If the reaction (NH4)3CO3 <--> 2NH3 + CO2 + H2O were at equilibrium, increasing the volume of the container would cause the concentration of the reactants and products to decrease. This would shift the equilibrium to the left, in favor of the reactants. This is because the equilibrium constant is directly proportional to the concentrations of the products, so decreasing the concentration of the products would require the reaction to shift to the left in order to restore equilibrium.