equilibrium in reactions - when forward/reverse reactions occur at same rate  

• ratio of partial pressures, concentrations equals constant
• pressures no longer change
• reaction continues to occur, but ratio stays the same (no net change)
• can be reached from either direction

Haber Process - synthesizing ammonia from hydrogen/nitrogen 

• world’s main source for fixed nitrogen
• N2 + 3H2 <<>> 2NH3

equilibrium constant - only changed by temperature, not by reaction mechanism 

• for reaction aA + bB <<>> cC + dD
• Keq = (C concentration)c(D concentration)d / (A concentration)a(B concentration)b
• value determined by coefficients in chemical equation
• value greater than 1 >> equilibrium towards product side
• value less than 1 >> equilibrium towards reactant side
• for any reaction, constant equal to reciprocal of constant for reverse reaction
• constant raised to power equal to number by which reaction is multiplied
• constants multiplied together for net reactions involving 2+ steps
• do not include pure solids, pure liquids, or solvents in finding constant

For the reaction CaCo3(s) >> CaO(s) + CO2(g), K = 0.0108. Find the equilibrium weight of CO2 if 2g of CaCo3, 2g of CaO, and 0.5g of CO2 were placed in a 1 liter flask.  

• don't take account of solids in the reaction
• K = [CO2] = 0.0108 mol
• 0.0108 mol = grams CO2 / CO2 molar mass
• 0.0108 = grams CO2 / (12 + 16 x 2)
• grams CO2 = 0.0108 (44)
• 0.475 g

At equilibrium for the reaction 2NO(g) + Cl2(g) >> 2NOCl, K = 51. If [NOCl] = 0.10 and [Cl2] = 0.20, find [NO]  

• K = 51 = [NOCl]2 / ([NO]2[Cl2])
• [NO]2 = 0.12 / 0.2 / 51 = 0.00098
• [NO] = 0.031