Answer to Question #100723 in Molecular Physics | Thermodynamics for Gordon Huy

Question

A sample of gas is taken through cycle abca shown in the p-V diagram of Figure 2. The net work done is +2.0 J. Along path ab, the magnitude of the work done is 4.0 J, the energy transferred to the gas as heat is +5.0 J. Along path ca, the energy transferred to the gas as heat is +3.0 J.
(a) What is the change in internal energy along path ab?
(b) How much energy is transferred as heat along path bc?

Answer 1

a)

$$U_{ab}=Q_{ab}-W_{ab}$$

$$U_{ab}=5-4=1.0\ J$$

b)

$$Q_{bc}=Q_{abca}-Q_{ab}-Q_{ca}$$

$$Q_{bc}=W_{abca}-(W_{ab}-U_{ab})-Q_{ca}$$

$$Q_{bc}=2-(4-1)-3=-4\ J$$