Equilibrium Chapter 18

Collision Theory a reaction is more likely to occur if reactant particles collide with proper energy and orientation Reaction Rate How fast the reaction proceeds Activation Energy (EA) Minimum energy that colliding particles must have in order to react

Proper Orientation

Reversible Reactions Reversible Reaction Reaction in which conversion of reactants to products and conversion of products to reactants occurs simultaneously

Equilibrium Rate of forward reaction is equal to rate of reverse reaction The rate at which products are formed is equal to the rate at which products are converted back to reactants

Equilibrium There is no net change in the actual amounts of the reactants and products. Amounts (concentration) remain constant Dynamic Equilibrium Reactions are still happening Reaction rate does not equal 0

Equilibrium Saturated Solution Solid in equilibrium with dissolved particles

Equilibrium Constants Temperature dependent

LeChatelier’s Principle If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress

Stresses Against Dynamic Equilibrium Change in concentration of reactant or product Change in temperature Change in pressure Only applies to reactions in the gas phase with unequal number of moles of gas.

Example How does adding more carbon dioxide shift equilibrium? Equilibrium will shift towards reactants

What does “Shifting” mean? Adding more products will cause more reverse reaction to occur Rate of reverse reaction increases More products are converted into reactants Amounts of products decrease, reactants increase Shift towards Reactants

Example How will increasing the temperature affect equilibrium? Equilibrium will shift towards the reactants

Example How will increasing pressure affect equilibrium? Equilibrium will shift towards the products Increasing pressure always shifts equilibrium towards the side with the least number of moles of gas.

Common Ion Effect How will adding potassium chloride affect equilibrium? Equilibrium will shift towards the reactants

Review When a bond is formed energy is released Bonded atoms are more stable together than free atoms Energy must be added or absorbed in order to break a bond It takes energy to pull atoms apart, since they are more stable together

Review Endothermic Exothermic Energy being added N2 + O2 + 182.6kJ  2NO Exothermic Energy being released 2CO + O2  2CO2 + 566kJ

Potential Energy Potential Energy (PE) Heat of Reaction (ΔH) Energy stored in chemical bonds Heat of Reaction (ΔH) Energy absorbed or released during a chemical reaction PEProducts – PEReactants

Potential Energy Diagram Graphically shows energy released or absorbed during a reaction Reaction Process Energy Energy Reaction Process

Potential Energy Diagram On a Potential Energy Diagram, you must be able to identify the following: Potential Energy of Reactants, PEReactants Potential Energy of Products, PEProducts Heat of Reaction, ΔH Activation Energy, EA

Exothermic Reaction EA Energy PEReactants ΔH PEProducts Reaction Process Energy EA PEReactants ΔH PEProducts

Endothermic Reaction EA Energy PEProducts ΔH PEReactants Reaction Process ΔH PEProducts PEReactants

Table I Shows reactions with ΔH Endothermic Exothermic ΔH =PEProducts – PEReactants Endothermic ΔH = (+) Exothermic ΔH = (-)

Factors Affecting Reaction Rates Temperature Concentration Surface Area Catalyst

Factors Affecting Reaction Rates Temperature Increasing temperature increases the reaction rate Concentration increasing the number of particles in a given volume (concentration) increases the reaction rate

Factors Affecting Reaction Rates Surface Area increasing surface area increases reaction rate Catalyst the presence of a catalyst will often increase reaction rate Catalysts are not used up during a reaction

Affect of a Catalyst Provides an alternate pathway for the reaction to proceed Decreases activation energy Increases reaction rate

Affect of a Catalyst Energy Reaction Process Without Catalyst With Catalyst

Entropy Measure of randomness or disorder Systems in nature tend to undergo changes towards lower energy and higher entropy The universe is lazy and disorganized

Entropy Increasing Entropy Solid < Liquid < Gas Solid < Dissolved