Reaction Equilibrium

What are three applications of reaction equilibrium in reversible reactions?

1. Law of Mass Action
2. The equilibrium constant
3. Le Châtelier's Principle

What is the Law of Mass Action?

The Law of Mass Action states that a reaction rate is proportional to the product of the concentrations of the reactants.

What is the equilibrium constant ($K_{eq}$)?

A number that can determine the concentration of reactants or products when a chemical reaction is at equilibrium.

$K_{eq}$ is an extension of rate constants (k) detailed above but extends those concepts to reversible reactions where the rate of the forward reaction equals the rate of the reverse reaction.

For a given reversible reaction, what is the equilibrium constant?

$$% latex2html id marker 12293a A + b B \rightleftharpoons c... ...ward}}{K_{Reverse}} = \frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}\\$$ (37.1)

Note: Pure solids and liquids do not appear in the equilibrium constant expression.

What does the $K_{eq}$ reveal about the direction a reaction will proceed?

Table 36.2: $K_{eq}$ and the direction of a reaction.

$K_{eq} > 1$	Products favored
$K_{eq} = 1$	Neither products nor reactants favored
$K_{eq} < 1$	Reactants favored

Is temperature at all important for a $K_{eq}$?

YES!!!! A $K_{eq}$ is specific to a given reaction's environment at a given temperature.

Please don't forget this.

What is Le Châtelier's Principle?

In my humble opinion, probably the most profound principle proposed:

Principle 1   If a chemical system at equilibrium experiences a change in concentration, temperature, or total the equilibrium will shift in order to minimize that change.

In chemistry, Le Châtelier's principle could be seen at work the following ways:

Table 36.3: Applications of Le Châtelier's principle.

Concentration	Increasing the concentration of a substance will shift the equilibrium to the side that would reduce that change in concentration.
Temperature	For an exothermic reaction, if we were to lower the temperature, the equilibrium would shift in such as way as to produce heat.
	Conversely, for an endothermic reaction, if we were to raise the temperature, the equilibrium would shift to decrease the temperature.
Pressure	For example, in a system where gas exists in the product form (e.g. 4 moles) and reactant form (e.g. 2 moles), if an increase in total pressure occurs, then the equilibrium would shift to the side with the smaller amount of gas (the reactant side, i.e. 2 moles).