Equilibrium Most reactions are REVERSIBLE. They go in BOTH direction at the same time.

Equilibrium The forward reaction is left to right. The reverse reaction is right to left.

Equilibrium The reaction is in chemical equilibrium when the forward and reverse reactions are taking place at the same RATE. (*velocity example)

Equilibrium In chemical equilibrium the amounts of the substances are NO LONGER CHANGING. The amounts usually ARE NOT equal to each other. (Similar to dynamic equilibrium in a saturation solution.)

Warm up Equilibrium is dynamic because a. the forward and reverse reactions are still taking place b. the reverse reaction stops but the forward reaction continues c. the forward direction stops but the reverse reaction continues d. the concentrations of reactants and products are constantly changing How do you know if a system has reached equilibrium? a. when the concentrations of products and reactants are equal b. when the rates of the forward and reverse reactions are equal c. when the concentrations of products and reactants are constant d. both b and c

3. Equilibrium is reached closest to what time? a. 2 hoursb. 12 hoursc. 7 hours 4. The color at equilibrium will be more a. Pinkb. colorlessc. blue 5. Which reaction is favored at equilibrium? a. forwardb. reverse 6. What is the INITIAL concentration of reactants? a. 0 mol/Lb mol/Lc mol/Ld mol/L 7. What is the EQUILIBRIUM concentration of reactants? a. 0 mol/Lb mol/Lc mol/Ld mol/L 8. What is the EQUILIBRIUM concentration of products? a. 0 mol/Lb mol/Lc mol/Ld mol/L 9.What is the INITIAL concentration of products? a. 0 mol/Lb mol/Lc mol/Ld mol/L 10. As time increases, the rate of the forward reaction a. increasesb. decreasesc. stays the same blue pink

3. Equilibrium is reached closest to what time? a. 2 hoursb. 12 hoursc. 7 hours 4. The color at equilibrium will be more a. Pinkb. colorlessc. blue 5. Which reaction is favored at equilibrium? a. forwardb. reverse 6. What is the INITIAL concentration of reactants? a. 0 mol/Lb mol/Lc mol/Ld mol/L 7. What is the EQUILIBRIUM concentration of reactants? a. 0 mol/Lb mol/Lc mol/Ld mol/L 8. What is the EQUILIBRIUM concentration of products? a. 0 mol/Lb mol/Lc mol/Ld mol/L 9.What is the INITIAL concentration of products? a. 0 mol/Lb mol/Lc mol/Ld mol/L 10. As time increases, the rate of the forward reaction a. increasesb. decreasesc. stays the same blue pink

K eq K means constant eq means reaction is at equilibrium K eq is the ratio of products to reactants for a given reaction at equilibrium

K eq Math aA + bB cC + dD K eq = [C] c [D] d [A] a [B] b *Only aqueous solutions and gasses are part of K eq. Pure liquids and solids are NOT INCLUDED. *[] = concentrations in M *Small letters are coefficients and become exponents in the K eq equation

K eq = [C] c [D] d [A] a [B] b If K eq > 1 products (forward reaction) are favored at equilibrium If K eq < 1 reactants (reverse reaction) are favored at equilibrium

Le Châtelier ’ s principle N 2 (g) + 3H 2 (g) 2 NH 3 (g) If an equilibrium has been established… … what happens when two NH 3 molecules are removed? You no longer have an equilibrium!

Le Châtelier ’ s principle N 2 (g) + 3H 2 (g) 2 NH 3 (g) The forward reaction is favored so there is more product If an equilibrium has been established… … what happens when two NH 3 molecules are removed? You no longer have an equilibrium!The equilibrium is re-established

Le Châtelier ’ s principle: when a stress (change) is made on a system at equilibrium, the system will shift in a direction that offsets the stress (change). N 2 (g) + 3H 2 (g) 2 NH 3 (g) Favored reaction If removed

3 Stressors Add or remove reactants or products Add or remove heat Change pressure (gasses only)

Concentration and equilibrium Reactants  = shift  Reactants  = shift  Products  = shift  Products  = shift 

Temperature and equilibrium Endothermic (absorbs energy – feels cold) reactions, energy is a reactant Temp  = shift  Temp  = shift 

Temperature and equilibrium Exothermic (releases energy – feels hot) reactions, energy is a product Temp  = shift  Temp  = shift 

Using the equilibrium system predict the direction in which the system will shift as a result of an increase in the concentration of Cl 2. PCl 5 (g) PCl 3 (g) + Cl 2 (g) Concentration and equilibrium

Pressure and equilibrium Pressure only affects gasses Adding pressure stresses the side with MORE MOLES of gas. The equilibrium will shift to the side with fewer moles of gas. Lowering pressure is exactly opposite.

Practice N 2 (g) + 3H 2 (g) 2NH 3 (g) + heat Add N 2 Remove N 2 Add H 2 Remove H 2

Practice N 2 (g) + 3H 2 (g) 2NH 3 (g) + heat Add N 2 Shifts right Remove N 2 Shifts left Add H 2 Shifts right Remove H 2 Shifts left

Practice N 2 (g) + 3H 2 (g) 2NH 3 (g) + heat Raise temperature Lower temperature Raise pressure Lower pressure

Practice N 2 (g) + 3H 2 (g) 2NH 3 (g) + heat Raise temperature Shifts left Lower temperature Shifts right Raise pressure Shifts right Lower pressure Shifts left