Question

Which thermodynamic parameter is not a state function?

• A. q at constant pressure
• B. q at constant volume
• C. W at adiabatic
• D. W at isothermal

Answer 1

The correct option is D W at isothermal

(d)
H ad U are state functions but W and q are not state functions.
From the equation, $\Delta H=\Delta U+\Delta PV$

At contant pressure,$\Delta H=\Delta U+P\Delta V$

$\Delta P=0,\Delta H=q_p$

so, it is a state function.

At constant volume,$\Delta H=\Delta U+V\Delta P$

$\Delta V=0,\Delta U=q_v$
so, it is a state function.

Work done in any adiabatic process is state function.
$\Delta U=q-W$ ($\therefore$ q = 0)
$\Delta U=-W$

Work done in isothermal process is not a state function.

$W=-q(\because \Delta T=0,q\ne 0)$
Hence, option (d) is correct.