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A piston filled with 0.04 mol of an ideal gas expands reversibly from 50.0 mL to 375 mL at a constant temperature of 37.0°C. As it does so, it absorbs 208 J of heat. The values of q and w for the process will be: (R = 8.314 J/mol K) [ln 7.5 = 2.01]

1. q = +208 J, w = −208 J
2. q = −208 J, w = −208 J
3. q = −208 J, w = +208 J
4. q = +208 J, w = +208 J

Correct answer: q = +208 J, w = −208 J

Solution

Heat absorbed q = +208 J. For an isothermal process of an ideal gas dU = 0, so w = -q = -208 J. Thus q = +208 J, w = -208 J.

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