1. Equilibrium Constant

2. Example H2 + F2 2HF The equilibrium constant for the reaction above is found to be 2.1 x 103 at a specific temperature. At equilibrium, the concentrations of both hydrogen and fluorine are found to be 0.0045 M. What is the equilibrium concentration of hydrogen fluoride?

3. Example • A mixture of 5.00 x 10-3 mole of H2 and 1.00 x 10-2 mole of I2 is placed in a 5.00L container and allowed to come to equilibrium. Analysis of the equilibrium mixture shows the concentration of HI is 1.87 x 10-3 M. Calculate the Kc at 448°C for this reaction. H2 + I2 2HI

4. Example • Sulfur trioxide decomposes at high temperatures in a sealed container as shown: 2SO3 2SO2 + O2 Initially the vessel is charged at 1000K with 6.09 x 10-3 M SO3. At equilibrium the SO3 concentration is 2.44 x 10-3 M. Calculate the Kc at 1000K.

5. Kc and Kp • When concentration is expressed in M use Kc as the constant. • When concentration is expressed in atm use Kp • aA  cC + dD • Kp = Pcc PDd / PAa

6. Example • The reaction for the formation of nitrosyl chloride 2NO(g) + Cl2(g)  2NOCl(g) was studied at 25°C. The pressures at equilibrium were found to be PNOCl= 1.2atm, PNO = 5.0x10-2atm, and PCl = .3atm. Calculate the Kp for this reaction.

7. Kp from Kc • Kp = Kc (RT)n • n – total coefficients of gaseous products minus total coefficients of gaseous reactants • R = .0821 L atm/mol K

8. Example • The Kc for the reaction N2 + 3H2 2NH3 is .105. Calculate the Kp at 472°C.

9. Solids and Liquids • The concentrations of pure solids and liquids in a reaction does not really change • They are not included in the equilibrium expression

10. Example • Write the equilibrium expression for: CO2(g) + H2(g)  CO(g) + H2O(l) SnO2(s) + 2CO(g)  Sn(s) + 2CO2(g)