A change in pressure can affect only the volume of a gas, but not that of a
solid because solids (and liquids) are much less compressible. The stress applied is an
increase in pressure. According to Le Châtelier’s principle, the system will adjust to
partially offset this stress. In other words, the system will adjust to decrease the pressure.
This can be achieved by shifting to the side of the equation that has fewer moles of gas.
Recall that pressure is directly proportional to moles of gas: