1. 9.2 Equilibrium Constant and Reaction Quotient Obj S1:e-g
Chemistry

2. Essential Questions
What is the equilibrium constant and how do you calculate it?
What does the equilibrium constant tell you about the concentration and reaction rate?
What is the reaction quotient and how do you calculate it?
How do you use the reaction quotient to determine if a reaction is at equilibrium?

3. The Equilibrium Constant
The equilibrium constant (Keq) is a ratio of products to reactants at equilibrium.
aA +bB ↔cC +dD
Lower case letter represent coefficients
Upper case letters represent compounds
[ ] are Concentrations of a given substance
Pure solids and liquids are written as values of 1 in the expression

4. Values of K K < 1 K ≈ 1 If K > 1
Reactants and products have about the same concentration
If K > 1
More products than reactants or equilibrium lies to the right, forward reaction is favored
K < 1
More reactants than products or equilibrium lies to the left, reverse reaction is favored
The only external factor which changes Keq is the temperature.

5. Calculating Keq
Determine the Keq for the following reaction

6. Calculating Keq (cont)
An equilibrium mixture of N2, O2 , and NO gases at
1500 K is determined to consist of 6.4  10–3 mol/L of
N2, 1.7  10–3 mol/L of O2, and 1.1  10–5 mol/L of NO.
What is the equilibrium constant for the system at
this temperature? Would there be more products or reactants

7. Calculating Keq (cont)
Calculate Keq for 5.6 M NaHCO3, 3.4 M Na2CO3, 5.1 H2O and 7.7 M CO2. Are the products or reactants favored? Which reaction is favored the forward or reverse?
2 NaHCO3 (s) ↔ Na2CO3 (s) + H2O (g) + CO2 (g)

8. Reaction Quotient
Reaction quotient (Q) is used to find out if a reaction is at equilibrium
The reaction quotient is the same as the equilibrium constant except the concentrations are from when the measurement was taken and not at equilibrium

9. Reaction Quotient (cont)
If Q < Keq then the reaction needs to proceed (shift) to the right to reach equilibrium
If Q > Keq then the reaction will proceed to the left
If Q = Keq then the reaction is at equilibrium

10. Reaction Quotient (cont)
The following reaction has Keq = There are 0.65 atm PCl3, 0.40 atm Cl2, and 0.20 atm PCl5. What is the Q value and what direction will the reaction shift to achieve equilibrium?
PCl3 (g) + Cl2 (g) ↔ PCl5 (g)

11. Essential Questions
What is the equilibrium constant and how do you calculate it?
What does the equilibrium constant tell you about the concentration and reaction rate?
What is the reaction quotient and how do you calculate it?
How do you use the reaction quotient to determine if a reaction is at equilibrium?

12. 9.2 Tracked Assignment
Worksheet