7. Equilibrium

• when all reactants and products are in one phase, the equilibrium is homogenous • if one or more reactants or products are in a different phase, the equilibrium is heterogenous

For an equilibrium reaction of the form aA + bB <—> cC + dD At constant temp: [C]c•[D]d / [A]a•[B]b = Kc • if Kc is very large, reaction goes to completion • if Kc is very small, the reaction would be considered to not occur

Temperature • the only thing that can change the value of Kc • high temp moves equilibrium endothermic reaction right, exothermic reaction left Concentration • increased conc shifts equilibrium to the opposite side Pressure • increased pressure shifts to the side with the least moles

N2(g) + 3H2(g) <—> 2NH3(g) dH = -92kJ/mol 200 atm | 450 c | iron catalyst • Equilibrium theory favors low temp, high pressure • Kinetic theory favors high temp, pressure and catalyst • conditions are a compromise with the catalyst so the reaction can happen at a lower temp

• Fertilizers • Nitric Acid • ammonia can be oxidised to nitric acid –> nitric acid can make fertilizers, explosives polyamide polymers

aA + bB <—> cC + dD Q = Cc x Dd / Aa x Bb • used to determine if a reaction will occur • used to determine if a salt will dissolve Q > K products are great/ reverse reaction favored Q = K both reactions occuring in equilibrium Q < K reactants are great/ forward reaction favored

For an insoluble salt: MX(s) <—> M+(aq) + X-(aq) The Keq will not change significantly Ksp = [M][X]

K = 1 Equilibrium dG = 0 K > 1 products favored dG < 1 K < 1 reactants favored dG > 1