Equilibrium

1. Equilibrium • A + B  C – This is a reaction that goes to completion(no A and B remains, all of it turns into C) and only goes 1 way (left to right) • A + B  C – This is a reaction that does not go to completion (A, B, and C remain), it goes forward (left to right) and reverse (right to left), that is it is a reversible reaction where A and B turn into C at the same rate that C turns into A and B.

2. Equilibrium Constant • Relates the concentrations of reactants to the concentrations of products • Equiliburm Constant – Kc – “c” stands for concentrations (molarity) aA + bB cC • Kc= [products]coefficients = [C]c____ [reactants]coefficients[A]a[B]b

3. Stuff about K • Include gases and aqueous solutions only • If all of the substances are gases, calculate Kp instead of Kc; relationship between Kp and Kc,Kp = Kc(RT)n • K is a function of temperature, even though it’s not shown in the equation • Only use equilibirum concentrations (NOT initial) • Kc reverse = 1/Kc forward (they are inverses of each other) • If you multiply the equation by a whole #, you raise K to that power • If a reaction occurs in a series of steps where you add the reactions to get the overall equation, multiply the individual K’s to get the overall K

4. Practice At a given temperature, K = 1.3 X 10-2 for the reaction N2(g) + 3H2(g)  2NH3(g). Calculate K for the following reactions at this temperature. a. ½ N2(g) + 3/2H2(g)  NH3(g) b. 2NH3(g)  N2(g) + 3H2(g) c. NH3(g)  1/2 N2(g) + 3/2H2(g) d. 2N2(g) + 6H2(g)  4NH3(g)

5. Q – reaction quotient • Use to determine if you are at equilibrium or not • Calculate the same way you calculate K • Q = K – at equilibrium • Q < K – forward reaction needs to “go” • Q > K – reverse reaction needs to “go”

6. Percent ionization % = equilibrium concentration Initial concentration *100