Internal energy is

The internal energy change when a system goes from state $A$ to $B$ is $40 \, kJ/mol$. 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?

Calculate the work done when $2$ moles of an ideal gas expand from a volume of $5 \ dm^3$ to $7 \times 10^{-3} \ m^3$ against a constant external pressure of $2.02 \times 10^5 \ Nm^{-2}$. (in $kJ$)

Evaporation of water is

What is a system? Explain the types of systems.

An adiabatic process is .................