Chap_13revA - Chapter 13 Solutions Solutions are...

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Unformatted text preview: Chapter 13: Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed uniformly throughout the solvent. How Does a Solution Form? Intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles. As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them. How Does a Solution Form? If an ionic salt is soluble in water, it is because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal. Energy Changes in Solution 3 processes: Separation of solute particles Separation of solvent particles New interactions between solute and solvent Energy Changes in Solution The enthalpy change of the overall process depends on H for each of these steps. Why Do Endothermic Processes Occur? Processes do not occur spontaneously unless the energy of the system is lowered. Why Do Endothermic Processes Occur? Yet we know that in some processes, like the dissolution of NH4NO3 in water, heat is absorbed, not released. Enthalpy Is Only Part of the Picture The reason is that increasing the disorder or randomness (known as entropy) of a system tends to lower the energy of the system. Enthalpy Is Only Part of the Picture Even though enthalpy may increase, the overall energy of the system can still decrease if the system becomes more disordered. ...
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