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1_The_properties_of_mixtures_final

# 1_The_properties_of_mixtures_final - Properties of...

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Chem 300 Properties of Mixtures (nonelectrolyte solutions)

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Partial molar properties Partial pressure – contribution of one component to the total pressure – is used to discuss the properties of mixtures of gases. For more general description of the thermodynamics of mixtures we need to introduce other “partial” properties. A partial molar property is the contribution per mole that a substance makes to an overall property of a mixture.
V m,water V m,EtOH Partial molar volume Real solution: Molar volume of ethanol: 0.058L Molar volume of water: 0.018L Combined volume: 0.036L (half mole of each) In real solution the partial volume affected by the presence of other component In an ideal solution the volume of a mixture should be equal to the sum of the volumes of the individual components.

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Water/ethanol mixture The less ideal the solution is, the greater the partial molar volumes deviate from linearity. V m , water V m,EtOH
Can partial molar volumes be negative? The change in volume upon changing the composition of the mixture can be determined using the partial molar volumes of the two species. If the addition of component B causes the total volume of the solution to decrease, its partial molar volume is negative. Can this occur in an ideal solution? dV = V m , A dn A + V m , B dn B

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Partial molar Gibbs energies and chemical potential The chemical potential, μ i , provides criteria for equilibrium and spontaneity for a multi- component system. Transfer of component i from state A to state B G m , i = G n i T , p , n j = μ i dG = μ i B dn i μ i A dn i = μ i B μ i A ( ) dn i
Effect of pressure on chemical potential The higher the partial pressure the more chemically active the species is. The chemical potential reflects the natural tendency of the species to react plus the effect that being at a pressure other than 1 bar has on the reactivity. G m = G m o + RT ln p / p o μ j = μ j o + RT ln p j / p o RT

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Mixtures (perfect gas) You can use chemical potential to develop the equation for G of mixing we discussed in Chapter 4. Mix n A moles of gas A with n B moles of gas B at the same T and P (ideal gas).
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1_The_properties_of_mixtures_final - Properties of...

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