Can latent heat exist when both phases cannot exist at same temperature?

Question

This is my understanding (please tell me if i am going wrong anywhere):

During phase change (i.e. ice melting into water) the molecules absorb heat, gain more random kinetic energy, and spread apart (leading to weaker intermolecular bonds). When all the molecules are separated enough to become fluid, they turn into water. However, in a real life scenario some molecules become fluid earlier than the others. In this case, any heat added to the 'ice' goes into separating the bonds and the temperature stops rising. Latent heat is the energy required to sufficiently separate all the bonds enough to change phase.

My question is: If water and ice could not co-exist at the same temperature (0 degrees Celsius), would there still be a latent heat and the 'plateau regions' on a heating curve. If any of my reasoning is wrong, please explain why the temperature stops rising during phase change.

If two phases cannot exist at the same temperature than you don't have an equilibrium first order phase transition between them. — Jon Custer, Mar 18 '24 at 14:42
Have you studied phase diagrams yet? What do you propose the phase diagram would look like for a material where solid and liquid phases can't exist at the same temperature? (And not because of sublimation) — The Photon, Mar 18 '24 at 15:29
First-order melting is not the gradual spreading and weakening of bonds as you describe. Please see Why, exactly, does temperature remain constant during a change in state of matter? — Chemomechanics, Mar 18 '24 at 15:52

Bob D · Answer 1 · 2024-03-18T17:32:52.407

During phase change (i.e. ice melting into water) the molecules absorb heat, gain more random kinetic energy, and spread apart (leading to weaker intermolecular bonds).

During phase change there is no increase in temperature and so no increase in random kinetic energy. There is only an increase intermolecular potential energy causing breakage of bonds.

When all the molecules are separated enough to become fluid, they turn into water.

Ice is converted to water at constant temperature all during the phase transition. This requires 334 kJ of heat for each kg of ice melted (latent heat of fusion). When all the ice becomes water the change in phase is complete. Additional heating raises the temperature of the water until the next phase change begins.

My question is: If water and ice could not co-exist at the same temperature (0 degrees Celsius), would there still be a latent heat and the 'plateau regions' on a heating curve

But water and ice do in fact co-exist during phase transition. Liquid and gas also co-exist during the phase transition from liquid to gas. For the liquid to gas transition, at 1 atmosphere 2260 kJ of heat is required to convert each kg of water to water vapor (latent heat of vaporization).

Hope this helps.

Can latent heat exist when both phases cannot exist at same temperature?

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