Single correct option
One mole of a diatomic ideal gas (rotational but no vibrational modes active) undergoes a process in which its pressure is directly proportional to its volume, . During the process its volume doubles. The fraction of the heat absorbed that is converted into work done by the gas is
- A.
- B.
- C.
- D.
Show answer and solution
Answer: (C)
With and we get , so doubling the volume quadruples the temperature: , where . The work done is . The internal energy change for a diatomic gas is . By the first law, . Therefore . Equivalently the molar heat capacity along this path is , giving . As a check, write . Since , , so , and the molar heat capacity of the path is , which again gives . Thus exactly one sixth of the heat supplied appears as work, and the other five sixths raise the internal energy of the gas.
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