1. 7.4 Predicting the Direction of a Reaction
Reading: Pages
Practice: Pg. 356 #26-28

2. The Reaction Quotient (Q)
To calculate Q, one substitutes the initial concentrations on reactants and products into the equilibrium expression.
Q gives the same ratio the equilibrium expression gives, but for a system that is not at equilibrium. 2

3. the system is at equilibrium.
If Q = K,
the system is at equilibrium. 3

4. there is too much product and the equilibrium shifts to the left.
If Q > K,
there is too much product and the equilibrium shifts to the left. 4

5. there is too much reactant, and the equilibrium shifts to the right.
If Q < K,
there is too much reactant, and the equilibrium shifts to the right. 5

6. Le Châtelier’s Principle
Reading: Pages
Practice: Pg. 366 #29-33
Section Review: Pg. 370 #1-5
Handouts/Worksheets

8. Le Châtelier’s Principle
“If a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.”
Systems shift from “Q” towards “K”.

9. Le Châtelier’s Principle
System starts at equilibrium.
A change/stress is then made to system at equilibrium.
Change in concentration
Change in volume/Change in pressure
Change in Temperature
System responds by shifting to reactant or product side to restore equilibrium.

10. Le Chatlier’s Principle (cont)

11. Le Chatlier’s Principle (cont)

12. Le Châtelier’s Principle; Temperature Effect