2. Equilibrium: The Story So Far… Condensed Phase Dispersed Phase Pure liquid or solid (l), (s) The rate of particles leaving the system does not depend on the amount Only surface particles are able to leave Solute particles in Solution or Gas (aq), (g) The rate of particles leaving the system does depend on the amount (concentration)

3. Equilibrium: The Story So Far… Saturated solution or Equilibrium vapor pressure Solution can’t hold any more solute or gas can’t hold any more gas particles Particles added to either the condensed or dispersed state will end up in the condensed state.

4. Deriving the Equilibrium Equation Equilibrium K eq Rate reverse  Rate forward We want to eliminate  symbol (need a constant) Rate reverse = (K eq ) Rate forward OR K eq = Rate reverse/Rate forward

5. Deriving the Equilibrium Equation Determining Rate Concentration in the direction of rate Only dispersed phases can change the rate (g or aq) Reverse rate is determined by concentration of product Forward rate is determined by concentration of reactant

6. Deriving the Equilibrium Equation Solving equilibrium problems Write the equilibrium expression for the following: 2H 2 (g) + O 2(g)  2H 2 O (g) Rate Reverse: [H 2 O][H 2 O] Rate Forward: [H 2 ][H 2 ][O 2 ]

7. Deriving the Equilibrium Equation Solving equilibrium problems Write the equilibrium expression for the following: 2H 2 (g) + CO (g)  CH 3 OH (l) Rate Reverse: liquid = 1 Rate Forward: [H 2 ] 2 [CO]