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Explain changes in heat during changes of state, and describe latent heats of fusion and vaporization; Solve problems involving thermal energy changes when heating and cooling substances with phase changes
The heat \(Q\) required to change the phase of a sample of mass \(m\) is given by \[ Q = mL_f (melting/freezing),\] \[Q = mL_v (vaporization/condensation),\] where the latent heat of fusion, \(L_f\), and latent heat of vaporization, \(L_v\), are material constants that are determined experimentally.
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.
Learn Latent Heat & Phase Changes with free step-by-step video explanations and practice problems by experienced tutors.
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.
We examine the effects of phase change more precisely by considering adding heat into a sample of ice at −20ºC (Figure 3). The temperature of the ice rises linearly, absorbing heat at a constant rate of 0.50 cal/g⋅ºC until it reaches 0ºC.
1 Comment. Was this helpful? 22. Video transcript. Hey, guys. So in previous videos, we talked about the specific heat and how that heat dealt with temperature changes. In this video, we're going to talk about latent heats and how those deal with phase changes in a material.
