CHEM 108 1st Edition Lecture 7 Current LectureChapter 11 Solutions: Properties and Behavior:Solutions:- A solution is composed of two parts: the solute and the solvent.o Solute: In the case of a solution of a gas or solid dissolved in a liquid, is the gas orsolid; in other cases, the solute is the component in smaller amount. o Solvent: In a solution of a gas or solid dissolved in a liquid, is the liquid; in other cases, the solvent is the component in greater amount.- The solubility of a solute is the amount that dissolves in a given quantity of solvent at a given temperature. o The solubility of one substance in another depends on two factors – nature’s tendency toward mixing, and the types of intermolecular attractive forces, such as the polarity of the substances. Remember like dissolves in like, which basically means polar dissolves in polar or anything with partial charge, and non-polar dissolves in non-polar.o A saturated solution is in equilibrium with respect to the amount of dissolved solute. The rate at which the solute leaves the solid state equals the rate at whichthe solute returns to the solid state.o An unsaturated solution is just one that is not in equilibrium, and more can be dissolved in that solutiono A supersaturated solution is a solution that contains more dissolved substance than a saturated solution does. This occurs when a solution is prepared at a higher temperature and is then cooled. This is a very unstable situation, so any disturbance causes precipitation, such as “seeding” with a crystal.- Solubility of gases: o The solubility of a gas in a liquid depends on all the factors that influence the gas,such as temperature and pressure. As temperature increases the molecules of gas have more kinetic energy which overcomes the solute-solvent interactions and decreases the solubility of the gas in a liquid. As partial pressure of the gas increases the solubility of gas increases too. This is the case because with pressure increasing the number of collisions with the fluid increase to. This observation is mathematically expressed by henry’s law Cgas= kh*Pgas where C is concentration (solubility) of the gas, k is a constant and P is partial pressure of the gas. Partial pressure of gas = mole fraction of gas* total pressure (atmosphericpressure)Solubility curves:- In most cases, solubility increases with increasing temperature. However, for a number of compounds, solubility decreases with increasing temperature. This is explained by thedifferences in heat of solution.- When dissolving absorbs heat (is endothermic), the temperature of the solution decreases as the solute dissolves. The solubility will increase as temperature increases. Cold packs use this type of solution. - When dissolving releases heat (is exothermic), the temperature of the solution increasesas the solute dissolves. The solubility will decrease as temperature increases. Hot packs use this type of solution-- The slope of the lines is where the solution is saturated.Vapor pressure:- Pressure exerted by a gas in equilibrium with its liquid, when rates of evaporation and condensation are equal (Dynamic equilibrium)- A system in dynamic equilibrium can respond to changes in the conditions o Temperature: • Higher temperature = higher kinetic energy; more molecules with sufficient Ek to overcome attractive forces in liquid phase. o Surface Area: • Higher surface area = greater number of molecules in position to enter gas phase. o Intermolecular Forces: • Stronger forces = higher Ek needed to enter gas phase.- In general, vapor pressure of solution is lower than vapor pressure of pure solvent.- Raoult’s Law:o Vapor pressure of solution is proportional to mole fraction of solvent (non-volatile solute). o Psolution = Xsolvent * Psolvent Where x is the mole fraction of the solvento Ideal Solutions are solutions that obey Raoult’s Law.- Colligative Properties: Solution properties that depend on concentration of solute particles, not the identity of
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