In which of the following equilibrium systems will an increase in the volume cause the equilibrium to shift away from the reactants and towards the products?

- H2 (g) + F2 (g) ⇌ 2HF (g)

- N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

- CaCO3 (g) ⇌ CaO (s) + CO2 (g)

- 2NOBr (g) ⇌ 2NO (g) + Br2 (g)

Answer: 2NOBr (g) ⇌ 2NO (g) + Br2 (g)

Explanation: For volume changes in equillibrium, the following are to be taken into consideration:

Volume changes have no effect on equillibrium system that contains solid or aqueous solutions. An increase in volume of an equilibrium system will shift to favor the direction that produces more moles of gas. A decrease in volume of an equilibrium system will shift to favor the direction that produces less moles of gas. Volume changes will have no effect on the equillibrium system if there is an equal number of moles on both sides of the reaction.

2NOBr (g) ⇌ 2NO (g) + Br2 (g) is the equillibrium system because there are more moles of products, therefore an increase in the volume of the reaction will shift to the right and produce more moles of products. Also both reactants and products exist in the gaseous state and does not have equal number of moles.