Question

The internal energy change when a system goes from state $A$ to $B$ is $40kJmol{e}^{-1}$. If the system goes from $A$ to $B$ by a reversible path and returns to state $A$ by an irreversible path, what would be the net change in internal energy?

• A. $40kJ$
• B. $Zero$
• C. > $40kJ$
• D. < $40kJ$

Answer 1

Answer: (B)

Internal energy $=△U=n{C}_v△T$ (It is a state function i.e independent of it’s path)

Let the state $A$ be $(P_1,V_1,T_1)$ and B be $(P_2,V_2,T_2)$

When the system goes from $A$ to $B$ (reversibly) and $B$ to $A$ (irreversibly). So, final state comes to be $A(P_1,V_1,T_1)$.

$△U_{A\to B\to A}=n{C}_v△T=n{C}_v(T_2-T_1)=0$