(1) The decomposition of N2O5 at 45°C is a first-order reaction, with a rate equation of Rate = k[N2O5]1. (2) Using the initial concentration and rate of decline provided, the rate constant k is calculated to be 5.733 x 10-4 s-1. (3) For the first-order reaction converting cyclobutane to 1-butene at 42°C, with a given rate constant and initial concentration, the concentration after 24 hours is calculated to be 3.9 x 10-3 M.

1. ANSWER ALL QUESTIONS
(a) The decomposition of N2O5 at 45C is a first-order reaction.
2N2O5(g)  4NO2(g) + O2(g)
i. Write the rate equation for the reaction.
ii. Calculate the rate constant if the initial concentration of N2O5 is
1.5x103
M and it declines at a rate of 8.6x107
M s1
.
(b) At 42C, the conversion of cyclobutane into 1-butene is a first-order
reaction and the rate constant is 1.20x105
s1
. If the initial
concentration of cyclobutane at the same temperature is 1.10x102
mol
L1
, what would be the concentration after 24 hours of reaction?
Chemistry Unit
Session 2013/2014
Semester 2
Sample QUIZ Paper
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2. Solution:
(a) (i) Rate = k[N2O5]1
(ii) Rate = k[N2O5]1
8.6 x 10-7
M s-1
= k [1.5 x 10-3
M]
k = 5.733 x 10-4
s-1
(b)
kt = ln
t
o
[A]
A][
(1.20 x10-5
s-1
) x (24x60x60) = ln
t
-2
[A]
10x1.1
t
-2
[A]
10x1.1
= e-1.0368
t
-2
[A]
10x1.1
= 2.82017799
[A]t = 3.9 x 10-3
M