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Laws of Thermodynamics
GATE 2009
Medium
An ideal gas at temperature T1 and pressure P1 is compressed isothermally to pressure P2(>P1) in a closed system. Which ONE of the following is TRUE for internal energy (U) and Gibbs free energy (G) of the gas at the two states?
- AU1=U2, G1>G2
- U1=U2, G1<G2
- CU1>U2, G1=G2
- DU1<U2, G1=G2
Explanation
For an ideal gas, U depends only on T, so isothermal compression gives U1=U2. At constant T, dG=VdP>0 as pressure increases, so G increases with compression: G2>G1, i.e. G1<G2.
Source: GATE CH 2009 (2009)
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