Factors Affecting Chemical Equilibrium

1. Factors Affecting Chemical Equilibrium 18.2

2. LeChatelier’s Principle • = If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. • A stress is any kind of change that upsets the equilibrium: • concentration • volume (pressure) • temperature • Catalyst – no effect on equilibrium

3. Concentration changes • CO (g) + 3H2 (g) ↔ CH4 (g) + H2O (g) • If additional CO is put into the system, the concentration of CO is increased which upsets the equilibrium. • The system reacts by making more product (shifts right). • The system could also be made to shift right by removing water.

4. Concentration summary • If you add to one side, the equilibrium shifts to the other side to use up the excess. • If you take away from one side, the system shifts toward that side to make more of what was taken away. • Does NOT change the Keq

5. Volume/pressure changes • CO (g) + 3H2 (g) ↔ CH4 (g) + H2O (g) • Decreasing volume of a gas at a constant temperature will increase the pressure. • Increasing pressure is a stress that the system will relieve by shifting toward the side with fewer moles of gas. • Does NOT change the Keq

6. Temperature changes • Most reactions are exothermic or endothermic. • In an exothermic reaction, heat is a product. • In an endothermic reaction, heat is a reactant. • Increasing temperature is just like increasing concentration, equilibrium shifts away from the increase.

7. Temperature • CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) ∆H =-206.5kJ or CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) + heat Increasing temperature shifts the equilibrium to the left.

8. Temperature • Changing temperature also CHANGES the Keq . • The larger the Keq, the more product is found in the mixture. • So Keq increases in value when temperature is lowered and decreases when the temperature is raised.

9. Temperature Demo • Heat + Co(H2O)6+(aq) + 4Cl-(aq)↔ CoCl42-(aq) + 6 H2O(l) pink blue

10. Biological Equilibrium • Hgb = hemoglobin • Hgb(O2)= oxygenated hemoglobin • Hgb (aq) + O2(g)↔ Hgb(O2) (aq) • Decreased concentration of oxygen and lower pressure at high altitudes shifts equilibrium to left, leaving less Hgb(O2) (aq) to carry oxygen to your muscles.

11. Hgb (aq) + O2(g)↔ Hgb(O2) (aq) • After some time, your body reacts by producing more hemoglobin, which shifts back to the right, increasing the oxygenated hemoglobin.