DYNAMIC EQUILIBRIUM

1. Reactions go to completion because their products are more stable and energetically favorable than the reactants.
2. Some reactions do not occure at all because the reactants are more stable than the products that would be formed or the activation energy threshold to start the reaction is too high.
3. In equilibrium reactions, the stability of the products and the reactants are similar in magnitude. For this reason, the reaction may be reversible.
4. In a reversible reaction, DYNAMIC EQUILIBRIUM occurs when the forward reaction and the reverse reaction occurs at the same rate.
   

**A good way to remember the basics of equilibrium is to think of the Hydrologic Cycle (or the Water Cycle). Water is in constant motion. The movement and endless recycling of water between the atmosphere, the land surface, and underground is called the hydrologic cycle, and has the basic concepts of equilibrium.

Click on the link below for a video demonstration of equilibrium!

http://www.youtube.com/watch?v=LBjRDF4XV8Q

(Summary of video, as described by original poster: Professor Harman explains the concept of equilibrium. In a dynamic equilibrium, though appearing static at the acroscopic level, the forward reaction equals the reverse reaction. To create this type of equilibrium, the system must be closed. This can occur in a chemical system, as well. In chemical equilibrium, the forward and reverse reactions are equal and the concentrations of products and reactants do not change. Professor Harman also explains how you can determine the direction of equilibrium mathematically. To do this, you can look at the partial pressures. As the pressures level out, the system reaches equilibrium. You can also look at the rates of the forward and reverse reactions. When the rates become equal, the system has reached equilibrium. Then, Professor Harman explains that if the equilibrium is disrupted, a new equilibrium will establish in which the overall ratios pf products and reactants are equal. These ratios help to determine the Equilibrium Constant, which reveals the direction of the overall balance of the chemical system.)

Click on the link below for an internet quiz on Chemical Equilibrium!

http://www.chemistry.nmsu.edu/studntres/chem116/resources/quiz_equilibrium.html

ESSENTIAL DEFINITIONS

(As you read through the material, if you come across a word you don't remember, refer to this list!)

Dynamic Equilibrium:

1. A state of balance achieved by two forces in motion; also, a state of apparent repose between two reactions going in opposite directions at equal speed
2. An equilibrium in which processes occur continuously, with no net change.
3. When two (or more) processes occur at the same rate so that no net change occurs.

Equilibrium Constant:

1. A quantity that characterizes the position of equilibrium for a reversible reaction; its magnitude is equal to the mass action expression at equilibrium. (Shown by the letter K). K varies with temperature.
   

Forward Reactions:

1. Forward reaction is a reaction in which products are produced from reactants and it goes from left to right in a reversible reaction.

Reverse Reactions:

1. A chemical equation in which the products of a forward reaction have become the reactants, and the reactants of the forward reaction are now the products.

Chemical Equilibrium:

1. The products of a reaction can go in reverse creating an equaling out of products and reactants.
   

Phase Equilibrium:

1. Exists between the solid and liquid phase of a substance
2. The point at which both the liquid and the solid exist at the same time (e.g. ice in water)

Solution Equilibrium:

1. The point at which both the dissolved solute and the re-crystallized form are present (e.g. sugar in water)

STP (Standard Temperature and Pressure):

1. Used to describe a substance at standard pressure (1 atm) and a temperature of 25°C (298.15 K).