Three processes compose a thermodynamic cycle shown in the accompany P-V, diagram of an ideal gas :
Process 1\(\rightarrow\)2 takes place at constant temperature, during this process 60 J of heat enters the system
Process 2\(\rightarrow\)3 takes place at constant volume, during this process 40 J of heat leaves the system
Process 3\(\rightarrow\)1 is adiabatic
What is the change in internal energy of the system during process 3\(\rightarrow\)1 ?
Answer & explanation
Correct answer: option 4
1\(\rightarrow\)2 : isothermal; \(\Delta U_{12}\) = 0
2\(\rightarrow\)3 : isochoric; \(\Delta W\) = 0
\(\Rightarrow \Delta Q_{23} \Rightarrow -40 = \Delta U_{23}\)
For a cyclic process : \(\Delta U\) = 0
\(\Delta U_{12} + U_{23} + U_{31} = 0\)
0 + (-40) + \(\Delta U_{31}\) = 0
\(\Delta U_{31}\) = + 40 J