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During isothermal compression of an ideal gas, which of the following statements is correct?

1. Work done on the gas (w) is positive
2. Enthalpy change (delta H) is zero
3. Heat released by the gas (q_gas) is negative
4. Enthalpy change (delta H) is positive

Correct answer: Enthalpy change (delta H) is zero

Solution

For an ideal gas, internal energy and enthalpy depend only on temperature. In an isothermal compression, T is constant, so delta U = 0 and delta H = 0. Work done on the gas is positive. The gas releases heat (q_gas < 0). Among the listed options, delta H = 0 is the unambiguous correct statement.

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