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The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
Jacobus van 't Hoff found a quantitative relationship between osmotic pressure and solute concentration, expressed in the following equation: Π = i c R T {\displaystyle \Pi =icRT} where Π {\displaystyle \Pi } is osmotic pressure, i is the dimensionless van 't Hoff index , c is the molar concentration of solute, R is the ideal gas constant ...
The van 't Hoff factor i (named after Dutch chemist Jacobus Henricus van 't Hoff) is a measure of the effect of a solute on colligative properties such as osmotic pressure, relative lowering in vapor pressure, boiling-point elevation and freezing-point depression.
In 1884, Jacobus van 't Hoff proposed the Van 't Hoff equation describing the temperature dependence of the equilibrium constant for a reversible reaction: = where ΔU is the change in internal energy, K is the equilibrium constant of the reaction, R is the universal gas constant, and T is thermodynamic temperature.
This equation can be used to calculate the value of log K at a temperature, T 2, knowing the value at temperature T 1. The van 't Hoff equation also shows that, for an exothermic reaction (<), when temperature increases K decreases and when temperature decreases K increases, in accordance with Le Chatelier's principle.
The enthalpy of reaction is then found from the van 't Hoff equation as = . A closely related technique is the use of an electroanalytical voltaic cell , which can be used to measure the Gibbs energy for certain reactions as a function of temperature, yielding K e q ( T ) {\displaystyle K_{\mathrm {eq} }(T)} and thereby Δ rxn H ⊖ ...
The van 't Hoff equation relates the change of solubility equilibrium constant (K sp) to temperature change and to reaction enthalpy change. For most solids and liquids, their solubility increases with temperature because their dissolution reaction is endothermic (ΔH > 0). [12]
Despite the limitations of this derivation, the equilibrium constant for a reaction is indeed a constant, independent of the activities of the various species involved, though it does depend on temperature as observed by the van 't Hoff equation.