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CHMA11H3 (64)
Chapter 12

Chapter 12

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University of Toronto Scarborough
Jamie Donaldson

Chapter 12 12.1 Thirsty Solutions: Why You Should Not Drink Water Seawater actually draws water out of the body as it passes through the stomach and intestines, resulting in diarrhoea and further dehydration Thirsty Solution, is a solution that draws water to itself it has a tendency to mix Solution is a homogenous mixture of two or more substances or components. The majority component is usually called the solvent and the minority component is called the solute The reason water draws water to itself is related to natures tendency toward spontaneous mixing Unless it is highly unfavourable energetically, substance tend to combine into uniform mixtures, not separate into pure substances The tendency toward mixing results in a uniform concentration of the final solution 12.2 Types of Solution and Solubility A solution may be composed of a solid and a liquid but may also be composed of a gas and a liquid Aqueous Solutions is a solution in which water is the solvent and a solid, liquid, or gas is the solute Solubility is the amount of the substance that will dissolve in a given amount of solvent Many physical system tend to lower the potential energy The formation of a solution does not necessarily lower the potential energy of its constituent particles We cannot think of the mixing of two idea gases as lowering their potential energy, the tendency to mix is related to a concept called entropy Entropy is a measure of energy randomization or energy dispersal in a system The pervasive tendency for energy to spread out, or disperse, whenever it is not restrained from doing so is the reason that two ideal gases mix www.notesolution.com The tendency for energy to disperse is why thermal energy flows from the hot end of the rod to the cold one, and not the other way around In the absence of intermolecular forces, two substances spontaneously mix to form a homogenous solution -Solvent-solute interactions: the interactions between a solvent particle and a solute particle -Solvent-solvent interactions: the interactions between a solvent particle and another solvent particle -Solute-solute interactions: the interactions between a solute particle and another solute particle All three interactions are of similar magnitude so the two substances are soluble in each other in all proportions they are said to be miscible The formation of the solution is driven by the tendency toward mixing, or toward greater entropy If solvent molecules and solute molecules each interact more strongly with molecules of their own kind than with molecules of the other kind then a solution may still form, depending on the relative disparities between the interactions If the disparity is small, the tendency to mix results in the formation of a solution even though the process is energetically uphill If the disparity is large, however, a solution will not form Although the tendency to mix is strong it cannot overcome the large energy disparity between the powerful solvent-solvent interactions and the weak solvent-solute interactions 12.3 Energetics of Solution Formation The separation of the solute into its constituent particles is always endothermic because energy is required to over-come the forces that hold the solute together Separating the solvent particles from each other to make room for the solute particles, is also endothermic because energy is required to overcome the intermolecular forces among the solvent particles Mixing the solute particles with the solvent particles, is exothermic because energy is released as the solute particles interact with the solvent particles www.notesolution.com
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