Dynamic equilibrium is when the rate of the forward and reverse reactions are equal.  The reaction will appear to have stopped, as the concentrations of each species won’t change, but the reaction continues to proceed in both directions.

Equilibrium constants
Equilibrium constant expressions are the ratio of the concentrations of products to reactants using their coefficients from the balanced equation as exponents.  Pure solids and liquids are not included in the equilibrium constant expression.  Equilibrium concentrations are plugged into the expression to solve for the equilibrium constant.  A large equilibrium constant means that the reaction “lies to the right” with more products than reactants at equilibrium.  A small constant means that the reaction “lies to the left” with more reactants the products present at equilibrium.

Reaction Quotients
The reaction quotient is the value when concentrations at any time are plugged into the equilibrium constant expression.  If the reaction quotient equals the equilibrium constant, then the system is at equilibrium.  If the reaction quotient is too large, the reaction will proceed to the left to produce more reactants (and reduce products).  The opposite will happen if the reaction quotient is too small.

Solving equilibrium problems
A simple technique for solving equilibrium problems is the ICE chart method:

To solve the problem using the ICE chart:

Solubility equilibrium
The solubility equilibrium constant is written for a dissolution reaction (a solid compound dissociates when dissolved in water).  The pure solid reactant is not included in the expression.  A saturated solution is one that is at equilibrium. 

Le Chatelier’s Principle
Le Chatelier’s principle says that if a system at equilibrium is stressed or changed, the system will shift to reach equilibrium again.  Whatever you do to the system, it will un-do it.  For example, if you add more reactants, the reaction will proceed to the right to get rid of the extra reactants and make more products.

Flash Movie	Flash Game	Flash Card
Core Concept Tutorial	Problem Solving Drill	Review Cheat Sheet

Equilibrium is established when the rate of the forward reaction is equal to the rate of reaction of the reverse reaction in a reversible reaction.  This tutorial introduces how equilibrium is established, how equilibrium constant expressions are written and how equilibrium constants are calculated.  A problem solving technique for equilibrium problems will be illustrated in the examples.  The use of the reaction quotient to determine if a system is at equilibrium is illustrated.  Le Chatelier’s principle will be introduced, along with solubility equilibrium.

Specific Tutorial Features:

• Molecular animation of establishment of dynamic equilibrium
• Animation of equations to show a change in the ratio of product to reactants
• Use of “ICE Chart” problem solving technique for solving equilibrium problems
• Application of Le Chatelier’s principle to the manufacturing industry
• How do these questions look on the AP Exam?

 Series Features:

• Concept map showing inter-connections of new concepts in this tutorial and those previously introduced.
• Definition slides introduce terms as they are needed.
• Visual representation of concepts
• Animated examples—worked out step by step
• A concise summary is given at the conclusion of the tutorial.

• Dynamic equilibrium
• Equilibrium constant
  • Writing expressions
  • Calculating constants
  • Meaning of the equilibrium constant
• Reaction quotient
  • Writing expressions and finding the value
  • Using it to determine if it’s at equilibrium
• Solving equilibrium problems
  • Using the ICE chart
• Solubility equilibrium
• Le Chatelier’s principle