K c can be used to find a missing [equilibrium] Exam.14.6(p. 625) 0.3 mol CO, 0.1 mol H 2, 0.02 mol H 2 O, plus an unknown amount of CH 4 in 1L. What is the [CH 4 ]? K c = 3.92 CO + 3H 2  CH 4 + H 2 O.

Exer (p 625) 0.02M PCl 3 & Cl 2, plus an unknown amount of PCl 5. K c = What’s [PCl 5 ]? PCl 5(g)  PCl 3(g) + Cl 2(g)

K c ­ can be used to find the [equilibrium] if the [starting] are given. Exam (p 626) Suppose you start with 1 mol of CO & H 2 O in a 50.0 L vessel. How many moles of each substance are in the equilibrium mixture? K c = 0.58 CO + H 2 O  CO 2 + H 2

Exer (p 627). What is the equilibrium composition of the rxn mixture if you start with 0.5 mol of each reactant in a 1.0L vessel. K c =49.7 H 2 + I 2  2HI.

If the [ ] are not perfect squares, then use the quadratic equation. Exam.14.8 p 628 Suppose 1 mol H 2 and 2 mol I 2 are placed in a 1L vessel. How many moles of each substance are present at equilibrium? K c = 49.7 H 2 + I 2  2HI

Exercise (p 629) Initially 1M PCl 5. What is the equilibrium composition? K c = PCl 5(g)  PCl 3(g) + Cl 2(g)

Homework was odds Discuss problems with table

Le Chatelier’s Principle Le Chatelier’s Principle: When a system in chemical equilibrium is disturbed by a change of temperature, pressure or a concentration, the system shifts in equilibrium composition in a way that tends to counteract the change in variable.

Le Chatelier’s Principle The following are three methods of increasing the yield of product. 1. Changing the [ ] by removing products or adding reactants. 2. Changing the partial pressure of gasses by changing the volume. 3. Changing the temperature. Note: catalysts only change the rate at which products are formed, they do not alter the equilibrium composition.

Consider CO + 3H 2  CH 4 + H 2 O, If H 2 O is removed the equilibrium shifts to the right to recreate the H 2 O that was removed. When more reactant is added or some product removed, the equilibrium shifts to the right. When more product is added or some reactant removed, the equilibrium shifts to the left.

Example 14.9 p 631 Predict the shift. H 2 + I 2 2HI; H 2 is removed. CaCO 3(s) CaO (s) + CO 2(g) ; [CO 2 ] is  2Fe + 3H 2 O Fe 2 O 3 + 3H 2 ; [H 2 ] is 

Pressure Effects If the pressure is increased by decreasing the volume, the rxn shifts in the direction of fewer moles of gas.

Example p 634 Predict the shift when the pressure is increased a) CO (g) + Cl 2(g) COCl 2(g) b) 2H 2 S (g) 2H 2(g) + S 2(g) c) C (s) + S 2(g) CS 2(g)

Exercise p 635 Can you increase the amount of product in each of the following rxn by increasing the pressure? Explain a) CO 2(g) + H 2(g) CO (g) +H 2 O (g) b) 4CuO (s) 2Cu 2 O (s) + O 2(g) c) 2SO 2(g) + O 2(g) 2SO 3(g)

Temperature Effects For an endothermic rxn, the amount of products are increased at equilibrium by an increase in temperature. For an exothermic rxn, the amounts of products are increases at equilibrium by a decrease in temperature.

Example p 636 Would a high or low temperature favor the rxn? CO 2 + C 2CO;  H = 172.5kJ

Exercise p 636 Would a high or low temperature favor the conversion of CO 2 to CO by an endothermic rxn?

Exercise p 637 Discuss the temperature and pressure conditions that would give the best yield of carbon monoxide. 2CO 2 2 CO + O 2 ;  H = 566kJ

Homework 63 – 71 odds