INTRODUCTION TO EQUILIBRIUM

Kinetics Explains how chemical reactions take place and some of the factors that affect the reactions’ speed Equilibrium when the rate of opposing forces are equal Remember equilibrium with respect to vapor pressure or dissolving

A few chemical reactions go to completion Using up one or more reactants and then stopping Many reactions behave a different way… aA + bB  cC + dD At first A and B start to form C and D But then, C and D start to react to form A and B cC + dD  aA + bB These two reactions proceed until the two rats of reaction become equal CHEMICAL EQUILIBRIUM has been reached

C HEMICAL EQUILIBRIUM Is reached when the rate of the forward reaction is equal to the rate of the reverse reaction The reaction does not stop The rates are the same but the forward and reverse reactions are still happening Because the rates are the same, the net change in the concentration of A, B, C and D become constant. DYNAMIC EQUILIBRIUM Aa + bB ↔ cC + dD

It is important to remember that at equilibrium the concentrations of chemical species are constant, but not necessarily equal.

L AW OF MASS ACTION General description of equilibrium condition

jA + kB --> nC + mD K = [C] n [D] m [A] j [B] k [A] indicates equilibrium!! K= equilibrium constant

H ABER PROCESS Write law of mass action for forward rxn [NH 3 ] = 3.1 x mol/L [N 2 ] = 8.5 x mol/L [H 2 ] = 3.1 x mol/L

N OW CALCULATE Value of K value of K of reverse rxn K for the following rxn 1/2N 2(g) + 3/2H 2(g) --> NH 3(g)

S OME IMPORTANT INFO If rxn reversed K’ = 1/K Original factor multipled K’’ = K n (# that is mult)

UNITS! Depends on powers of various conc in law of mass action

A PPLICATIONS K values are always the same at specific temps regardless of the amts of reactants that are mixed together initially

R ATIO DEFINED Although K is always the same, the equilibrium conc will not always be the same