Name _____________________

Lecture 2: Chemical Kinetics and the Rate Law

1. Does an increase in the concentration of reactants increase or decrease the rate of reaction? Explain why

2. In the reaction H2(g) + I2(g) 2HI(g) we discover rate=k [ H 2 ] [I 2]a. What is k called?

b. What is the overall reaction order for this reaction?

c. What is the order of reaction with respect to H2?

d. What is the order of reaction with respect to I2?

Assuming that the rate law is of the form

rate=k [ClO2 ]x ¿¿

a. Determine x

b. Determine y

3

a. Determine k from experiment 1

b. Determine k from experiment 2

c. Determine k from experiment 3

d. Determine the instantaneous rate when [ClO2] = 0.100M and [OH-] = 0.050M (hint use the rate law)

4. The rate of the reaction:

                                   BrO3-  (aq) + 5Br-  (aq) + 6H+  (aq) ) ⟶ 3Br2  (aq) + 3H2O 

was studied using the method of initial rates and the following information was obtained:

[BrO3-]0

(M)[Br-]0(M)

[H+]0(M)

Initial RateM/s

0.10 0.10 0.10 8.0x10-4

0.20 0.20 0.10 3.2x10-3

0.20 0.10 0.10 1.6x10-3

0.10 0.10 0.20 3.2x10-3

The general rate law for this reaction will be ….

rate=k ¿¿

a. Determine x

b. Determine y

c. Determine z

d. Determine the average value of the rate constant k (and include the units)

e. Write out the complete rate law inserting the appropriate value for k (including units), x, y, and z

Rate =

3. Consider the isomerization reaction CH3CN CH3NC conducted at 230oC. When [CH3CN] is plotted vs time we obtain a gentle decaying curve. When ln[CH3CN] is plotted vs time is plotted we get a straight line with a slope of -6.3x10-4 s-1. a. Is the reaction zero order? Explain why/why not

b. What is the order of the reaction with respect to CH3CN? Explain why

c. What is value of the rate constant for the reaction (don’t forget units)?

d. Write out the rate law including the value for k for this reaction

e. If we started with 1.0M of CH3CN how long would it take for it to decay to 0.5M?

f. What is the instantaneous rate for the reaction at t=3s?

4. In the hydrolysis reaction C4H9Cl + H2O(l) è C4H9OH + 2 HCl, the general rate law is

ratet=k ∙ [C4H 9Cl ]tx ∙ [ H2O ]t

y

the H2O concentration is so high that it is effectively constant [ H 2O ]t❑ [ H 2O ]o

❑ (around

55M). We can define a new rate constant k’=(k ∙ [H 2O ]oy )

ratet k ∙ [C4H 9Cl ]tx ∙ [ H 2O ]o

y=(k ∙ [ H 2O ]o

y ) ∙ [C4 H 9Cl ]tx=k ' ∙ [C4H 9Cl ]t

x

orratet k ' ∙ [C4 H 9Cl ]t

x

Now the rate law only involves the C4H9Cl so we can use the integrated rate law method to find x. Since over time only the [C4H9Cl] significantly changes

When the [C4H9Cl] is plotted versus time it is found to be a gentle curve. a. Is the reaction zeroth order?

b. To test if the reaction is first order we plot LN[C4H9Cl] vs time, this too is a gentle curve. Is the reaction first order?

c. Finally you plot 1/[C4H9Cl] vs time and you get a straight line graph with a slope of -2.01E-3 M-1s-1. Write the rate law in the form rate = k [C4H9Cl]x, giving x = , k = . (don’t forget the units)

Rate =