1. Reactions move in both directions.
2. Equilibrium is the point at which the rate of forward reaction is equal to the rate of reverse reaction.

The equilibrium expression is a ratio between the product and the reactant.

eg. for H₂ + I₂ <=> 2HI

The Equilibrium expression represents tre final ratio between the two:

[HI]² / [H₂][I₂]

1. If temperature increases the reaction will shift in the endothermic direction (taking in heat).
2. If temperature decreases the reaction will shift in the exothermic direction.