Question

For the following reaction, 2SO3(g) = 2SO2(g) + O2(g), the equilibrium constant, Kp, is 1.32 at 627 degrees Celsius. What is the equilibrium constant for the reaction: SO3(g) = SO2(g)+ 1/2 O2(g)

Answer 1

One thing that you should note quickly is that the equilibrium constant expression depends on how we write the chemical reaction.

For example, consider the following reaction

N2O5(g) < - > 2NO2(g) + 1/2O2(g) K = [NO2]2[O2]1/2/[N2O5]

However, we can just as easily multiply the whole reaction by 2- perhaps we don't like the stoichiometric coefficient of 1/2 in front of the oxygen. This gives

2N2O5(g) < - > 4NO2(g) + O2(g) K' = [NO2]4[O2]/[N2O5]2

K depends on how you write the chemical reaction! If you multiply the chemical equation by a given number (such as 2), it is the same as raising the equilibrium constant expression to that power. (K' = K2 in the above example.)

Answer 2

.870