Question

A sample of gas is taken through cycle abca show

n

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 transf

erred as heat along path

bc?

Answer 1

(a) The change in internal energy along path ab can be found according to the second law of thermodynamics:

$$dQ_{ab}=dU_{ab}+W_{ab},\\dU_{ab}=dQ_{ab}-W_{ab}=5-4=1\text{ J}.$$

(b) The energy transferred as heat along path bc:

$$dQ_{ab}+dQ_{bc}+dQ_{ac}=2\text{ J},\\ 5+dQ_{bc}+3=2,\\ dQ_{bc}=-6\text{ J}.$$