EQUILIBRIUM

Most reactions go forward and backward! Guess what… Most reactions go forward and backward!

These reversible reactions come to a chemical equilibrium.

Equilibrium Occurs when the rate of the forward reaction is equal to the rate of the backward reaction

Applications of Equilibrium: Phase Changes Saturated Solutions Acids/Bases Chemical Reactions

Occurs when the rate of the forward reaction is equal Equilibrium Occurs when the rate of the forward reaction is equal to the rate of the backward reaction

How fast or slow a reaction occurs Reaction Rate How fast or slow a reaction occurs

Molecules must collide in order to react Collision Theory Molecules must collide in order to react

Reactions with a HIGH Ea proceed at a SLOW rate.

2 HI  H2 + I2

Equilibrium Constant (Keq) A measure of how far a reaction goes to the right

[ ] = concentration

Keq > 1 More products than reactants Keq < 1 More reactants than products

Once a reaction reaches equilibrium can it ever change?? YES!!! All it takes is a change in either the forward or reverse rates.

(and therefore changes What changes rxn rate (and therefore changes the equilibrium): Concentration Pressure Temperature

Le Chatelier’s Principle If changes are made to a system in equilibrium, the RXN will shift in the direction that will reduce the change

Concentration If substance is added, the rxn will shift away from that side; If substance is removed, the rxn will shift towards that side

If pressure is increased, the rxn will shift to the side that will produce fewer molecules (compare moles of gas)

Increased temp will shift the rxn to the side that absorbs heat Temperature Increased temp will shift the rxn to the side that absorbs heat