Consider the following gas-phase reaction: 2A(g)+B(g)⇌C(g)+D(g) A mixture of reactants and products at equilibrium is subjected to a series of changes. Determine which changes affect the composition of the equilibrium mixture, but leave the value of the equilibrium constant Kc unchanged, affect the value of the equilibrium constant Kc, or affect neither the composition of the equilibrium mixture nor the value of the equilibrium constant Kc.