We limit our discussion to calculation of the amout of work involved when a system expands or contracts against a constant pressure.

Calculating the Amount of Expansion Work at Constant Pressure Associated With a Volume Change

1. Determine V, the change in volume in cubic meters, m³, using the equation:
   

   Note: It may be necessary to convert the volumes to cubic meters.

2. Determine P, the restraining pressure in Pascals.

3. Calculate the work involved using the equation:
   

   Note: If the pressure has units of Pascals and the volume units of m³, the work will have units of Joules. Work done by a system (as the system expands) has a negative value. Work done on a system (as the system shrinks) has a positive value.