Question

We consider a thermodynamic system. If $\Delta U$ represents the increase in its internal energy and $W$ the work done by the system, which of the following statements is true ?

• A. $\Delta U = - W$ is an adiabatic process
• B. $\Delta U = W$ in an isothermal process
• C. $\Delta U = - W$ in an isothermal process
• D. $\Delta U = W$ in an adiabatic process

Answer 1

Answer: (A)

$\Delta U = - W$ is an adiabatic process

Answer 2

An isothermal process is a constant temperature process. In this process, $T=$ constant or $\Delta T=0$.
$\therefore \Delta U=n C_{V} \Delta T=0$
An adiabatic process is defined as one with no heat transfer into or out of a system. Therefore, $Q=0$. From the first law of thermodynamics.
$W =-\Delta U$
or $\Delta U = -W$