Question

The standard enthalpy change for the reaction is 2so2+o2--> <-- 2so3 is -198 kj. The reaction efficiency can be increased by :

a. increasing pressure and using high temperature

b.increasing pressure and using moderate temperature

c.decreasing pressure and using high temperature

d.decreasing pressure only

e. decreasing pressure and using low temperature

The answer is B, however, please explain why that is true. How would the answer change if it was endothermic?

Thank you for your help!

Answer 1

According Le Chatelier's principle

With increasing pressure equilibrium shifts towards the side with fewer number of moles of gases. There are three moles on reactant side and two moles on products side. So increasing pressure favors the formation of more amount of products SO3.

The reaction is exothermic, so high temperature shifts equilibrium to the left side. So low temperature favors the formation of products. But decreasing temperature causes to decrease the rate of reaction. So moderate temperature is favorable to increase efficiency of reaction.

Hence option B) increasing pressure and using moderate temperature increases the efficiency of the reaction.