Heat

Heat (abbreviated Q, also called heat change) is the transfer of thermal energy between two bodies which are at different temperatures. The SI unit for heat is the joule.

Changes of phase

A boiling pot of water, at sea level and normal atmospheric pressure, will always be at 100 °C no matter how much heat is added. The extra heat changes the phase of the water from liquid into water vapor. The heat added to change the phase of a substance in this way is said to be "hidden," and thus it is called latent heat (from a Latin word for hidden). Latent heat is heat per unit mass necessary to change the state of a given substance. Thus:

Related Topics:
Water - Sea level - Water vapor - Latin

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:L = rac{Q}{Delta m} ,!

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and

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:Q = int_{M_0}^{M} L,dm ,!

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where M_o is the amount of mass initially in the new phase, and M is the amount of mass that ends up in the new phase.

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L generally doesn't depend on the amount of mass that changes phase, so the equation can normally be written:

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:Q = LDelta m ,!

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Sometimes L can be time-dependent if pressure and volume are time-varying, so that the integral can be handled:

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:Q = int Lrac{dm}{dt}dt ,!

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someone check the above, please, to see if the latent heat really depends on where on the (P, V, T) curve the transition is taking place.

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