Application of the Gibbs Phase Rule

In Chapter 13 we will consider the reaction equilibrium when styrene is hydrogenated to form ethylbenzene. Depending on the temperature and pressure of the system, this reaction may take place in the vapor phase or in a vapor-liquid mixture. Show that the system has three degrees of freedom if a single phase exists, but only two degrees of freedom if the reactants and products form a two-phase mixture.

Question

Application of the Gibbs Phase Rule

In Chapter 13 we will consider the reaction equilibrium when styrene is hydrogenated to form ethylbenzene. Depending on the temperature and pressure of the system, this reaction may take place in the vapor phase or in a vapor-liquid mixture. Show that the system has three degrees of freedom if a single phase exists, but only two degrees of freedom if the reactants and products form a two-phase mixture.

Accepted Answer

The styrene-hydrogen-ethylbenzene system is a three-component (C = 3), single-reaction (M= 1) system. Thus

[latex]F = C - M - P +2=4- P[/latex]

Clearly, if only the vapor phase exists (P = 1), there are three degrees of freedom; if, however, both the vapor and liquid are present (P = 2), the system has only two degrees of freedom.

Question 8.9.1: Application of the Gibbs Phase Rule In Chapter 13 we will co...

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