Question

When/how do we know when(in what kind of problems), we have to apply Latent heat (L) in thermodynamics?

Answer 1

Latent heat is heat required to change phase of matter ,for example if we have water at 100 degree celcius then water will remain at that temperature until all water converted to vapor ,so if you provide heat to water which is at 100 degree celcius then you need to provide it Lv amount of heat to convert it's phase from water to vapor ,Lv is called latent heat of vaporization.

There in thermodynamics may occur different latent heat for different matters we need to apply to change its phase, at perticular temperature matter starts changing it's phase and it will remain at that temperature until all amount of matter changes it's phase and during this phase transition whatever amount of heat we transfer to it, is called "latent heat"