Solubility equilibrium Entropy & Free Energy Notes #8 Chapter 18.3-18.4

Outline Solubility Equilibrium Entropy and Free Energy Solubility Product Constants Finding the concentrations of ions in solution Common Ion Effect Entropy and Free Energy Free Energy and Spontaneous Reactions Enthalpy, Entropy, and Free Energy

Classes of Solubility for ionic compounds in water Classes: Soluble, Mostly Insoluble, Insoluble

Expressing Solubility equilibrium AgCl(s) Ag+(aq) + Cl-(aq) Equilibrium Expression: Keq = [Ag+] x [Cl-] [AgCl] Solubility Product Constant: ksp = keq x [AgCl] = [Ag+] x [Cl-] The smaller the numerical value of the solubility product constant, the lower the solubility of the compound.

Other Solubility product consants These constants will always be provided in a table for you. This is in your textbook.

PbCrO4(s) Pb+2(aq) + CrO4-2(aq)

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Common Ion Effect What if we mix two solutions, and they both share a common ion?? A common ion is an ion that is found in both salts in a solution The lowering of the solubility of an ionic compound as a result of the addition of a common ion is called the common ion effect.

Common Ion Effect A saturated solution of lead(II) chromate is pale yellow. When a few drops of lead nitrate are added to the solution, more lead(II) chromate precipitates.

Part 2: Entropy and Free Energy Inside a pile of oily rags or a stack of hay that has not been thoroughly dried, decomposition causes heat to build up. When heat cannot escape, the temperature can become high enough to cause a fire. You will learn about the conditions that will produce a spontaneous chemical reaction.

Spontaneous? A spontaneous reaction occurs naturally and favors the formation of products at the specified conditions. You don’t have to do anything! It happens automatically!

Non-spontaneous? A nonspontaneous reaction is a reaction that does not favor the formation of products at the specified conditions. Photosynthesis is a nonspontaneous reaction that requires an input of energy

Spontaneous Reactions Produce a great amount of products at equilibrium AND Release FREE ENERGY. Free Energy: Free energy is energy that is available to do work. (To be used to do something)

entropy Entropy is a measure of the disorder of a system. The law of disorder states that the natural tendency is for systems to move in the direction of maximum disorder or randomness.

Entropy and Spontaneity An increase in entropy favors the spontaneous chemical reaction; a decrease favors the nonspontaneous reaction. For a given substance, the entropy of the gas is greater than the entropy of the liquid or the solid. Similarly, the entropy of the liquid is greater than that of the solid.

How does entropy increase? 1) Entropy increases when a substance is divided into parts. 2) Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules. 3) As the temperature increases, the molecules move faster and faster, which increases the disorder/Entropy.

How do we know if a reaction is spontaneous. We must look at TWO things: 1) Enthalpy (Change in Heat) 2) Entropy (Amount of Disorder) The size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous; that is, whether it favors products and releases free energy.

Gibbs Free energy The Gibbs free-energy change is the maximum amount of energy that can be coupled to another process to do useful work. If ΔG is negative, it is a spontaneous reaction.

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