Fig The net work done by the system in the process aba is –500 J.

Fig A p-V diagram (Example 17-4)

KINDS OF THERMODYNAMIC PROCESSES ADIABATIC – NO HEAT TRANSFER; Q = 0;  U = -W ISOCHORIC – CONSTANT VOLUME;  U = Q ISOBARIC – CONSTANT PRESSURE; W = p (V 2 – V 1 ) ISOTHERMAL – CONSTANT TEMPERATURE; only for ideal gas  U = 0, Q = W The First Law of Thermodynamics Q =  U + W or  U = Q - W

Fig Processes for an ideal gas: adiabatic Q=0 isochoric W=0 isothermal  U=0

Fig The internal energy of an ideal gas depends only on its temperature, not on its pressure of volume.

Fig Raising the temperature of an ideal gas by various processes Q =  U + W and  U = f(T) Isochoric W=0 so Q=  U Isobaric Q =  U + p(V 2 -V 1 )