Chem 1000 : Work

Work involved in the expansion or compression of gases is called PRESSURE-VOLUME WORK. Work is expressed through the equation:

w= -P_ext x change in volume

 

When a gas expands, the change in volume is positive and the work is negative, signifying that then energy leaves the system as work. When a gas is compressed, change in volume is negative and work is positive, signifying that work enters the system. To summarize:

• Gas expand= Positive volume, negative work= energy leaves system as work
• Gas compresses = Negative volume, positive work = energy enters system as work

Note Pext is the external pressure, the pressure against which a system expands or the applied pressure that compresses a system. The SI unit for pressure is Joules. If pressure is stated as bars or atmospheres , convert as the following :

1 atm L = 101.325 J

1 bar L = 100 J