1. Reaction quotient, Q
In an equilibrium system, all substances must be present.
When only “reactants” are provided, the system is clearly not at equilibrium. The forward reaction will occur at a faster rate than the reverse reaction until the system achieves equilibrium.
When only “products” are provided, the system is clearly not at equilibrium. The reverse reaction will occur at a faster rate than the forward reaction until the system achieves equilibrium.

2. Reaction quotient, Q
But, what if all of the components are present initially? How will I determine
a) if the system is at equilibrium, and
b) if it isn’t, which reaction will happen more to reach equilibrium?
To do this, you will solve for the reaction quotient, Q.

3. Reaction quotient, Q Q has the exact same formula as K.
Q is the ratio of products to reactants at any point during the reaction.
K is the ratio of products to reactants specifically at equilibrium.
(SEE DIAGRAM ON BOARD)

4. Reaction quotient, Q If Q = K, the system is at equilibrium.
If Q is less than K, the system needs to shift right to reach equilibrium.
If Q is greater than K, the system needs to shift left to reach equilibrium.

5. Consider the equilibrium: 2 SO2(g) + O2(g) ↔ 2 SO3(g) Kc = 4.36
For the following initial values, find Q and determine which direction the system will shift to reach equilibrium.
[SO2] = 1.10 M, [O2] = .836 M, and [SO3] = 2.10 M
[SO2] = 2.00 M, [O2] = 1.50 M, and [SO3] = 1.25 M
[SO2] = .980 M, [O2] = 1.42 M, and [SO3] = 4.25 M

6. SO2(g) + NO2(g) SO3(g) + NO(g)
At a certain temperature, Kc = The initial concentrations for both SO2 and NO2 are M. For SO3 and NO, the initial concentrations are M. Determine the concentrations of all substances at equilibrium.