of moles of another substance in a chemical reaction
Problem-Solving Strategy for Stoichiometry Problems
Determine the number of moles of starting substance
moles = (grams) (1 mole / molar mass)
Determine the mole ratio of the desired substance to the starting substance
mole ratio = moles of the desired substance in the equation / moles of starting substance in the equation
You multiply it by the moles of the starting substance.
Calculate the desired substance in the units specified in the problem
Limiting Reactant and Yield Calculations
In many chemical processes, the quantities of the reactants used are such that one reactant is in excess. The amount of the product(s) formed in such a case depends on the reactant that is not in excess. This reactant is called the
- it limits the amount of product that can be formed.
Scientists have studied energy and light for centuries, and several models have been proposed to explain how energy is transferred from place to place. One way energy travels through space is by electromagnetic radiation. Waves have three basics characteristics: wavelength (distance between consecutive peaks), frequency (tells how many waves pass a particular point per second), and speed (tells how fast a wave moves through space). A beam of light behave like a stream of tiny packets of energy called photons.
The Bohr Atom
Atoms can radiate light. Elements in the gaseous state give off colored light. When the light emitted by a gas is passed through a prism or diffraction grating, a set of brightly colored lines called a
Niel Bohr stated that electrons exist in specific regions at various distances from the nucleus. He also visualized the electrons as revolving in orbits around the nucleus.
Planck stated that energy is never emitted in a continuous stream but only in small, discrete packets called quanta. From this Bohr theorized that electrons have several possible energies corresponding to several possible orbits at different distances from the nucleus. Therefore an electron has to be in a specific energy level, it cannot exist in between.
Bohr was able to account for spectral lines of hydrogen this way. A number of energy levels are available, the lowest of which is called the ground state. When electrons falls from a high energy level to a lower one, a quantum of energy is emitted as light at a specific frequency, or wavelength. This light corresponds to one of the lines visible in the hydrogen spectrum. However Bohr's moethods of calculation did not succeed for heavier atoms. More theoretical work on atomic structure was needed.
Erwin Schrödinger, an Austrian physicist, created a mathematical model that described electrons as waves. Using Schroödinger's wave mechanics, we can determine the probability of finding an electron in a certain region around the nucleus of the atom.
It is important to recognize that we cannot locate an electron precisely within the atom; however it is clear that electrons are not revolving around the nucleus in orbits. The electrons are instead found in orbitals. An orbital is a region in space around the nucleus where there is a high probability of finding a given electron
Energy levels of Electrons
The electron is restricted to only certain allowed energies. The wave-mechanical model of the atom also predicts discrete principal energy levels within the atom. These energy levels are designated by the letter n, where n is a positive integer . The lowest principal energy level corresponds to n = 1, the next to n = 2 and so on. As n increases, the energy of the electron increases, and the electron is found on average farther from the nucleus. Each principal energy level is divided into sublevels. The first principal energy level has one sublevel. The second principal energy level has 2 sublevels, the third has 3 sublevels, and so on. Each of these sublevels contains spaces for electrons called orbitals.
An atomic orbital can hold a maximum of two electrons, which must have opposite spins.
s , p , d , f
Principal energy level-->
<-- number of electrons in sublevel orbital
--> type of orbital
Atomic Structures of the First 18 Elements
No more than two electrons can occupy one orbital
Electrons occupy the lowest energy orbitals available. They enter a higher energy orbital only when the lower orbitals are filled. For the atoms beyond hydrogen orbital energies vary as s < p < d < f for a given value n.
Each orbital in a sublevel is occupied by a single electron before a second electron enters. For example, all three p orbitals must contain one electron before a second electron enters a p orbital.
The electron configuration is a method that shows the arrangement of the electrons in an atom in their orbitals. In this method, we list each type of orbital, showing the number of electrons in it as an exponent. An electron configuration is read as follows.
We can also represent this configuration with an orbital diagram in which boxes represent the orbitals (containing small arrows indicating the electrons)
Valence electrons are the electrons in the outermost energy level of an atom.
Electron Structures and the Periodic Table
Each horizontal row in the periodic table is called a period. There are seven periods of elements. The number of each period corresponds to the outermost energy level that contains electrons for elements in that period.
Elements that behave in a similar manner are found in groups or families. These form vertical columns on the periodic table. The groups A are known as the
. The B groups and Group 8 are called the
The radii of the atoms tend to increase down each group and that they tend to decrease from left to right across a period. This is due to the number of energy levels that the elements have. The decrease from left to right is due to the fact that a proton is added to the nucleus and it makes the neutrons be more close to the nucleus.
The ionization energy of an atom is the energy required to remove an electron from the atom. Decreases down a group, increases across a row.
Lewis Structures of Atoms
The valence electrons, as we had already said, are the electrons placed in the outermost energy level of an atom. The valence electrons are responsible for the electron activity that occurs to form chemical bonds. The Lewis structure of an atom is a representation that shows the valence electrons for that atom. Lewis proposed to use the symbol of the elements and dots around the element representing the valence electrons.
The Covalent Bond: Sharing Electrons
A covalent bond consists of a pair of electrons shared between two atoms. This bonding concept was introduced by Lewis.
Covalent bonds are formed when two atoms share a pair of electrons between them:
This is the predominant type of bonding in compounds
True molecules exist in covalent compounds
Overlap of orbitals forms a covalent bond
Unequal sharing of electrons results in a polar covalent bond
There are many cases that the atoms are not different enough for a transfer of electrons but are different enough that the electron pair cannot be shared equally. This unequal sharing of electrons results in the formation of a
polar covalent bond
The attractive force that an atom of an element has for shared electrons in a molecule or polyatomic ion is known as its electronegativity. The polarity of a bond is determined by the difference in electronegativity values of the atoms forming the bond. If the electronegativities are the same, the bond is nonpolar covalent and the electrons are shared equally. A dipole is a molecule that is electrically asymmetrical, causing it to be oppositely charged at two points. A dipole is often written as +-
Lewis Structures of Compounds
Problem solving strategy
Obtain the total number of valence electrons to be used in the structure by adding the number of valence electrons in all the atoms in the molecule or ion. If you are writing the structure of an ion, add one electron for each negative charge or substract one electron for each positive charge on the ion
Write the skeletal arrangement o of the atoms and connect the with a single covalent bond.
Substract two electrons for each single bond you used in Step 2 from the total number of electrons calculated in Step 1. This gives you the number of electrons available for completing the structure.
Distribute pairs of electrons around each atom to give each atom a noble gas structure.
If there are not enough electrons to give these atoms eight electrons, change single bonds between atoms to double or triple bonds by shifting unbonded pairs of electrons as needed. Check to see that each atom has a noble gas electron structure. A double bond count as four electrons for each atom to which it is bonded.
Complex Lewis Structures
When a single unique Lewis structure cannot be drawn for a molecule, resonance structures (multiple Lewis sructures) are used to represent the molecule.
Compounds Containing Polyatomic Ions
Polyatomic ions behave like a single unit in many chemical reactions
The bonds within a polyatomic ion are covalent.
The Ionic Bond: Transfer of Electrons from One Atom to Another
The chemistry of many elements, especially the representative ones, is to attain an outer electron structure like that of the chemically stable noble gases. With the exception of the helium, this stable structure consists of eight electrons in the outermost energy level.
The ionic bonds are formed whenever one or more electrons are transferred from one atom to another
Ionic compounds do not exist as molecules: ions are attracted by multiple ions of the opposite charge to form a crystalline structure.
Metals tend to loose electrons and nonmetals tend to gain them.
Predicting formulas of Ionic Compounds
Chemical compounds are always electrically neutral: metals lose electrons and nonmetals gain electrons to form compounds. Stability is achieved (for representative elements) by attaining a noble gas electron configuration. In almost all stable chemical compounds of representative elements, each atom attains a noble gas electron configuration. This concept forms the basis for our understanding of chemical bond.
The Valence Shell Electron Pair Repulsion (VSEPR) Model
Draw the Lewis Structure for the molecule
Count the electron pairs around the central atom and arrange them to minimize repulsions (as far as possible). This determines the electron pair arrangement.
Determine the positions of the atoms
Name the molecular structure from the position of the atoms
Kinetic-molecular theory assumptions:
Gases are tiny particles with no attraction for each other.
The distance between particles is great compared to the size of the particles
Gas particles move in straight lines
No energy is lost in particle collision
The average kinetic energy for particles is the same for all gases at the same temperature and pressure.
A gas that follows KMT is an ideal gas
The kinetic energy of a particle is expressed as
KE = 1/2 mv^2
Gases will diffuse to mix spontaneously
Gases can effuse through a small opening
Graham's law of effusion states
rate of effusion for gas A sqrt.densityB
--------------------------------- = ------------------ =
rate of effusion for gas B sqrt.densityA
sqrt. molar mass B
sqrt. molar mass A
Pressure is force per unit area (P = F/A)
Pressure of atmosphere is measured by using a barometer:
Units of pressure include:
Atmosphere (atm) = 760 mg Hg
Pascal, 1 atm = 101325 Pa = 101,3 kPa
Torr. 1 atm = 760 torr.
Preassure is directly related to the number of molecues in tha sample and to the Kelvin of the sample
Measurement of Pressure of Gases
The Kinetic-Molecular Theory
At constant temperature, the volume of a gas is inversely proportional to the pressure of the gas
P1·V1 = P2 · V2
At constant pressure, the volume of a gas is directly proportional to the absolute temperature of the gas
V1 / T1 = V2 / T2
At constant volume, the pressure of a gas is directly proportional to the absolute temperature of the gas
P1 / T1 = P2 / T2
Combined Gas Laws
The P V T relationship for gases can be exressed in a single equation known as the combined gas law:
P1 3 V1 P2 · V2
---------- = ------------
One mole of any gas occupies 22.4 L at STP (1 atmosphere and 273.15 K )
The density of a gas is usually expressed in units of g/L
Temperature and pressure are given for a density of a gas since the volume depends on these conditions
Density of gases
Ideal Gas Law
The ideal gas law combines all the variables involving gases into a single expression:
PV = nRT
R is the ideal gas constant and can be expressed as:
R= 0.0821 L·atm/mol·K
FIRST CONVERT TO MOLES!
Real gases show derivation from the ideal gas law:
Derivations occur at:
These derivations occur because:
Molecules have finite volumes
Molecules have intermolecular attractions
Ozone in our upper atmosphere protects us from harmful ultraviolet radiation
The ozone layer is being destroyed by pollutants such as Freons and other chlorinated hydrocarbons:
These molecules produce free radicals, which interact with ozone to convert it to oxygen
In the lower atmosphere ozone causes damage to plants, cracking of rubber, and irritations to humans.
Other air pollutants such as nitrogen oxides and sulfur oxides are found in urban areas, creating smog, which can impact our daily lives.