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When 1 mol of an ideal gas is heated at constant volume, its temperature rises from 298 K to 308 K and 500 J of heat is supplied. Which of the following statements is correct?

1. q = w = 500 J, delta_U = 0
2. q = delta_U = 500 J, w = 0
3. q = w != 500 J, delta_U = 0
4. delta_U = 0, q = w = -500 J

Correct answer: q = delta_U = 500 J, w = 0

Solution

At constant volume, w = P*delta_V = 0. By the first law of thermodynamics, delta_U = q - w = 500 - 0 = 500 J.

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