# ChemIIA 2012 final.pdf Page 1...4 5 67817

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Chemistry IIA, IIA(Ecochem), IIA(Mol Drug Des), IIA(Nanosci Mat) June 2012

QUESTION 4
The natural logarithm of the rate constant (ln k) is plotted against the reciprocal of the absolute temperature for
the decomposition of N2O. The best-fit linear curve has an equation shown below in the plot.
4

ln k

2
0
0.0008

0.001

0.0012

-2

y = -30317x + 29.346
-4
-6
-8
-1

1/T (K )

What is the value of the activation energy of this reaction?
[Total for question 4 = 3 marks]

QUESTION 5
(a)

Briefly explain why the following rate law for the chemical reaction below is unlikely.
2NO2(g) + F2(g)  2NO2F(g)
Rate = k[NO2]2[F2], where k is the rate constant
[1 mark]

(b)

In fact, the experimentally determined rate law for the reaction is Rate = k[NO2][F2]. Propose a simple
and acceptable mechanism that satisfies the rate law.
[2 marks]
[Total for question 5 = 3 marks]

QUESTION 6
The decomposition of hydrogen iodide,
2HI(g)  H2(g) + I2(g)
has rate constants of 9.51 x 10-9 L/mols at 500 K and 1.10 x 10-5 L/mols at 600 K. Calculate the activation
energy. Hint: the frequency factor A is independent of temperature.
[Total for question 6 = 4 marks]
[Total for Part B = 30 marks]
- - - END of PART B - - -

Course ID. 104311, 104312, 104313, 104314

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