9: Gibbs Free Energy
- Page ID
- 414068
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In this chapter, we will concentrate on chemical processes that happen at constant \(T\) and constant \(P\).1 As such, we will focus our attention on the Gibbs free energy.
- The majority of chemical reactions in a lab happens at those conditions, and all biological functions happen at those conditions as well.
- 9.1: Gibbs Equation
- Recalling from chapter 8, the definition of G is:
- 9.2: Temperature Dependence of ΔG
- Let’s analyze the first coefficient that gives the dependence of the Gibbs energy on temperature. Since this coefficient is equal to −S and the entropy is always positive, G must decrease when T increases at constant P and {ni}, and vice versa.
- 9.3: Pressure Dependence of ΔG
- We can now turn the attention to the second coefficient that gives how the Gibbs free energy changes when the pressure change. To do this, we put the system at constant T and {ni}, and then we consider infinitesimal variations of G.
- 9.4: Composition Dependence of ΔG
- The third and final coefficient gives the chemical potential as the dependence of G on the chemical composition at constant T and P. Similarly to the previous cases, we can take the definition of the coefficient and integrate it directly between the initial and final stages of a reaction.