Work of Gas Expansion

A gas confined, such as the gas in this cylinder, exerts a pressure on the surfaces that confine it. Pressure is a measure of the force exerted on a unit area. The pressure confining the gas in the cylinder is measured by the force on the piston per unit area. When a gas expands it does work against the surroundings. In this case the gas does work by lifting the piston. The work done is given by the force exerted times the distance over which the force operates. In the expansion of the gas the force is exerted over the distance, shows as delta h (Δh). The work done is given by the product of the volume change times the pressure: Work = F × Δh = P × A × Δh = PΔV The pressure might be kept constant in such an expansion by heating the gas continuously as it expands. If the pressure is not constant, the formula is still correct, but pressure must be evaluated at each stage of the expansion.