Concept #1: Understanding Le Chatelier’s Principle.
According to Le Chatelier’s Principle if a system (chemical reaction) is at equilibrium and we disturb it then the system will readjust to maintain it’s equilibrium state.
Example #1: The following is an endothermic reaction where Kc = 6.73 x 103.
For each of the choices below predict in which direction the reaction will proceed.
Practice: Consider the reaction below:
CH4 (g) + F2 (g) ⇌ CF4 (g) + HF (g) H = + 38.1 KJ/mol
The following changes will shift the equilibrium to the left except one. Which one would not cause a shift to the left?
Practice: The following data was collected for the following reaction at equilibrium
2 A (g) + 3 B (g) ⇌ C (g)
At 25 oC K is 5.2 x 10-4 and at 50 oC K is 1.7 x 10-7. Which of the following statements is true?
a) The reaction is exothermic.
b) The reaction is endothermic.
c) The enthalpy change, ΔH, is equal to zero.
d) Not enough information is given.
When looking at a chemical reaction we look at the two concepts of Kinetics and Thermodynamics to get a total view. However, remember that Le Chatelier’s Principle deals with Thermodynamics and not Kinetics.
Practice: Which direction will the following reaction (in a 10.0 L flask) proceed if a catalyst is added to the system?
CaCO3 (s) ⇌ CaO (s) + CO2 (g) Kp = 3.2 x 10-28
Practice: Consider the following gas reaction of A2 ( shaded spheres) and B2 ( unshaded spheres)
A2 (g) + B2 (g) ⇌ 2 AB (g)
Which container proceeds more to completion?