Notion of Activity in Chemistry

Jean-Louis Burgot is a retired Professor of analytical chemistry in Rennes, France.

• 1st  part: The Activity in Classical Thermodynamics.- Thermodynamic systems.- Gibbs and Helmhotz energies.- Escaping tendency and molar Gibbs energy.- Partial molar properties.- Chemical potential or partial molar Gibbs energy.- An overview of the notion of activity.- The concept of fugacity.- Ideal solutions.- Definitions of the activity.- Activity of a gaz.- Activities of non- electrolytes in solutions.- Activities of electrolytes: definitions.- Determination of the activity of non-electrolytes.- Determination of the activity of electrolytes.- Debye and Hückel ‘s relations.- Excess Gibbs energies and activities.- Chemical  equilibrium  constants : activities and  Gibbs energies of reactions.- Derivation of thermodynamic equilibrium constants- pH and its measure.- General principles of calculations of ionic species concentrations in solutions involving  activities .- 2nd  part: The Activity in Statistical Thermodynamics.- Statistical thermodynamics in brief.- Concept of ensembles and postulates.- The canonical ensemble: notion of distribution.- Thermodynamic quantities in the framework of the canonical ensemble.- Other ensembles .- Systems of molecules and subsystems  independent  distinguishable and      “indistinguishable”.- Perfect gases.- Classical statistical mechanics- Notion of configuration –  Classical canonical partition function.- The configurational  partition function – Molecular distribution functions.- The radial distribution function.- Radial distribution function and  thermodynamic quantities- calculations of the internal energy and of the pressure of a system.- Radial distribution function and calculation of the isothermal compressibility coefficient of a system.- The chemical potential and the radial distribution function: General formal introduction of the activity and  of the  activity coefficient.- Imperfect gases – The virial coefficients in terms of interaction potential energies.- A statistical  expression of the activity: A relation between it and the concentration in the case of an imperfect gaz.- Activities of gases in a mixture of imperfect gases.- Chemical equilibria between  gases and statistical thermodynamics.- Activity coefficients of gases.- Activities and concentrations of non-electrolytes in dilute liquid solutions – McMillan- Mayer’s theory of their osmotic pressure.- A study of dilute solutions of non-electrolytes  at constant pressure and temperature.- The activity coefficients of solutes in binary non-electrolyte solutions.- Molecular distribution functions in binary mixtures.- The  Kirkwood-Buff’s theory- Changes of chemical potentials of solutes with their concentrations at constant pressure and temperature.- Expressions of the chemical potentials of the components of ideal solutions of  non-electrolytes.