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Chemistry 12

A summary of the chemistry 12 course !

heather macfarlane

on 25 January 2013

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Transcript of Chemistry 12

Chemistry 12 1.1 Measuring the Rate in a Chemical Reaction 1.2 Methods of Measuring Reaction Rates 1.3 Factors that affect Reaction Rates Reaction rates are given in a expression of the change in concentration over time.
The equation for calculating the rate of a chemical reaction is...
change in amount
change in time To figure out the rate of a reaction, there are 5 different physical properties we could measure. The rate of a reaction depends on two things. It depends on the nature of the reactants and the conditions the reaction occurs under. Fast Reactions: Fireworks are an example of a fast reaction rate. different elements are different colours. By using a spectrophotometer you can determine the intensity of the colour and the reaction rate. Rate= change in colour intensity --------------------
change in time Temperature Change If a reaction produces heat, the temperature changes can be graphed and measured.
Rate=temperature change
Change in Time Mass Change If there is only one solid present,
you can measure the rate by
measuring its change in mass.
Rate= change in mass
change in time. Colour Change Concentration Change If a reaction uses up all of an acid, you can measure the [H+] with a PH meter.
Rate= change in [H+(aq)]
change in time Pressure Change Slow Reactions: Metal rusting is an example of something with
a slow reaction rate. you can only use pressure change to measure
the change in gases, just measure the change
in pressure. Rate= change in pressure
change in time temperature when you increase the temperature of a reaction you increase the average kinetic energy of the particles. Concentration of the Reactants There are two different reaction types that are increased by an increase in concentration of the reactants. these are homogeneous and heterogeneous. Homogeneous Reactions
These are reactions between two of the same phases. These reactions tend to be faster because they are able to fully mix and collide. Heterogeneous Reactions This is a reaction between two different phases. For example: liquid and a gas or a solid and a gas. A heterogeneous reaction can also happen between two solids...how is this possible... This is possible because solids can be in different forms They could be powder. They could be in chunks Another important fact is that surface area can effect the reaction rate! However the surface area only applies to HETEROGENEOUS reactions. Reaction rates Aqueous>>Gas>>Liquids>>Solids Fastest slowest Pressure pressure can also help determine a reaction rate. However it only applies to gases. Nature Of The Reactants Some reactions are naturally slow while others can be naturally fast. The slow reactions are slow because their bonds are strong and unreactive. The fast reactions break weak bonds there fore they are fast. example: Erosion of a statue VS. a wild fire spreading Slow Fast Ability Of Reactants to Meet surface area The more surface area = higher ability of reactants to collide = greater reaction rate! Phase Consideratioins the different phases of reactants can effect the reaction rate. (Gas,solid,liquid) Catalyst and Inhibitors A chemical which when added to a reaction will speed up the rate of the reaction without being used.

An inhibitor will reduce the rate of a reaction. Catalyst Inhibitor example: An inhibitor slows down the reaction rate. As a metaphore, it is like the breaks on a bike. The breaks slow down the speed of a bike just like an inhibitor would slow down a reaction rate Question
A) Nature of reactants
B) presence of a catalyst
C) temperature of reactants
D) surface area of reactants which of the following only affects the rate of a HETEROGENEOUS reaction? Answer D) Surface area of reactants 1.5 Reaction Rate and Collision Theory In collision theory it is believed that molecules and atoms are round spheres that bounce off one another. For a chemical change to occur 2 things must happen... Sufficent energy In order for atoms to rearrange they must collide with sufficient energy . Geometry They atoms must also collide with correct geometry in order to pair and split properly Question How does decreasing the temperature influence reaction rate? Answer the particles would slow down therefore they may not have the speed they need to collide correctly(sufficient energy) 1.6 Enthalpy changes in Chemical Reactions When chemical reactions happen, chemical bonds are broken and new molecules are formed. the potential energy is now different. Two things could happen. Energy is absorbed to form products = Endothermic Energy is released to form products = Exothermic Endothermic means products have more energy then reactants. "Absorbs heat" Endothermic Exothermic products have less energy than reactants Exothermic losing heat "giving it away" Co2 C + O2 H = + 393kj This reaction is ENDOTHERMIC because the heat term is + on the right **you can think of + as "gaining" heat** Heather Macfarlane Unit two Reaction Equlibrium 2.1 dynamic equilibrium A reversible reaction is a reaction when reactants can form products and products can go back and form reactants A<----->B + heat Equilibrium When the rate of the forward and reverse reactions are equal, the reaction is at equilibrium **In order for equilibrium to happen the system must be closed** Dynamic Equilibrium microcopic changes occur (ones you cant see) but macroscopic changes do not(ones you can see) 2.2 characteristics of equilibrium 1. system is closed
2. forward and reverse reactions have the same rate
3. temperature remains the same levels of randomness 1. solids are not very random
2. pure liquids are much more random than solids.
3.solutions are more random than pure liquids
4. gases are more random than solutions gases>> solutions>> pure liquids>> solids entropy and enthalpy are in opposite directions = equilibrium happens
entropy and enthalpy favour the products = 100% completion
entropy and enthalpy favour the reactants= 0% completion Unit One 2.3 Predicting weather or not a reaction is spontaneous Spontaneous reaction A change that will happen all own its own. It does not need assistance. Enthalpy = heat Example Ariel the chihuahua LOVES enthalpy. She sits close to the fire so that she can absorb the heat from the fire to warm her tiny body. Entropy = randomness Example Stella the chihuahua prefers entropy over enthalpy. She likes to surround herself with a chaotic mess of blankets and dog beds. She likes to keep her spot a mess. ** a good way to tell enthalpy (heat) and entropy (randomness) apart, is to remember that entropy has an "R" in it and it means randomness** Question:
the entropy of a system is a term used to describe:
A) randomness
B) heat content
C) average kinetic energy
D) stored chemical energy Answer A) entropy is randomness In the following reaction will entropy increase or decrease? 2H2(g) + O2(g) goes to 2H2O(g) Answer The entropy will decrease because as the reaction proceeds, it is getting less random. the reactants have 3 gases while the products only have 2 2.4 Le Chatelier's Principle Le Chatelier's Principle states that: If a closed system at equilibrium is subjected to change, processes will occur that will tend to counteract that change My own words Nature will try to undo whatever it is that we try to do. We cant stop the change, it will just naturally counteract what we do Things that change the equilibrium are called stresses. These are things like temperature or pressure. But of course pressure only affects gases. 1. effect of temperature change if we decrease heat the reaction will shift to produce more heat. Example: if heat is on the reactant side, the reaction will shift to the reactant side to produce more heat. 85kj + A +B goes back and forth to AB Heat decreases the reaction will shift to make up for heat loss 2. effect of concentration if a certain element in a reaction is decreased, the reaction shifts to make up for that loss. A+B goes back and forth to AB +56kj A is decreased reaction shifts 3. effect of pressure **Only effects gasses** a decrease in volume increases pressure, which increases the concentration. 2AB(g) + C(g) goes back and forth to 2ABC(g) + 58kj there are 3 gases on reactant side there are only 2 gases on produce side Example if we increase pressure on reactant side then the reaction will shift to make up for the loss. Question which of the following will cause the NH3 at equilibrium to increase? A) an increase in O2
B) a decrease in volume
C) a decrease in temperature
D) an increase in temperature 4NH3(g) + 3O2(G) goes back and fourth to 2N2(g) + 6H2O(l) heat = -1530kj Answer = D)
this is because the heat would want to shift towards the reactant side and NH3 is on the reactant side, therefor you would get more NH3 2.6 equilibrium expression and equilibrium constant Keq= products
reactants Example A(g)+B(g) goes to AB(g)
Keq= [AB]
[A] [B] ** if an equation only has one solid or one gas you leave them out of the Keq.** A(S) +B(L) goes to AB(g)
Keq =AB helpful info: only temperature can effect Keq value. if Keq is large Keq favors products
if Keq is small Keq favors reactants Reaction equilibrium calculations there are 3 possible things you could be asked to calculate 1. Keq
2. consentrations of products, reactants, or both
3. initial concentrations. 2NO2(g) + O2(g) goes back and forth to 2NO2(g) question A 2.0L container contains 6.00 mol of NO2(g), 3.0 mol of NO(g) and .20 mol of O2(g) at equilibrium. what is the keq for There are 3 steps we would take to solve this question. step one write Keq expression Step 2: substitute equilibrium concentrations
Step 3: solve 1. Keq =[NO2]2
[NO]2 [ O2] **DONT FORGET EXPONENTS** [no2] = 6mol
-------- = 3
2L [NO] = 3 mol
--------- = 1.5
2L [o2]= .2mol
-------- = 0.1
2L step 2 Step 3 (3)2
------------ = 40
(1.5)2 (0.1) math behind equation 3.3 = 9
divide by 0.1=
then divide by (1.5)2 = 40 now you can solve a keq equation!! Unit 3 Solubility 3.1 solubility Electrolyte substances that dissolve. Their solution is able to conduct electricity and it contains ions more ions = more electrical conductivity Non- Electrolyte Substances that dissolve but do not conduct electricity and contains molecules metal + non metal = ionic
polyatomic = ionic
non metal + non metal = molecular Solubility the concentration of an equilibrium of a substance in solution at a certain temperature A saturated solution a solution that can no longer dissolve anymore. some is dissolved in solution and some has began to form a solid at the bottom of the solution 1. some undissolved materials must be involved
2. There must be an equilibrium between the dissolved and undissolved materials Question which condition is essential to prepare a saturated solution of an ionic salt? A) an excess of solute
B)any amount of solute
C) a temp. of 25 degrees
D)a fixed volume of solvent answer = A) an excess of solute excess of solute 3.2 Calculating Solubility Dilution calculations : when we mix a solution with another we are diluting them. calculation = diluted substance x old volume
diluted volume 3.3 predicting solubility soluble VS. non soluble low soluble: if a substance in a saturated solution has a concentration of less than .1 M then it has a low solubility will a precipitate form? a precipitate is the solid stuff that does not dissolve at the bottom of a solution. we can predict weather or not a precipitate will form. If a precipitate is able to form, there are three different reaction equations we can represent it by. 1. formula equation
2. total ionic equation
3. net ionic equation formula equation reactants and products are in a balanced chemical equation example: total ionic equation shows only the SOLUBLE ionic species broken up into their ions example Net Ionic Equation only shows the species that are involved in forming a precipitate. example Question which net ionic equation best describes the reaction that exists in a solution prepared by mixing equal volumes of 0.20M Ca(NO3)2 and 0.20M Na2CO3 A) Ca +2(aq) +CO3-2(aq) back and forth to CaCo3 (s)
B) Ca(NO3)2(aq) + Na2CO3(aq) back and forth to 2NaNO3(s) +CaCo3(s)
C) Na+(aq) +NO3-(aq) goes back and forth toNaNO3(S) Answer = A because B isn't a net ionic equation and it is not C because NO3- mixed with anything is soluble and a precipitate will NOT form precipitate Na2SO4(aq) + 2CaS(aq) 2NaS(aq) + Ca2SO4(S) 2Na+1(aq) + SO4-2(aq) + 2Ca+1(aq) + S-1(aq) 2Na+1(aq) + S-1(aq) + Ca2SO4 (s) 2Ca+1(aq) + SO4-2(aq) ca2SO4(s) Ksp = Solubility Product constant AB(s) back and forth to A+1(aq) +B-1(aq) example Ksp = [A+][B-] **you wouldn't include AB(s) becasue it is a SOLID** Trial Ksp 1. write out dissociation
2. write out Ksp 3 possible outcomes
1. Q<Ksp = precipitate can not form
2. Q=ksp = saturated solution is formed (no noticible precipitate)
3. Q>Ksp = a precipitate will form Question The solubility of Mg(OH)2 is found to be 1.2 x 10-4M What is it's Ksp? Mg(OH)2 Mg+2 + 2OH- 1.2 x 10-4 1.2 x 10-4 2.2 x 10-4 this # is doubled because
of the coefficient! this # is the molarity Ksp = [Mg+2][OH-]2 Ksp = (1.2 x 10-4)(2.4 x 10-4)2 **don't forget to square it** how to solve using a calculator... 2.4 x 10-4 multiplied by 2.4 x 10-4 =
answer x 1.2 x 10-4 =
answer = 6.9 x 10-12 trial Ksp question When solutions of AgNO3 and NaCl are combinded, the trial Ksp for AgCl is 5.6 x 10-11. predict what will be observed. A) a precipitate will form becasue trial Ksp < Ksp
B) a precipitate will form because trial Ksp > Ksp
C) a precipitate will not form becasuse trial Ksp < Ksp
D) a precipitate will not form because trial Ksp > Ksp Answer C) a precipitate will not form because trial Ksp < ksp how do we know this ... ksp = 1.8 x 10-10
trial Ksp = 5.6 x 10-11 this is a bigger # which means Ksp > trial Ksp = a precipitate will NOT form Chapter 4 Acids and Bases What is an acid? An acid is something that will release H+ in water what is a base? A base is something that will release OH- in water Arrhenius deffinitions Acids also start with "H" HCL, H2SO4 Bases end with "OH" NaOH or NH3 Question A substance that produces Hydrogen ions in solution is a definition of what? A) an Arrhenius acid
B) an Arrhenius base ANSWER = B acids = conduct electricity, turn litmus paper taste sour red bases = conduct electricity, turn litmus paper taste bitter blue Bronsted - Lowery theory acid = DONATES a proton
Base = ACCEPTS a proton Amphoteric = a substance that can either be an acid or a base. Question what is a general characteristic of a
Bronsted- Lowery base? A) they accept H+
B) they accept OH- answer= A Bronsted - Lowery bases accept H+ Conjugate acid - base pair : a pair of chemicals that only differ by one proton example HCO3 + HSO4 goes back and forth H2CO3 + SO4 ** HSO4 donated a proton to HCO3** Strong VS weak acids and bases strong = 100% ionized in solution example: AB(S) back and forth to A+(AQ) + b-(AQ) weak = less than 100% ionized in solution example: HF(AQ) + H2O back and forth to H3O(aq) + F(aq) your ears popping when you change in elevation in an airplane is an example of pressure change example of mass change example of colour change Ka = acid ionization constant when a WEAK acid reacts with H2O CH3COOH(aq) + H2O(L) back and forth to CH3COO(aq) + H3O Ka= [CH3OO][H3O]
-------------------- = 1.8 X 10-5
[CH3COOH] Kb= base ionization constant NH3(aq) + H2O(l) back and forth to NH4(aq) +OH(aq) when a WEAK base reacts with H2O Kb = [NH4][OH]
---------------- = 1.79 x 10-5
[ NH3 ] PH AND POH PH = ACIDIC = 0 - 6
= NUTRAL = 7
= BASIC = 8-14 POH = ACIDIC = 8 - 14
= BASIC = 0 - 6 = -log10[H3O] = -log10[OH] [H3O] [pH] [OH] [pOH] Kw = [H3O][OH] pH + pOH = 14 pOH = -log[OH] antilog(-pOH) pH = -log[H3O] antilog(-pH) Converting between pH, pOH, [H3O], [OH] Question if pH = 9.355, what is pOH? how to solve pH + pOH = 14
9.355 + pOH = 14
14 - 9.355 = 4.645
ANSWER = 4.645 question #2 if [ H3O] = 5.28 X 10-5M what is pH? how to solve pH = -log [ 5.25 X 10-5]
PH = 4.28 fact: acids and bases also can effect the environment Hydrolysis Is a reaction between a salt and a water to be an acidic or basic solution! there will be some ions that will not react with
the water, they are called spectator ions NaOH Na + OH since this is 100% ionized, the Na is a spectator ion! Li, Na, K, Rb, and Cs are all and will not react CIO4, I, Br, Cl, and NO3 all will not react because they are spectator anions spectator cations Question is NaCl acidic, basic, or neutral? how to solve step one. dissociate NaCl Na + Cl step two. cross out spectator ions NaCl Na + Cl NaCl = basic! Ice box questions a completly solved ice table will include the following information 1.original concentration of the weak acid
2. Ka for the acid
3. [H3O] or pH of the acid solution lets review the ice table! AB goes back and forth to A+ + B- I [initial] 0 0
C -change +change +change
E Question
If Ka = 1.8x10-5 for CH3COOH, what is the pH of a 0.50M solution of CH3COOH? How to solve... step one: CH3COOH H+ + CH3COO- Write out equation step two I .50 0 0 fill in intitial step three: C -X +X +X fill in change (use x because we don't know the #) step four E ------------------------------------------ .50-X X X Fill in what your end results could potentialy be step five Ka = [H][CH3COO]
[CH3COOH] = 1.8 x 10-5 = X2
[.50-X] Write in your Ka equations step six **this is where the tricky algebra comes in** .50 X 1.8 x 10-5 = X2
------ X .50
.50 *assume.50 - X = .50** assume .50 - x - .50 so the "X" is gone. then multiply .50 by both sides to get rid of the denominator step seven 9 x 10-6 = X2 = 3 x 10-3M 9 X 10-6 comes from multiplying .50 by 1.8X10-5. you then square both sides and get 3 X 10-3M which = "x" therefore we must fill in the ice table. pH then = -log [H] which = 2.50 Unit Five Electrochemistry Electrochemistry is converting chemical energy into electrical energy positive for a redox reaction, the reaction is expected to be spontaneous.
If E0
cell is negative for a redox reaction, the reaction is non-spontaneous.this is an example of
an electrochemical cell! There are two types of reactions we look at in electrochemisty 1. Oxidation reaction = a half reaction which electrons
2. Reduction reaction = a half reaction which electrons gains loses these two reactions go hand in hand. where there is an oxidization reaction there must be a reduction reaction Pb+2 + 2e- Pb(s)
CO(S) Co+2 + 2e- this reaction is a reaction reduction this reaction is a reaction oxidizing ** this is beacuse the Pb became more negative which meant it gained electrons as the reaction proceeded **this is because the Co became more positive which means it lost electrons as the reaction proceeded there is also what is called and oxidizing agent and a reduction agent.
oxidizing agent = reduced during reaction
reduction agent = oxidized during reaction **the oxidizing reaction will have the reducing agent and the reduction reaction will have the oxidizing agent** Question time!! in the following equations which one is the reduction reaction and which is the ozidation reaction. Also label the reducing and oxidizing agents. Cl2 + 2e- 2Cl-
Ag(s) Ag+ +2e- Reduction reaction which also will be the oxidizing agent Oxidization reaction which also will be the reducing agent gains electrons loses electrons 5.2 Oxidation Numbers oxidization numbers are going to be explained through and example KMnO4 what are the oxidation numbers 1. for this the overall charge is 0 there for all of the oxidization numbers together must equal 0
2. separate the example into its own parts K Mn O 3. now we start with what we know. we know that oxygen has a charge of -2 and since we have four of them we multiply the charge of -2 by how many we have which is 4 which gives us -8 K Mn 4O-2 -8 4. now we move on to the next this we know. we know that K has a charge of +1 and since there is only one of them its number is +1 K Mn 4O-2 -8 +1 5. so far our total = -7. we have to get that number to equal 0 which is our overall charge. so what plus -7 will give us 0. it must be +7. this means that Mn = +7 K Mn 4O-2 -8 +7 +1 =0 these are your oxidation numbers!! spontanious vs non spontanious in order for a reaction to be spontanious the one element must be higher on the left and the other lower on the right!
the two that are circled in blue will spontanioustly react! Balancing half reactions there are four steps to solving a half reaction 1. balance MAJOR atoms first
2. balance OXYGEN atoms by the addition of H2O
3. balance HYDROGEN atoms by the addition of H+
4. balance the OVERALL charge by adding electrons Balance the following reaction CNO- CN- This reaction by following the steps becomes... 1e- + 2H+ +CNO- CN- +H2O The electrochemical cell Anode = cathode = electrode where oxidation occurs electrode where reduction occurs electrons flow anode to cathode!! **lets pretend that the Cu is actually Pb Question the reaction at the anode is
A) Pb Pb+2 +2e-
B) Pb+2 + 2e- pb
C)Zn+2 +2e Zn
D) Zn Zn+2 + 2e- Answer = D
This is becasue the anode is the Zn because out of the two half reaction it is the oxidation reaction which means that it is losing electrons! this is the last section of my chemistry 12 project !!!!! voltage if the E cel is positive you can expect a spontanious reaction
if the E cell is negative you can expect a non spontanious reaction! the only thing you really need to know for voltage in this unit is that you would take the voltage of the anode from the data booklet and subtract it from the cathode! Question 3Cu+2 + 2Cr 2Cr+3 + Cu the E for the cell is .. A) 0.40V
D)2.50V ANSWER=C you now know all there is to know about chemistry 12!!
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