Thermodynamics C Question 3
Question 3 - 2024 (27 Jan Shift 1)
If three moles of an ideal gas at $300 \mathrm{~K}$ expand isotherrnally from $30 \mathrm{dm}^{3}$ to $45 \mathrm{dm}^{3}$ against a constant opposing pressure of $80 \mathrm{kPa}$, then the amount of heat transferred is _______ J.
Show Answer
Answer (1200)
Solution
Using, first law of thermodynamics,
$\Delta \mathrm{U}=\mathrm{Q}+\mathrm{W}$,
$\Delta \mathrm{U}=0$ : Process is isothermal
$\mathrm{Q}=-\mathrm{W}$
$\mathrm{W}=-\mathrm{P}_{\text {ext }} \Delta \mathrm{V}:$ Irreversible
$=-80 \times 10^{3}(45-30) \times 10^{-3}$
$=-1200 \mathrm{~J}$
