Which of the following would be an irreversible process?
a) Adiabatically compressing an ideal gas with an external pressure that equals the internal pressure
b) Allowing an ideal gas in a piston to expand isothermally against a constant pressure
c) Boiling an aqueous salt solution at a temperature where its vapor pressure equals the external pressure
d) Adding heat to a glass of ice water at 0°C so that some of the ice melts