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

Correct Answer: 1200

Using the first law of thermodynamics:

\[ \Delta U = Q + W \]

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

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