Chemistry Topic 8

Kinetics and Equilibrium

• 2/23 Chemistry

• Kinetics and Equilibrium

• Aim: How do different factors affect reaction rates?

• Obj: SWBAT analyze trends in reactions and understand the underlying mechanisms behind them

• Do Now: How do you think reactions occur?

• Collision Theory – in order for a reaction to occur, reactant particles must collide

• Collisions can produce a reaction if BOTH THE SPATIAL ORIENTATION AND ENERGY of colliding particles are sufficient

Factors that Affect Rate of Reaction

Factor Increases Rate

Nature of Reactants Ionic more than covalent

Concentration Increased concentration

Pressure Increased pressure for gases

Temperature Increased temperature

Surface Area Increased surface area

Catalyst Presence of catalyst

Potential Energy Diagrams

• MUST MEMORIZE NEXT SLIDE

• X-axis = reaction coordinate progress of reaction

• Y-axis = potential energy

• Activated complex = temporary product that can either break apart or form products

F

• A = Potential Energy of the Reactants

• B = Activation Energy of the Forward Reaction

• C = Activation Energy of the Reverse Reaction

• D = Heat of the Reaction (∆H)

• E = Potential Energy of the Products

• F = Potential Energy of the Activated Complex

Endo vs Exo

Endo vs. Exo

• Endothermic

– ∆H is Positive

• Exothermic

– ∆H is Negative

• ∆H = (PE products – PE reactants)

Catalyst

• Catalyst = substance that increases the rate of a reaction by

– Providing a different and easier pathway for the reaction

–LOWER THE ACTIVATION ENERGY!!!

• 2/24 Chemistry

• Kinetics and Equilibrium

• Aim: What is equilibrium and how is it maintained?

• Obj: SWBAT describe different forms of equilibrium and how different stresses affect it.

• Equilibrium – When both the forward and reverse reactions occur at the same rate

– Use a double arrow to show this ()

– MUST BE IN A CLOSED SYSTEM OR CONTAINER

Types of Equilibrium

• Phase equilibrium

– Ex. H20(s) H2O(l)

• Solution equilibrium

– Occurs in saturated solutions as quickly as something is dissolving, it is also falling out of solution

• Chemical equilibrium

Le Châtelier’s Principle

• Stress = any change in temperature, concentration, or pressure on an equilibrium system

Le Châtelier’s Principle

Concentration changes

• Increase concentration

– Shift equilibrium away from the increase, increase everything the arrow is pointing to and decrease whatever’s left

• Decrease concentration

– Shift equilibrium to the decrease, increase everything the arrow is pointing to and decrease whatever’s left

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) + heat

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) + heat

Temperature Changes

• Increase Temperature

– Shift away from heat, increase everything the arrow is pointing to and decrease whatever’s left

• Decrease Temperature

– Shift towards heat, increase everything the arrow is pointing to and decrease whatever’s left

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) + heat

N2(g) + O2(g) + heat 2NO(g)

Pressure Change

• ONLY AFFECTS GASES!!!

• Increase Pressure – Shift toward side with fewer moles of gas, increase

everything the arrow is pointing to and decrease whatever’s left

• Decrease Pressure – Shift toward side with more moles of gas, increase

everything the arrow is pointing to and decrease whatever’s left

• IF MOLES OF GAS ARE EQUAL NO EFFECT!!!

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

N2(g) + O2(g) 2NO(g)

NO EFFECT

P

Effect of Catalyst

• Catalyst changes both forward and reverse reactions equally

• 2/26 Chemistry

• Kinetics and Equilibrium

• Aim: What are enthalpy and entropy and how do they affect reactions?

• Obj: SWBAT explain the concepts of enthalpy and entropy

• HW: Finish worksheets

Enthalpy

• The tendency in nature to change to a state of lower energy.

• Exothermic reactions do this naturally because products have less energy than reactants.

Entropy

• Randomness or disorder

• There’s a tendency in nature to go towards greater randomness or disorder

• Gas has more entropy than liquids which have more entropy than solids

• More moles = more entropy

• Practice

• 2/29 Chemistry

• Kinetics and Equilibrium

• Aim: How do we review the information present in this chapter?

• Obj: SWBAT explain the concepts of kinetics and equilibrium

• HW: Study for test tomorrow

• Do Now: Fill out Zip Grade with answers to multiple choice of the review packet.

• 3/1 Chemistry

• Kinetics and Equilibrium

• Aim: How do we review the information present in this chapter?

• Obj: SWBAT explain the concepts of kinetics and equilibrium

• HW: Study for test tomorrow

• Do Now: Begin Review Packets

• 3/4 Chemistry

• Kinetics and Equilibrium

• Aim: How do we construct PE diagrams based on data?

• Obj: SWBAT follow procedures and construct PE graphs

• Do Now: Grab Lab Folders