Question

If three moles of an ideal gas at 300 K expand isothermally from 30 dm3 to 45 dm3 against a constant opposing pressure of 80 kPa, then the amount of heat transferred is ______ J.

Answer 1

Using the first law of thermodynamics:

$\Delta U = Q + W$

For an isothermal process, $\Delta U = 0$, so $Q = -W$.

$W = -P_{\text{ext}} \Delta V = -80 \times 10^3 \times (45 - 30) \times 10^{-3} = -1200 \, \text{J}$