Question

Each of the following reactions is allowed to come to equilibrium and then the volume is changed as indicated. Predict the effect (shift right, shift left, or no effect) of the indicated volume change. Drag the appropriate items to their respective bins.CO(g) + H2O(g) <=> CO2(g) + H2(g)
(volume is decreased)
PCl3(g) + Cl2(g) <=> PCl5(g)
(volume is increased)
CaCO3(s)<=> CaO(s) + CO2(g)
(volume is increased)

Answer 1

This is a question about LeChatelier’s rules. When it comes to volume changes, systems will shift equilibrium in ways that try to keep pressure stable. This usually means changing the total number of gas particles.

For the first reaction, there are two molecules of gas in both the reactants and the products. There is no benefit to favouring one side over the other because the total amount of gas will always be the same. Therefore decreasing the volume will have little or no effect on the equilibrium.

For the second reaction, there are two molecules of gas on the left and one on the right. If volume is increased, the equilibrium will shift in a way that produces more gas molecules in order to keep pressure equal. Therefore the equilibrium will shift left.

For the third reaction, there are no molecules of gas on the left and one on the right. By the same logic as the second reaction, the equilibrium will shift right.