The industrial manufacture of ethanol from ethene is a catalysed reversible reaction. The equation for this reaction is:
C2H4(g) + H2O(g)֖ C2H5OH(g) ΔH = – 46 kJ mol –1
Which of the following changes in conditions, when made independently, would increase the number of moles of ethanol present at equilibrium?
1 increasing the overall pressure
2 increasing the temperature
3 the addition of more catalyst.

Answer:

6) B

Increasing the overall pressure results in the position of equilibrium moving in the direction of the fewest moles of gas. In the reaction, there are 2 moles of gases on the left (reactants) and 1 mole of the gases on the right (products). Therefore, increasing the overall pressure would favour the forward reaction in which ethanol is produced and its number of moles would increase. So 1 is correct.
The reaction in the equation is exothermic as the AH is a negative value.
As a rule, an exothermic reaction favours the reverse reaction (more reactants are formed than products). Number of moles of ethanol would decrease so 2 is wrong.
Addition of more catalyst would not affect the position of equilibrium. So, it would neither increase nor decrease moles of ethanol. So 3 is wrong.