Abstract
A transition heat is the most important characteristics of first-order phase transitions. Black [1] was first who discovered in 1762 that in the transfer of water to vapor, some quantity of heat is absorbed, which he termed the latent evaporation heat. In spite of more than the two-hundred-year period of the heat transfer concept existence there are no analytical expressions relating the transition heat with other parameters of phase transitions. For example, the fundamental Physics Encyclopedia, articles devoted to the transition heat, evaporation heat, and so on, comprises no formulae but only tables of experimental data. One can also mention monographs [2-9] which have no relationships except for the conventional definition of the transition heat λ=TΔS. Hence, obtaining the relationships between the transition heat and other parameters of first-order phase transitions will be a substantial contribution into the theory of first-order phase transitions.
Highlights
A transition heat is the most important characteristics of first-order phase transitions
The transition heat is expressed in terms of the entropy variation ∆S, which cannot be measured experimentally
The transition heat is defined as λ=T∆S+A
Summary
General expressions for the transition heat of first-order phase transitions: The conventional expression for a transition heat λ=T∆S has two substantial drawbacks. In some phase transitions, for example, in evaporation, entropy changes but a system does the work, which can only be supplied by an external source of heat. The transition heat is expressed in terms of the entropy variation ∆S, which cannot be measured experimentally. The transition heat is defined as λ=T∆S+A. Where T is the transition temperature in K0, ∆S is the change of system entropy, A is the work that the system does. Entropy is calculated from the general definition [3]. The general expression for the heat for a phase transition has the form:. The volumes of phase spaces and the expressions for the work are specified for each particular phase transition. Approximate calculation of the phase space volumes for liquid and gaseous states.
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