Explaining pressure increase in terms of concentration

[Samantha Chung 4I]

Since we should avoid using the comparison of number of moles of gas to explain our logic, for instance in HW problem (7th edition 5J 5). How do we explain whether the following will lead to more products or reactants?

2O3g) -> 3O2(g)

[804994652]

increasing pressure favors the side with fewer moles of gas, in this case it would be reactants

[AngelaZ 1J]

If pressure is increased by decreasing volume, then concentration increases (C=n/V). We can calculate Q using the new concentrations and compare that with K to see which way the reaction shifts. In this case, we can look at [O2]^3/[O3]^2 to know that increasing concentration would cause Q>K and the reaction would shift left.