Comparison with Enthalpy and Entropy

2 Gibbs Energy Diagrams for Pressure-Driven Phase Changes 

It is instructive to make up a g-P diagram for a pressure-driven phase change, as shown below. 

FIGURE 4.9 Comparison of the calculated enthalpy, entropy, and Gibb s energy, asafunctionof temperature, for water at temperatures near 100°C, all at a pressure of 1 bar (0.987 atm). The points are data from [2]. The entropy plot uses values directly from the table. The Gibbs energy plot uses absolute entropies, where absoiutE isteam table + 3.515 kJ/(kg K) and stcam-tablc enthalpies, relative to /j = 0 for liquid water at the triple point. 

Example 4.2 Construct a Gibbs energy-pressure diagram for the graphite-diamond system at 25°C, using the data in Table 4.A. 

From Eq. 4.33 we know that the slopes of the curves dg/dP)j are equal to the specific volumes v. So, for example, for graphite at 25°C 

---