ANSWER ALL QUESTIONS

(a)

The decomposition of N2O5 at 45C 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

1.5x103 M and it declines at a rate of 8.6x107 M s1.

(b) At 42C, the conversion of cyclobutane into 1-butene is a first-order

reaction and the rate constant is 1.20x105 s1. If the initial

concentration of cyclobutane at the same temperature is 1.10x102 mol

L1, what would be the concentration after 24 hours of reaction?

Chemistry Unit

Session 2013/2014

Semester 2

Sample QUIZ Paper

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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 = lnt

o

[A]

A][

(1.20 x10-5 s-1) x (24x60x60) = ln t

-2

[A]

10 x 1.1

t

-2

[A]

10 x 1.1 = e-1.0368

t

-2

[A]

10 x 1.1 = 2.82017799

[A]t = 3.9 x 10-3 M