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• Vaporizing a liquid involves an input of energy to increase the separation between molecules. Here, the latent heat involves a change in internal energy, plus work in expanding the volume. Examples of latent heats: material fusion, L f (J / kg) vaporization, L v (J / kg) water 33.5 x 104 22.6 x 105 ethyl alcohol 10.8 x 104 8.55 x 105
Q = m L f (for melting/freezing), Q = m L v (for vaporization/condensation), where L f is the latent heat of fusion, and L v is the latent heat of vaporization. The latent heat of fusion is the amount of heat needed to cause a phase change between solid and liquid.
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.
Explain the construction and use of a typical phase diagram. Use phase diagrams to identify stable phases at given temperatures and pressures, and to describe phase transitions resulting from changes in these properties. Describe the supercritical fluid phase of matter.
There is no temperature change until a phase change is complete. Latent heat is measured in units of J/kg. Both \(L_{\mathrm{f}}\) and \(L_{\mathrm{v}}\) depend on the substance, particularly on the strength of its molecular forces as noted earlier. \(L_{\mathrm{f}}\) and \(L_{\mathrm{v}}\) are collectively called latent heat coefficients.
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.
If heat were added at a constant rate to a mass of ice to take it through its phase changes to liquid water and then to steam, the energies required to accomplish the phase changes (called the latent heat of fusion and latent heat of vaporization) would lead to plateaus in the temperature vs time graph.
