# Enthalpy and ratio of slopes and graph

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1. Consider the phase change:

C(graphite) <---> C(diamond)

Given that delta_rG^o/Jmol^-1 = 1895 + 3.363T, calculate the enthalpy and entropy. Calculate the pressure at which diamond and graphite are in equilibrium with each other at 25 degree Celsius. Take the density of diamond and graphite to be 3.51 g/cm^3 and 2.25 g/cm^3, respectively. Assume that both diamond and graphite are in-compressible.

2. a. The vapor pressure of solid and liquid hydrogen iodide can be expressed empirically as

ln(P/torr) = -2906K/T + 19.020

and

ln(P/torr) = -2595.7K/T + 17.572

calculate the ratio of the slopes of the solid-gas curve and the liquid-gas curve at the triple point.

b. Given that the normal melting point, critical temperature, and the critical pressure of hydrogen iodide are 222K, 424 K, and 82.0 atm, respectively, use the data in part a is sketch the phase diagram of hydrogen iodide.

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##### Solution Summary

The enthalpy and entropy are calculated for T-dependent equations. The ratio of slopes from Clausiuis-Clayperon equations and phase diagrams are explained.

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