Question

Which of the following equilibria would not be affected by pressure changes at constant temperature?

Answer 1

Answer:

Option A) CO(g) + 1/2O2(g) <=> CO2(g).

Explanation:

A background knowledge of reaction rates shows that pressure will only affect gaseous reactant.

Further more, we understood that for pressure to effectively affect gaseous molecules, the total volume of the gaseous reactant must be different from the total volume of the gaseous products.

Now, let us consider the equation given in the question:

A) CO(g) + 1/2O2(g) <=> CO2(g).

B) CaCO3(s) <=> CaO(s) + CO2(g).

C) 2H2(g) + O2(g) <=> 2H2O(l).

D) 2Hg(l) + O2(g) <=> 2HgO(s).

E) CO2(g) + H2(g) <=> CO(g) + H2O(g).

From the above, only option A and E has gaseous reactant and product.

For option A:

CO(g) + 1/2O2(g) <=> CO2(g).

Total volume of reactant = 1 + 1/2 = 3/2 L

Total volume of product = 1 L

Since the volume of the reactant and that of the product are different, therefore, a change in pressure will affect the reaction.

For option E:

CO2(g) + H2(g) <=> CO(g) + H2O(g).

Total volume of reactant = 1 + 1 = 2 L

Total volume of product = 1 + 1 = 2 L

Since the volume of the reactant and that of the product are the same, therefore, a change in pressure will have no effect in the reaction.