The excess function/property provides the deviation from ideal behavior of a liquid or gas mixture. It can also inform about the type molecular interactions, i.e., attraction or repulsion, related to the the state of pure compounds before mixing. As as example, if a liquid mixture present an excess molar volume greater than 0, it can be said that the molecules of these compounds repulse each other when mixed.
For mixing: yes, in the ideal case we have DeltaHmixing and/or Hex = zero.
For reaction: we will have DeltaHmixing and DeltaHreaction. DeltaHreaction > 0 for endo, and < 0 for exothermic reactions (but also, it depends on what system you choose).
Hi.
Ideal behavior of a thermodynamic mixture reflects only the relative amounts of the constituents plus the entropy of mixing. (Amounts in moles plus mole fraction for small molecules, or moles plus volume fraction if polymers are involved, as given by the Flory Huggins theory for instance). One problem with this is that all solutes would have the same solubility in all solvents on a mole fraction or volume fraction basis.
Real mixtures deviate from the ideal mixture behavior by introducing excess thermodynamic properties. In mixtures, this is most typically due to interactions between the solute and solvent. If expressed in terms of the interaction parameter, then the deviation is incorporated into an excess enthalpy of mixing (which is basically just a name for the additional contribution to the enthalpy due to interactions). Just as a comment, this is also commonly written as an activity coefficient, which is just an different term derived from the excess enthalpy by an algebraic rearrangement of the equations for the excess enthalpy of mixing.
Hope this helps!
The difference between the thermodynamic function of mixing for a real system and the corresponding value for an ideal system at the same temperature and pressure is termed as the thermodynamic excess function and is usually denoted by the superscript E with the property under consideration.
The sign and magnitude of the excess properties gives an indication of nature and the extent of the intermolecular interaction.
it will really help if I get to know why delta V(mixing) for ideal case is zero and then V(excess) = del V(mixing)
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