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A diatomic gas undergoes a process represented on the P–V graph by a straight line that passes through the origin. The molar heat capacity for this process is

1. 4 R
2. 2.5 R
3. 3 R
4. 4R/3

Correct answer: 3 R

Solution

P proportional to V is PV^(-1) = const, so n = -1. C = Cv + R/(1-n) = 5R/2 + R/2 = 3R for a diatomic gas.

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