1. Equilibrium
Chapter 18

2. 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

3. Proper Orientation

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

5. 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

6. 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

7. Equilibrium Saturated Solution
Solid in equilibrium with dissolved particles

9. Equilibrium Constants
Temperature dependent

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

11. 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.

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

13. 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

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

15. 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.

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

18. 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

19. Review Endothermic Exothermic Energy being added
N2 + O kJ  2NO
Exothermic
Energy being released
2CO + O2  2CO kJ

20. 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

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

22. 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

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

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

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

27. Factors Affecting Reaction Rates
Temperature
Concentration
Surface Area
Catalyst

28. 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

29. 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

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

31. Affect of a Catalyst Energy Reaction Process Without Catalyst
With Catalyst

32. 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

33. Entropy Increasing Entropy Solid < Liquid < Gas
Solid < Dissolved