Editing Density (section)

== Density of solutions ==
The density of a [[Solution (chemistry)|solution]] is the sum of [[mass concentration (chemistry)|mass (massic) concentrations]] of the components of that solution.

Mass (massic) concentration of each given component <math>\rho_i</math> in a solution sums to density of the solution,
<math display=block>\rho = \sum_i \rho_i .</math>

Expressed as a function of the densities of pure components of the mixture and their [[volume concentration|volume participation]], it allows the determination of [[excess molar quantity|excess molar volumes]]:
<math display=block>\rho = \sum_i \rho_i \frac{V_i}{V}\, = \sum_i \rho_i \varphi_i = \sum_i \rho_i \frac{V_i}{\sum_i V_i + \sum_i {V^E}_i},</math>
provided that there is no interaction between the components.

Knowing the relation between excess volumes and activity coefficients of the  components, one can determine the activity coefficients:
<math display=block>\overline{V^E}_i = RT \frac{\partial\ln\gamma_i}{\partial P}.</math>