Enthalpy of mixing

The heat of mixing hE (also known as enthalpy of mixing or excess Gibbs ) is the heat that occurs when mixing pure chemical substances:

• If the mixture is heat absorbed by the mixed substances from the environment, so it is an endothermic curve.
• If the mixture is heat emitted by the mixed materials into the environment, it is an exotherm

This article is with the formula sign hE is the molar heat of mixing meant that the heat of mixing per mole.

Examples

Depending on the mixture components, the mixing of chloroform exothermic or endothermic run ( all sample data for about 25 ° C. ):

• Mixing with tetrahydrofuran is highly exothermic (about -2800 J / mol).
• The mixing with ethanol runs depending on your source material quantity either exothermic ( 20 mol% of chloroform and 80 mol % ethanol: about -400 J / mole)
• Or endothermic (20 mole - % ethanol and 80% by mole of chloroform: about 700 J / mol)

• Enthalpies of mixing at T = 25 ° C

Exo - and endothermic heat of mixing chloroform / ethanol

Endothermic heat of mixing chloroform / cyclohexane

Modeling

Heat of mixing curves binary mixtures at a given temperature can (RK ) and a sum symmetric functions ( SSF) are in accordance with equations Redlich - Kister described. Both expansions are based on the following simple relationship that is sufficiently accurate only for a few systems, however:

With

• ,: Mole fractions of the two components
• : Constant.

Redlich - Kister

With

• Ai: tunable parameter
• N = 1 .6 ( one to six parameter).

Sum symmetric functions

With

• Ai, ai: customizable parameters
• M = 1 .3 (two, four or six parameters).