Honors Chemistry

Answers to Chapter 12 Study Questions

 

1. a) 1 mole CO2

b) 0.050 - 0.030 moles/liter = 0.020 moles/liter

c) conc. of CO2 produced = conc. of CH4 used up

conc. of CO2 after 20 min = 0.050 - 0.020 = 0.030 mol/L

f) conc. of CO2 after 30 min = 0.050 - 0.015 = 0.035 mol/L

= -2(0.0010) = - 0.0020 mol/L/min

 

2 a) The mechanism, and therefore the number of steps in a reaction, are determined experimentally.

b) The second step; it's the slowest step.

c) rate = k x (concentration NO3) x (concentration NO)

d) rate increases by a factor of (1/2 x 3 = 3/2) 3/2

e) the order with respect to NO is 1; the overall order is 2.

 

activated complex

 
 


no catalyst

 
3.

200

+ catalyst

 
160

reactants

 
Energy 120

products

 
(kJ) 80

40

0

 

4. 1) concentration of reactants: Reaction rate increases as concentration of reactants increases because number of collisions increases, making reaction more likely to occur.

2) surface area of reactants: Rate increases as surface area of reactants increases because the greater the area of reactant exposed, the more likely are collisions that will result in product formation.

3) temperature: As temperature increases, rate increases because at higher temperature, a greater proportion of reactant molecules have a kinetic energy greater than the activation energy so a greater proportion of collisions result in product formation.

4) catalyst: Catalysts increase reaction rate by lowering the activation energy.

5) inhibitors: Inhibitors decrease reaction rate by destroying a catalyst, reducing effective surface area or by using up reactant.

 

5. a) 2 N2O(g) 2 N2(g) + O2(g)

b) N2O(g) N2 + O; N2O(g) + O N2 + O2

c) O

 

6. a) rate = k [HgCl2]n x [C2O42]m

2 = 2n ; n = 1

order with respect to HgCl2 is 1. (Rate is proportional to [HgCl2].)

4 = 2m ; m = 2

order with respect to C2O42- is 2. Overall order is 3.

b) rate = k [HgCl2] [C2O42-]2

c) rate = k [HgCl2] [C2O42-]2 ; 1.3 x 10-7 = k (0.10)(0.10)2; k = 1.3 x 10-7/0.001 = 1.3 x 10-4

d) rate = 1.3 x 10-4 x [HgCl2] [C2O42-]2; rate = 1.3 x 10-4 x (0.30) (0.30)2 = 3.5 x 10-6 mol/L/s