Chemical Potential: Summary
Key points from this module:
- For a pure material, the chemical potential is the same as the Gibbs-free energy.
- The chemical potential is an intensive variable.
- Typical units of chemical potential are kJ/mol. Chemical potential does not have an absolute value, but depends on the conditions chosen as a reference.
- Chemical potential is the driving force for mass transfer. Species move from high chemical potential to low chemical potential. At phase equilibrium, the chemical potential for a given species is the same in each phase.
- The phase with the lowest chemical potential for a single component is the stable phase.
- When salt is dissolved in a liquid, the chemical potential of the liquid decreases. As a result, the melting temperature decreases and the boiling temperature increases.
- The slope of the chemical potential versus temperature for a single component is the negative of the specific entropy of the phase.
- The slope of chemical potential versus pressure for a single component is the specific volume of the phase.
From studying this module, you should now be able to:
- Explain what chemical potential is.
- Determine which phase is more stable, given plots of chemical potentials versus temperature or pressure for a pure component.
- Explain, using chemical potential, why adding salt to water lowers its melting point and raises its boiling point.
- Explain why increasing the pressure melts ice, but increasing the pressure makes solid ethanol more stable.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder