Arrhenius Questions with answers

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  • Created on: 03-03-13 12:57
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Arrhenius revision Questions
1. Calculate the rate constant using the Arrhenius equation given the following values
for a reaction : A = 2.22 x 1011 moldm-3s-1 ; Ea = 111 kJmol-1 ; T = 444 oC
2. The rate constant for the between Mg and HCl was measured at different temperatures. The
results obtained were:
T(K) 290 310 330 350
k (moldm-3s-1) 0.0030 0.0216 0.122 0.567
Use the Arrhenius equation to calculate the pre-exponential factor at 290K if the activation energy
was 55.5 kJmol-1
Q3. A series of experiments were carried out to investigate the effect of temperature on the rate
of reaction
(i) Complete the missing data in the table below.
Temperature (T) / K 1/ temperature (1/T) / K­1 Rate constant ln (rate constant)
295 3.39 × 10 ­3
2.88 × 10 ­3
­5.85
305 3.28 × 10­3 1.01 × 10­2 ­4.60
311 1.83 × 10­2
320 3.13 × 10­3 4.98 × 10­2 ­3.00
333 3.00 × 10­3 2.02 × 10­1 ­1.60
(ii) Plot a graph of ln (rate constant) on the vertical axis against 1/T on the horizontal axis
(iii) Use the Arrhenius equation together with your graph to calculate a value of the activation energy,
EA, for this reaction. Show all steps in your working. Include units in your final answer, which should be
given to two significant figures.
.....................................................................................................................
Answers
Q1 k = A exp(- Ea/RT) ; k = 2.22 x 1011 x exp(- 111,000/8.31 x 717)
k = = 2.22 x 1011 x 8.11486193.. x 10-9 = 180 moldm-3s-1 (to 3 sig fig)
Q2 k = A exp(- Ea/RT) ; 0.0030 = A x exp(- 55,500/8.31 x 290)
0.0030 = A x 9.95858...... x 10-11 A = 3.01 x 107 moldm-3s-1 (to 3 sig fig
Q3 (i) 3.22 × 10­3 ; -4.00 correct sig fig needed for 1 mark eg -4 = no mark
(ii) labelled axis, sensible scale = 1 ;
correct plotting and good line of best fit (no double / broken/ thick lines ) =1
(iii) Gradient = - 10823 K; [ allow range -11200 to -10400 ] (unit not needed for mark )
Ea = 10823 x 8.31 = (+) 889939 J mol-1 (1)
= 90 kJmol-1 or 90,000 J mol-1 to 2 sig fig (1) (no unit = no mark)

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