Question

How does \(\Delta H_{\text {soln }}\) relate to deviations from Raoult's law? Explain.

Short answer

The enthalpy of solution, ΔH_soln, relates to deviations from Raoult's law based on the strength of solute-solvent interactions in a mixture compared to their pure state interactions. Positive deviations from Raoult's law occur when solute-solvent interactions are weaker, resulting in a positive ΔH_soln indicating heat absorption during solution formation. Negative deviations occur when solute-solvent interactions are stronger, resulting in a negative ΔH_soln indicating heat release during solution formation.

Step-by-step solution

Define Raoult's law and its deviations

Raoult's law states that the partial vapor pressure of each component in a mixture is proportional to its mole fraction in the solution. Mathematically, for a component A in a mixture, it can be represented as: \(P_A = x_A * P_A^*\) where \(P_A\) is the partial vapor pressure of component A, \(x_A\) represents the mole fraction of A in the solution, and \(P_A^*\) is the vapor pressure of the pure component A. Deviations from Raoult's law occur when the interactions between the components in a mixture are significantly different from their interactions in the pure state. The deviation can be either positive (positive deviation) or negative (negative deviation).

Define enthalpy of solution, ΔH_soln

The enthalpy of solution, represented by ΔH_soln, is the heat absorbed or released when a solute is dissolved in a solvent. In simple terms, it is a measure of the energy change associated with the process of forming a solution. The ΔH_soln for a mixture can have different values depending on if the dissolution is endothermic (heat is absorbed) or exothermic (heat is released).

Explain the relationship between ΔH_soln and deviations from Raoult's law

The relationship between ΔH_soln and deviations from Raoult's law can be understood by examining the interactions between the components in the mixture. - In the case of positive deviation from Raoult's law, the partial vapor pressure of the components is higher than that predicted by Raoult's law. This would mean that the solute-solvent interactions in the mixture are weaker than the solute-solute and solvent-solvent interactions in their pure states. Consequently, the ΔH_soln in this case will be positive, indicating that heat is absorbed during the solution formation. - On the other hand, in the case of negative deviation from Raoult's law, the partial vapor pressure of the components is lower than that predicted by Raoult's law. This would mean that the solute-solvent interactions in the mixture are stronger than the solute-solute and solvent-solvent interactions in their pure states. In this case, the ΔH_soln will be negative, indicating that heat is released during the solution formation. In summary, the enthalpy of solution, ΔH_soln, is related to deviations from Raoult's law, as positive deviations are associated with endothermic dissolution processes, while negative deviations are associated with exothermic dissolution processes. This relationship stems from the strength of solute-solvent interactions in the mixture as compared to the pure state interactions.