Question

According to the first law of thermodynamics, $\Delta U = q + w$. In special cases the statement can be expressed in different ways. Which of the following is not a correct expression?

• A. At constant temperature : $q - -w$
• B. When no work is done : $\Delta U = q$
• C. In gaseous system : $\Delta U = q + P\Delta V$
• D. When work is done by the system : $\Delta U = q + w$

Answer 1

Answer: (D)

When work is done by the system : $\Delta U = q + w$

Answer 2

When work is done by the system, $\Delta U=q-w$.