Le Chatelier’s Principle Concentration and Temperature

Day 1: Le Chatelier’s Principle If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Stresses include: Change in concentration Change in volume/pressure Change in temperature

Le Chatelier Change in Concentration PCl5(g) ⇆ PCl3(g) + Cl2(g) ΔH=-47kJ

Warm up #46 Ch.18B left left right right left right Given PCl5(g) PCl3(g)+ Cl2(g) + heat Which way will equilibrium shift given these stresses Remove PCl5 Add heat Increase PCl5 Decrease heat Add Cl2 Remove PCl3 left left right right left right

Day 2: Le Chatelier’s Principle Change in Volume/Pressure Volume and pressure are related. As the volume goes up the pressure goes down and vice versa. (Boyles Law; P1V1=P2V2) Only gases are affected by a change in volume/pressure You need to count the number of moles of gas on each side of the reaction If you add a catalyst, it does not make the reaction favor one direction more than another. All it does is makes the reaction rate increase, which makes the reaction go to equilibrium faster.

2H2O (g) ⇆ 2 H2(g) + O2(g) The left side has 2 molecules of gas, while the right side has 3 molecules of gas If the stress is pressure increasing, shift toward the side with the least number of moles of gas. If the stress is pressure decreasing, shift toward the side with the most number of moles of gas.

Le Chatelier and Pressure - YouTube

Change in Volume/Pressure Stress PCl5(g)  PCl3(g) Cl2(g) heat  pressure    volume  heat catalyst H2(g) I2(g) 2HI(g)  pressure  volume  heat

Practice Stress CO(g) H2 (g)  CH4(g) H2O(g) pressure  volume  heat    volume  heat catalyst N2O4(g) heat 2NO(g)  pressure  volume  heat 2HBr(g) B2(g) H2(g)