13.1 The solution properties Solutions is a homogeneous mixture of two or more substances Ability of substance to form solutions depends on two general factors: Intermolecular interaction natural tendency of substances to spread into larger volumes Depending on the original states solutions are of six types:

The effect of intermolecular forces Intermolecular attractions play a central role in the information of solutions There are three types interactions: Solvent-solvent interaction Solute-solute interaction Solvent-solute interaction Interaction between solute and solvent molecules are known solvation Interaction between solute and water molecules are known hydration

Heat of solution, Hsoln = H1 + H2 + H3 Separation of solute molecules Separation of solvent molecules Formation of solute-solvent interactions Heat of solution, Hsoln = H1 + H2 + H3 Solute-solvent > solvent-solvent + solute-solute, exothermic Solute-solvent < solvent-solvent + solute-solute, endothermic

Enthalpy changes accompanying the solution process Hsoln < 0 Enthalpy Hsoln > 0

Solution formation, spontaneity and entropy (b) Increasing randomness in a solution process The degree of randomness in the system, sometimes referred to as disorder, is given by a thermodynamic quantity called entropy Processes occurring at a constant temperature in which the randomness or dispersal in space (entropy) of the system increases tend to occur spontaneously In most of the cases the formation of solutions is favored by the increase in entropy that accompanies mixing

Solution formation and chemical reactions (a) Nickel metal and HCl (b) Nickel reacts slowly with HCl, forming NiCl2 (aq) and H2(g) (b) NiCl2.6H2O is obtained when the soln is evaporated The nickel-acid reaction is not a simple dissolution Ni(s) + 2HCl(aq) NiCl(aq) + H2(g)

NaSO4(s) + 10H2O(g) NaSO4.10H2O(g) Essentially all of the water vapor in the closed container is consumed in this reaction. If we consider our system to consist initially of NaSO4(s) and 10H2O(g), (a) does the system become more or less ordered in this process, and (b) does the entropy of the system increase or decrease? (a) Initially the water vapor is dispersed throughout the entire volume then it is confined to the NaSO4.10H2O(s) lattice, means it becomes less dispersed or more ordered (b) Its entropy is decreased