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A fixed amount of a monoatomic ideal gas at 1 bar pressure and 27 degrees C expands against vacuum (external pressure = 0) from a volume of 1.2 dm³ to 2.4 dm³. What is the change in Gibbs free energy (Delta G) of the gas? (Given: R = 0.80 bar-L per K per mol, ln 2 = 0.7)
- 0
- -64 bar.liter
- +84 J
- -84 J
Correct answer: -84 J
Solution
Free expansion keeps T constant (ideal gas, Delta_U=0). Delta_H=0, so Delta_G = -T*Delta_S = -T*n*R*ln(2). With n = PV/RT = 0.005 mol, Delta_G = -300 * 0.005 * 0.80 * 0.7 * 100 J = -84 J.
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