Knightrises10
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Use the first law of thermodynamics to explain why specific latent heat of vaporisation is greater than fusion for a particular substance?
I do understand the reason, but how to explain in terms of first law of thermodynamics?
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lordaxil
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The first law of thermodynamics states that change in internal energy is equal to heat flow plus work done on the system: \Delta U = q + w. Since evaporation and melting are supposed to occur at constant temperature, then the work done by system against surroundings must come from a flow of heat into the system
q = \Delta U - w.
For evaporation, both 

 \Delta U (energy required to separate particles) and -w (the work done by the system against surroundings) are larger than for melting solid, as the particles have to be separated by larger distance in a gas than in liquid, and this requires a bigger volume change against external pressure.
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