AP Chemistry - Semester 2: Equilibrium: the extent of Chemical Reactions

Sections: Introduction   |  Section 1   |  Section 2   |  Section 3   |  Section 4   |  Section 5   |   Lab

17.5 How to Solve Equilibrium Problems If you are given equilibrium quantities as concentrations of partial pressures you can solve for K by substituting the values into the reaction quotient. Example: N2(g) + 3H2(g) > 2NH3(g) The equilibrium concentrations for: N2= 0.15 mol/L H2= 0.80 mol/L NH3 = 0.20 mol/L If some of the equilibrium quantities are not given, use a reaction table to show initial quantities, the changes in these quantities during reaction and the equilibrium quantities to solve for the unknown. Using the same equation as the last example: N2(g) + 3H2(g) > 2NH3(g) If we start with: N2= 0.18 mol/L H2= 0.18 mol/L The equilibrium concentration of ammonia is 0.040 mol/L. Calculate Kc   N2 3H2 2NH3 Initial [] 0.18 0.18 0 change -x -3x +2x Equilibrium [] 0.18-x 0.18-3x 0+2x If the equilibrium concentration of NH3 = 0.040mol/L then 2x = 0.040 x = 0.020 [N2] = 0.18-x = 0.18-0.020= 0.16 [H2] = 0.18-3x = 0.18-o.060 – 0.12 Next page

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