NEETChemistryThermodynamics (C)
An ideal gas undergoes isothermal free expansion. Which of the following represents the correct combination of signs for the change in enthalpy ( H ), total entropy change ( S_ total ), and change in Gibbs free energy ( G )?
Options
- AH > 0 ; S_ total > 0 ; G < 0
- BH = 0 ; S_ total > 0 ; G < 0
- CH = 0 ; S_ total = 0 ; G = 0
- DH = 0 ; S_ total > 0 ; G > 0
Correct answer
B. H = 0 ; S_ total > 0 ; G < 0
Step-by-step solution
For the isothermal expansion of an ideal gas, the temperature remains constant ( T = 0 ). Since the enthalpy of an ideal gas depends only on temperature ( H = nC_p T ), the change in enthalpy H = 0 . Free expansion is a spontaneous, irreversible process. According to the second law of thermodynamics, the total entropy change of the universe for a spontaneous process must be positive ( S_ total > 0 ). The change in Gibbs free energy at constant temperature is given by the equation G = H - T S_ sys . During expansion