CHBE 3300
Recitation 4
Office Hours 4 Worksheet
Problem 1.
The irreversible reaction A+B+H2O→C is performed in an aqueous solution. The following
initial rate data were measured at 20oC.
CAo
CBo
Initial rate
[mol L-1] [mol L-1] [mol L-1 s-1]
0.2
1.0
2
0.05
1.0
0.5
0.05
0.5
0.25
0.05
1.0
0.5
(a) It is known that the reaction order in water is 1. Since the reaction occurs in dilute
aqueous solution, water is in excess (Cwater = 55.5 mol L-1) and the system is
constant volume. What is the reaction order in A and B? What is the value of the
rate constant (including units)?
(b) If initial concentration of CAo = 1 mol/L and CB0 = 2 mol/L, what is the time required
to achieve 99% conversion of A?
(c) An enzyme was added to lower the activation energy from 10 kJ/mol to 5 kJ/mol.
At the same time, the reaction temperature was increased from 20 oC to 60 oC.
For this new condition, what is the time required to achieve 99% of A?
CHBE 3300
Recitation 4
Problem 2.
Given below is the concentration data for a first order irreversible elementary reaction
(A → B) in a batch reactor.
t
CA
[s] [mol L-1]
0
?
10
100
20
60
30
30
40
12
50
5
60
2
What is the rate constant (k) and initial concentration of A (CAO)?
Problem 3.
(From Hill 4.4) The thermal decomposition of bis(trifluoromethyl)trioxide proceeds through
the following overall reaction which obeys first-order kinetics.
The following mechanism has been proposed. Demonstrate whether the mechanism is
consistent with the rate expression observed experimentally.
CHBE 3300
Recitation 4
Problem 4.
(From Hill 4.8) The oxidation of ammonia in the presence of ClO occurs by the following
mechanism:
𝑘1
𝑁𝐻3 + 𝐶𝑙𝑂 → 𝑁𝐻2 + 𝐻𝑂𝐶𝑙
𝑘2
𝑁𝐻2 + 𝑂2 → 𝑁𝑂 + 𝐻2 𝑂
𝑘3
𝑁𝐻2 + 𝑂2 → 𝐻𝑁𝑂 + 𝑂𝐻
𝑘4
2𝐻𝑁𝑂 → 𝐻2 𝑂 + 𝑁2 𝑂
Experimentally, it is observed that H2O and N2O are produced in a 1:1 ratio. What does
this observation, in conjunction with the mechanism above, tell you about the ratio of rate
constants k3 and k2?