Chapter 18: Chemical Equilibrium Table of Contents Chapter 18: Chemical Equilibrium 18.2: Factors affecting chemical equilibrium

Factors Affecting Chemical Equilibrium Chemical Equilibrium: Basic Concepts Factors Affecting Chemical Equilibrium Le Châtelier’s principle: If a system at equilibrium is stressed, it will shift to reduce the stress. Rule of Thumb: “Same side does the opposite, opposite side does the same” Equilibrium shifts in the direction that increases after the change.

Factors Affecting Chemical Equilibrium Chemical Equilibrium: Basic Concepts Factors Affecting Chemical Equilibrium Equilibrium can be disturbed by 3 factors: 1. Changing concentration: adding or removing a reactant or product. 2. Changing temperature 3. Changing volume & pressure

Factors Affecting Chemical Equilibrium Chemical Equilibrium: Basic Concepts Factors Affecting Chemical Equilibrium 1. Changing Concentration: Removing a Reactant or a Product Adding a reactant makes it form more products , causes the equilibrium to shift to the right Adding the product makes it form more reactant, causes a shift to the left

Factors Affecting Chemical Equilibrium Chemical Equilibrium: Basic Concepts Factors Affecting Chemical Equilibrium 1. Removing a Reactant or a Product Removing/diluting a reactant makes it form more reactants, causes the equilibrium to shift to the left Removing/diluting the product makes it form more product, causes a shift to the right

Practice adding and removing: How will it effect equilibrium if you… Add NO? shifts to the right, forms more products Add Br2? shifts to the right, forms more products Add NOBr? shifts to the left, forms more reactants Remove NOBr? shifts to the right, forms more products Remove Br2? shifts to the left, forms more reactants Remove NO? shifts to the left, forms more reactants

2. Changes in temperature Chemical Equilibrium: Basic Concepts 2. Changes in temperature Changes in temperature, causes a shift in equilibrium by changing the value of Keq. In contrast, changes in concentration or pressure cause a shift in equilibrium without changing Keq

2. Changes in temperature Chemical Equilibrium: Basic Concepts 2. Changes in temperature Treat heat as any other reactant or product Exothermic = heat is a product Reactants ↔ Products + heat Endothermic = heat is a reactant Reactants + heat ↔ Products

2. Changes in temperature Chemical Equilibrium: Basic Concepts 2. Changes in temperature Increase in temp shift to left, Keq decreases Decrease in temp shift to right, Keq increases

Practice changes in temp: heat + 6CO2(g) + H2O(l) = C6H12O6(aq) + 6O2(g) How will it effect equilibrium if you… Increase temperature shift to the right, Keq increases Decrease temperature shift to the left, Keq decreases

3. Changes in volume & pressure Chemical Equilibrium: Basic Concepts 3. Changes in volume & pressure In a gaseous system, volume and pressure are interconnected. ↓ volume, ↑ pressure ↑ volume, ↓ pressure Shift to side with fewest moles Shift to side with most moles

3. Changes in volume & pressure Chemical Equilibrium: Basic Concepts 3. Changes in volume & pressure How will this reaction respond to the following changes: Increase in pressure shift to right Increase in volume shift to left

Practice changes in vol & press: How would increasing the volume of the reaction vessel impact each of these equilibria? shift to the left shift to the right

Practice changes in vol & press: How would increasing the pressure of the reaction vessel impact each of these equilibria? shift to the right shift to the left

3. Changes in volume & pressure Chemical Equilibrium: Basic Concepts 3. Changes in volume & pressure When molesreactants = molesproducts volume and pressure have no effect on equilibrium.