Fehling S Test / Benedict S Test s1

C. Y. Yeung (AL Chemistry)

F 7 Revision Exercise (Chemical Equilibria)

Name: ______Class: ______( ) Date: ______

1. The industrial preparation of methanol can be represented by the following equation: catalyst

CO(g) + 2H2(g) CH3OH(g)

The graph below shows the mole percentage of methanol in the reaction mixture against time at the same pressure but at two different temperatures:

mole % of methanol in the reaction mixture

100 2000C E D

0 50 400 C B C

0 A time 0 (a) With reference to the graph, answer the following questions: (1) What difference between the two initial rates of reaction can be deduced? Explain your deduction.

(2) Why do both curves eventually become horizontal?

(3) Explain whether the reaction for the production of methanol is exothermic or endothermic.

(b) At a given temperature and pressure, how would an increase in the amount of CO in the system affect the yield of methanol? Explain your answer.

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(c) On the above graph, sketch and label two curves which would be obtained if the process were carried out under the same conditions as those for the curve ABC, except that: (1) no catalyst is used (label this curve as I). (2) a higher pressure is used (label this curve as II).

2. The energy profiles of the reaction

A(g) + B(g) C(g)

under two different catalysts X and Y are represented below. y y g g r r e e n n e e

l l a a i i t t n n e e system with catalyst X system with catalyst Y t t o o p p

A, B A, B

C C (a) What is the effect of increasing temperature on the equilibrium of each system?

(b) What is the effect of decreasing pressure on the equilibrium of each system?

(c) Compare the effect of increasing temperature on the rate of reaction in the two system.

(d) Why could the use of a different catalyst change the order of the reaction?

3. The manufacture of sulphuric acid by the Contact Process in the presence of finely

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divided vanadium (V) oxide can be represented by the following equation:

-1 2SO2(g) + O2(g) 2SO3(g) H = -197 kJ mol

(a) State the effect of an increase in pressure on the system in equilibrium. Briefly explain your answer.

(b) Explain why the conversion of sulphur dioxide to sulphur trioxide is carried out industrially at a temperature of about 4500C, rather than at lower temperatures.

(c) What is the purpose of using vanadium (V) oxide, and why should it be finely divided?

4. The reaction between ethanoic acid and ethanol can be represented by the following equation:

CH3COOH(l) + CH3CH2OH(l) CH3COOCH2CH3(l) + H2O(l)

12.01g of ethanoic acid are treated with 4.61g of ethanol in the presence of a catalyst. When the reaction reaches equilibrium at 298K, 5.04g of ethanoic acid are found to have reacted. (a) Calculate the equilibrium constant for the reaction at 298K.

(b) What additional mass of ethanol would be required in order to use up a further 0.60g of ethanoic acid?

(c) Would the addition of more of the same catalyst affect the value of Kc? Explain.