CHM 51
Chapter 13 – Class activity part 3
Name
1. If the activation energy for a reaction is 100 kJ/mol (a typical value), what fraction of the molecules have
enough energy to get over the activation energy barrier at 300 K?
2. The reaction for the decomposition of dinitrogen monoxide gas to form oxygen radicals is:
N2O(g)  N2(g) + O(g). If the rate constant is 3.04 × 10-2 s-1 and the frequency factor is
8.00 × 1011 s-1, what is the activation energy for the first-order reaction at 700°C?
3. The gas-phase reaction of NO with F2 to form NOF and F has an activation energy of Ea = 6.30 kJ/mol
and a frequency factor of A = 6.00×108 M−1⋅s−1 . The reaction is believed to be bimolecular:
NO(g)+F2(g)→NOF(g)+F(g)
What is the rate constant at 595 ∘C ?
4. Rate constants for the decomposition of gaseous dinitrogen pentoxide are 3.7×10−5 s−1 at 25.0 ∘C and
1.7×10−3 s−1 at 55.0 ∘C.
2N2O5(g)→4NO2(g)+O2(g)
a. Determine the activation of energy in kJ/mol
Dang1
b. What is the rate constant at 35.0oC?
5. Consider the following mechanism for the reaction of hydrogen and iodine monochloride:
Step1.H2(g)+ICl(g)→HI(g)+HCl(g)
Step2.HI(g)+ICl(g)→I2(g)+HCl(g)
a. Write the overall reaction
b. Determine the intermediate(s) if any
c. What is the molecularity of each step
6. Consider the reaction: 2NO2(g) + F2(g)  2NO2F(g)
The experimental rate law is Rate = k[NO2][F2]
Show that the proposed mechanism for this reaction consists of the following elementary steps:
d. Step-1: NO2 + F2  NO2F + F; (slow, rate-determining)
e. Step-2: NO2 + F  NO2F;
(fast)
Dang2
7. The rate equation for the reaction:
Cl2(aq) + H2S(aq)  S(s) + 2HCl(aq) was found to be rate = k[Cl2][H2S]. Which of the following mechanisms
are consistent with this rate law?
(a) Cl2  2Cl- (slow)
Cl- + H2S  HCl + HS- (fast)
Cl- + HS-  HCl + S (fast)
Cl2 + H2S  S + 2HCl
(b) Cl2  2Cl- (fast)
Cl- + H2S HCl + HS- (fast)
Cl- + HSC  HCl + S (slow)
Cl2 + H2S  S + 2HCl
(c) Cl2 + H2S  Cl- + HS- + HCl (slow)
Cl- + HS-  HCl + S (fast)
Cl2 + H2S  S + 2HCl
Dang3