An ideal gas occupies an unknown volume V liters (L) at a pressure of 12 atm . The gas is expanded isothermally against a constant external pressure of 2 atm so that its final volume become 3 L . The work involved for this expansion process is ____ cal(Round off to two decimal places) (Gas constant $\mathrm{R}=0.082 \mathrm{L} \mathrm{atm} \mathrm{mol}^{-1} \mathrm{K}^{-1}=2 \mathrm{cal} \mathrm{mol}^{-1} \mathrm{K}^{-1}$ )
Answer
SELF-PRACTICE — the source book printed no answer.
Nothing is invented here, so this question has no answer on record.
Explanation
Answer: −121.95 cal — V = 2 × 3/12 = 0.5 L. w = −P_ext ΔV = −2 × 2.5 = −5 L atm = −5 × (2/0.082) cal = −121.95 cal.