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Phase changes occur at fixed temperatures for a given substance at a given pressure, and these temperatures are called boiling and freezing (or melting) points. During phase changes, heat absorbed or released is given by \ (Q = mL,\) where \ (L\) is the latent heat coefficient.
- 13.3: Phase Change and Latent Heat
The heat Q required to change the phase of a sample of mass...
- 13.3: Phase Change and Latent Heat
The latent heat of fusion is the amount of heat needed to cause a phase change between solid and liquid. The latent heat of vaporization is the amount of heat needed to cause a phase change between liquid and gas.
The heat Q required to change the phase of a sample of mass m is given by \(\mathrm{Q=mL_f}\) (melting or freezing) and \(\mathrm{Q=mL_v}\) (evaporating or condensing), where \(\mathrm{L_f}\) and \(\mathrm{L_v}\) are the latent heat of fusion and the latent heat of vaporization, respectively.
There is no temperature change until a phase change is complete. Latent heat is measured in units of J/kg. Both L f and L v depend on the substance, particularly on the strength of its molecular forces as noted earlier. L f and L v are collectively called latent heat coefficients.
Learning Objectives. Examine heat transfer. Calculate final temperature from heat transfer. So far we have discussed temperature change due to heat transfer. No temperature change occurs from heat transfer if ice melts and becomes liquid water (i.e., during a phase change).
Phase changes occur at fixed temperatures for a given substance at a given pressure, and these temperatures are called boiling and freezing (or melting) points. During phase changes, heat absorbed or released is given by: [latex] {Q=mL}, [/latex] where [latex] {L} [/latex] is the latent heat coefficient.
During phase changes, heat absorbed or released is given by: Q = mL where L is the latent heat coefficient.
