where is the latent heat per mole, and the molar volume. Let refer to the liquid (or solid) phase, and to the vapor. It follows that

(9.76) |

because the vapor is much less dense than the liquid, so that . Let us also assume that the vapor can be adequately treated as an ideal gas, so that its equation of state is written

(9.77) |

Thus, , and Equation (9.75) becomes

(9.78) |

Assuming that is approximately temperature independent, we can integrate the previous equation to give

(9.79) |

which implies that

(9.80) |

where is some constant. This result shows that the vapor pressure, , is a very rapidly increasing function of the temperature, .