A gas at STP has a volume of 1.0 liter. If the pressure is doubled and the temperature remains constant, the new volume of the gas will be ... ?

PV = nRT

A gas at STP ... This means that the temperature is 0°C and pressure is 1 atm.

R is the gas constant which is 0.08206 L*atm / (K*mol)

Rearranging for volume

V = nRT/P

The temperature and number of moles are held constant. This means that this uses Boyle's Law. (The ideal gas law could be manipulated to give us this result when T and n are held constant.)

PV = k

where k is a constant.

This means that

P₁V₁ = k = P₂V₂

P₁V₁ = P₂V₂

(1 atm) * (1 L) = (2 atm) * V₂

V₂ = 0.5 L

The new volume of the gas is 0.5 L.