Final answer:
The magnitude of work required to expand a gas against a pressure P is given by the formula W = PΔV.
Step-by-step explanation:
The formula that gives the magnitude of work required to expand a gas against a pressure P is given by:
W = PΔV
This means that the work done by the gas is equal to the product of the pressure and the change in volume of the gas.
For example, if the gas expands by a certain volume against a constant pressure, the work done by the gas can be calculated using this formula.