21. Which one of the following phenomena occurs when gas in a piston-cylinder assembly expands reversibly at constant pressure?

A. Heat is added to the gas

B. Heat is removed from the gas

C. Gas undergoes adiabatic expansion

D. Gas does work from its own stored energy

Click for Answer/Explanation

Correct Answer is A

22. Change in enthalpy in a closed system is equal to the heat transferred if the reversible process takes place at constant

A. Internal energy

B. Entropy

C. Temperature

D. Pressure

Click for Answer/Explanation

Correct Answer is D

dQ = du + pdV

at constant pressure –

pdV = d(pV)

dQ (at const. Pr) = d(u + pV) = dh

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