Question

Given reaction is
$3X\left(g\right)+Y\left(g\right)\rightleftharpoons 3Z\left(g\right)$
$\Delta H=+35kJ$
Which conditions will give the highest yield of $Z$ at equilibrium?

• A. High temperature and high pressure.
• B. High temperature and low pressure.
• C. Low temperature and high pressure.
• D. Low temperature and low pressure.

Answer 1

The correct option is A High temperature and high pressure.

Pressure conditions:
Calculating $\Delta n_g$
$\Delta n_g=3-4=-1$
$\Delta n_g<0$
The reaction takes place with reduction in number of gaseous moles in the forward side.For the yield of product to be the highest i.e. $Z\uparrow$ , a high pressure should be applied so that the reaction favours the side where there is a reduction in number of gaseous moles i.e. the product side. So a high pressure is favourable for $Z\uparrow$

Temperature conditions:
We can see that the reaction is endothermic because $\Delta H>0$. The reaction occurs with an decrease in temperature from reactants to the product side. When a high temperature is chosen, reaction tends to favour the direction in which there is a decrease in the temperature. Hence, for the product Z yield to be the highest, a high temperature should be chosen so that the reaction favours the product side.
Note: Effect of T is explained using van't Hoff equation.