Phase Equilibrium at Constant Pressure
Most recent answer: 06/12/2016
- Shreya Singh (age 17)
Varanasi, Uttar Pradesh, India
I'm baffled that you were told the answer is (B). The flexible container means, I presume, that the pressure remains at 1 atmosphere, so that T=0°C is the melting/freezing temperature. If some of the ice melts, that would soak up latent heat, causing T to drop, causing freezing. If some more ice would form, that would release latent heat, raising T and causing ice to melt. In other words, the equilibrium between water and ice is stable. For a given amount of enthalpy (thermal isolation), the starting ratio remains the lowest free-energy condition.
Mike W.
p.s. On thinking more about it, here's how someone may have gotten confused. The external pressure would do a little positive work on the water as it melts because water has less volume than ice. You might think that would heat the material up and drive more melting. However, this small effect is already included in the latent heat.
(published on 06/12/2016)