Chemical Equilibrium Chapter 11

The term equilibrium is a term that implies a balancing of some kind The term equilibrium is a term that implies a balancing of some kind. Equilibrium is found all around us and it may be physical or chemical. A person sitting on a chair is in equilibrium with the floor. A carbonated drink is in a state of equilibrium.

Chemical Equilibrium Most reactions do not go to completion. After some time enough products have accumulated to slow the reaction down. The forward reaction will stop and the reverse reaction will begin. When the rate of the forward reaction and the reverse reaction are equal, we have equilibrium.

A system is at equilibrium when it meets the 4 following criteria: The system is a CLOSED system. This means that there are NO reactants or products leaving or entering the system. The temperature is CONSTANT. There are no macroscopic activity, meaning that COLOR, PRESSURE and CONCENTRATION are constant. There is molecular activity. (microscopic level)

DEFINITIONS An OPEN SYSTEM is a system in which reactants can enter and products can leave. Ex: A pan of water boiling on a stove. Sometimes a system may seem to be at equilibrium but it does not meet the 4 above criteria. This means the system is called a STEADY STATE system.

Equilibrium Constant aA + bB cC + dD Keq = [C] c [D] d This is called the Equilibrium law The larger the Keq value, the more the reaction favors the products. The units used are mol/L for concentration.

PRACTICE PROBLEMS Textbook p. 318 # 1- 4