Question

Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas ? (Assume non-expansion work is zero)

• A. Cyclic process : $q = - w$
• B. Isothermal process : $q = - w$
• C. Adiabatic process : $\Delta U = - w$
• D. Isochoric process : $\Delta U = q$

Answer 1

Answer: (C)

Adiabatic process : $\Delta U = - w$

Answer 2

For cyclic process : $\Delta U = 0 \; \Rightarrow \; q = - w$ For isothermal process : $\Delta U = 0 \; \Rightarrow \; q = - w$ For adiabatic process : $q = 0 \; \Rightarrow \; \Delta U = W$ For isochoric process : $w = 0\; \Rightarrow \; \Delta U = q$

So, the correct option is (C): Adiabatic process : $\Delta U = - w$