For questions about gas pressure, or the effect of pressure in general on chemical species, substances, or reactions.

A measure of the force per unit area exerted by a volume of a substance, most commonly a gas or a liquid; the SI unit is the Pascal (Pa), which equals 1 Newton per square meter [$$\pu{1Pa}$ = \pu{1N/m^2} = \pu{1kg/(m*s^2)}$].