Percent Reaction and Q

1
Percent Reaction and Q

• Chem 12
• Page 509 517-520

2
Percent Reaction

• The yield of product measured at equilibrium
  compared with the maximum possible yield of
  products.
• Example H2 I2 lt -- gt 2HI
• HI at equilibrium 1.56M
• HI quantitative in forward reaction 2.00M
• rxn HIeq/ HIfrxn x 100
• 1.56M/2.00M x 100 78

3
Need to Know

• lt 50 reactants favored small K
• gt 50 products favored large K
• gt 99 Quantitative Forward reaction ? Totally
  a forward reaction, no equilibrium

4
Reaction Quotient, Qc

• Identical expression to Kc, but its value is
  calculated using concentrations that arent
  necessarily found at equilibrium.
• If Qcgt Kc shifts to reactants
• If Qclt Kc shifts to products
• If Qc Kc equilibrium

5
Practice Problem

• Calculate the Q for the following reaction using
  these equilibrium concentrations N2 0.10 M
  H2 0.30 M and NH3 0.20 M. Is the system
  at equilibrium if Kc of the reaction is 0.40?
• N2 3H2 lt -- gt2NH3
• Answer Not at equilbrium, QgtK, so shift to left
  (reactants)