1. Chemistry 12 Unit 1- Reaction Kinetics
1.1 – Introduction
1.2 – Methods of Measuring Reaction Rates
1.3 – Factors affecting Reaction Rates
1.4 – Experimental Measurement of Reaction Rates
1.5 – Reaction Rates and Collision Theory
1.6 – Enthalpy Changes in Chemical Reactions
1.7 – Kinetic Energy Distributions
1.8 – Activation Energies
1.9 – Reaction Mechanisms
1.10 – Energy Diagram of a Reaction Mechanism
1.11 – The Effect of Catalysts on the Activation Energy
1.12 – The Effect of a Catalyst on the Reaction Mechanism
1.13 – Some Uses of Catalysts

2. Unit 1.1 – Introduction (p. 1-2)
What is Reaction Kinetics?
Reaction Kinetics - The study of the rates of reactions (rx) and the factors which affect the rates
*(note: “rx” = reaction(s))

4. Expressing Rates rate = quantity of a product formed unit time or
rate = quantity of a reactant consumed
unit time
in general: rate = ∆ amount (a reactant or product)
∆ time
*(Note: A time unit is always in the denominator of a rate equation.)

5. Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq)
Example:
Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq)
r = ∆ mass of Zn r = ∆ [ HCl ]
∆ time ∆ time
r = ∆ volume H2
∆ time
*(note: [ ] = molar concentration)

6. Textbook Examples (p.2):
a) If 16 g of HCl are used up after 12 min in a certain reaction, then the average reaction rate is: b) If a reaction between CaCO3 and HCl produces 245 mL of CO2(g) in 17s, the average reaction rate is:
a. Rate of using HCl = 16g/12min = 1.3g/min
b. Rate of producing CO2 = 245 mL/17s = 14 mL/s
Do ex. 1-5 p.2 S.W. (SW is Hebden’s Student Workbook)

7. Mg(s) + 2H+(aq) + 2Cl-(aq) H2(g) + Mg2+(aq) + 2Cl-(aq)
Note - some rxs, when written in ionic form show that some ions don’t change concentration.
eg. Mg(s) + 2HCl(aq)  H2(g) + MgCl2 (aq)
Note: To write an equation in IONIC FORM, dissociate all the aqueous (aq) compounds:
ionic form : (use ion chart to help)
Mg(s) + 2H+(aq) + 2Cl-(aq) H2(g) + Mg2+(aq) + 2Cl-(aq)
*[Cl-] does not change as rx proceeds (spectator ion)

8. Write 4 possible equations which express rate:

9. Calculations Involving Reaction Rates
When doing calculations involving rate, amount (grams, moles, Litres etc.) use the general equation:
Rate = ∆ amount (g, mol, L)
∆ time (s, min)
∆ amount = Rate x ∆ time
∆ time = ∆ amount
Rate

10. Tips: When doing calculations: Keep in mind: Always include units
Make sure your units cancel out properly
Always use conversion factors
Keep in mind:
Significant figures
Stoichiometry

11. Example: Solve for ? : 0.020 mol = ? mol min s
*The 60 in 60 s/1min is an exact number by definition. Therefore, we don’t consider it using significant digits. The has 2 sig figs, therefore the answer has 2.
0.020 mol x 1 min = 3.3 x 104 mol
1 min s s

12. You also must use molar mass to go grams   moles
Ex: 0.26 mol Zn = ? g of Zn min s
0.26 mol Zn x g Zn x 1min = g of Zn
1 min mol Zn s s

13. You would use 22.4 L for conversions moles L (STP) for gases
Ex: mol O2 = ______ L (STP)
s s
*0.030 has 2 sig digs so the answer must have 2 sig figs
**Note: This conversion is ONLY used for GASES at STP!
0.030 mol O2 x 22.4 L = 0.67 L O2
1s mol s

14. Try this problem:
The rate of a reaction is g of Mg per second. Calculate the number of moles of Mg used up in 6.0 minutes.

15. Comparing Rates using Balanced Equations
Use coefficient ratios - only proportional to mol /s (not to g/s) Ex: 2C2H6 + 7O2  4CO2 + 6H2O consumed produced Ex: If ethane is consumed at a rate of mol /s, calculate the rate of consumption of O2 in mol /s
0.066 mol C2H6 x 7 mol O2 = mol O2
s molC2H6 s

16. Ex: 2C2H6 + 7O2  4CO2 + 6H2O If ethane is consumed at a rate of 0
Ex: 2C2H6 + 7O2  4CO2 + 6H2O If ethane is consumed at a rate of mol /s calculate rate of production of CO2
0.066 mol C2H6 x 4 mol CO2 = mol CO2
s 2 molC2H6 s

17. Mole Bridge
When other units are used, you must use moles

18. Ex: Al + 3Br2  2AlBr3
Calculate the rate of consumption of Br2 in g/s if 67.5 g of Al are consumed per second
*You may have to use a few conversions and the “rate equation” to arrive at an answer. As you did in Chem. 11, make a “plan” first and make sure your units all cancel the correct way!
(you may go from L  L of one gas to another at STP)
(67.5g Al/s) x (1molAl/27.0g Al) x (3molBr2/2 mol Al) x (159.8g Br2/1 mol Al) = 599g Br2 /s

19. 2Al(s) + 6 HCl (aq)  3 H2 (g) + 2 AlCl3 (aq)
Example: An experiment is done to determine the rate of the following reaction:
2Al(s) + 6 HCl (aq)  3 H2 (g) + 2 AlCl3 (aq)
It is found that the rate of production of H2 (g) is g/s.

20. Calculate the mass of Aluminum reacted in 3.0 minutes.

21. Unit 1.2 – Methods of Measuring Reaction Rates (p.2-5)
There are different methods for measuring different reactions. - Must look at subscripts & use common sense.
Ex: CaCO3(s) + 2HCl(aq)  H2O(l) + CO2(g) + CaCl2 (aq)

22. CaCO3(aq) + 2H+(aq)  H2O(l) + CO2(g) + Ca2+(aq)
Ionic form:
CaCO3(aq)+2H+(aq)+ 2Cl-(aq)H2O(l)+CO2(g)+ Ca2+(aq)+2Cl-(aq)
Net ionic form:
CaCO3(aq) + 2H+(aq)  H2O(l) + CO2(g) + Ca2+(aq)
*In an open system CO2(g) escapes
As CO2 escapes, mass of the rest of the system will decrease

23. This rate could be expressed as..
r = ∆ mass of container and contents
∆ time (open system)

24. Note: For a changing rate (slope), which is more realistic, rate could be expressed over a certain time interval
Do Q#6 p. 3

25. Monitoring Reaction Rates
Properties which can be monitored (measured at specific time intervals) in order to determine rx rate
Note: Must consider  Subscripts (s)(l)(g)(aq)
 Coefficients of gases
 Heat (endo or exo?)

26. Methods of Measuring Reaction Rates: a) Colour Change

28. b) Temperature Change
- In exothermic reactions, temperature of surroundings will increase - In endothermic reactions, temperature of surroundings will decrease - Measured in insulated container (calorimeter)

29. c) Pressure Change
*Constant volume or sealed container*
If more moles of gas (coefficient) in products, pressure will go up
0 mol of gas  1 mol of gas
If more moles of gas (coefficient) in reactants, pressure will go down
H2(g) + ZnCl2(aq)  Zn(s) + 2HCl (aq)
1 mol of gas  0 mol of gas

30. If equal mol of gas, pressure will not change
2 mol of gas  2 mol of gas

31. d) Volume Change *Constant pressure Ex: balloon *
If more gas is produced, volume of a balloon will increase

32. e) Mass Change
If only one solid is used up, could remove periodically and weigh it:
If one gas is produced and escapes, measure mass of what’s left in container (mass of container and contents)

33. Note: it’s not practical to measure masses of (aq) substances separately since they are mostly water.

34. f) Changes in Molar Concentration of Specific Ions
Eg:
The concentration of a specific ion can be measured using spectrophotometer or periodic samples taken and titrated to measure concentration

35. g) Acidity Change

36. If H+ is a reactant (or any acid HCl, HNO3 etc
If H+ is a reactant (or any acid HCl, HNO3 etc.) [H+] will decrease so pH will INCREASE! (less acidic) rate = ∆ pH ∆ time *Measured using a pH meter

37. Homework:
Read p. 1-5
Do Questions:
1.1 - p.2 #1-5
1.2 – p. 3-5 #6-9