i. rates of reaction ch. 16 – reaction energy and reaction kinetics

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I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

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Page 1: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

I. Rates of ReactionCh. 16 – Reaction Energy and

Reaction Kinetics

Page 2: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

A. Collision Theory

• Reaction rate depends on the collisions between reacting particles

• The particles collide and make new substances

• Successful collisions occur if the particles...– collide with each other

– have the correct orientation

– have enough kinetic energy to break bonds

Page 3: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

A. Collision Theory

Particle Orientation

Required Orientation

Successful Collision Unsuccessful Collisions

Page 4: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

B. Activation EnergyActivation Energy (Ea)

– minimum energy required for a reaction to occur

– Activated Complex: the transitional structure in a collision that exists while old bonds are breaking and new bonds are being formed

ActivationEnergy

Page 5: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

B. Activation Energy

Activation Energy:- depends on reactants- is always positive

- low Ea = fast reaction rate

- takes less energy for the reaction to start

Ea

Page 6: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

C. Factors Affecting Rxn Rate1. Nature of Reactants

- the rate of reaction depends on the particular reactants and the bonds involved

2. Surface Area– high SA = fast rxn rate– more opportunities for collisions– Increase surface area by…

• using smaller particles – increase locations of collisions

• dissolving in water – particles can mix & collide freely so reactions happen rapidly

Page 7: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

C. Factors Affecting Rxn Rate

3. Concentration

- high conc = fast rxn rate

- more opportunities for collisions because there are more particles in the same volume that can react

There are less red particles in the same volume so there is less chance of a collision

There are more red particles in the same volume so there is more chance of a collision so the reaction goes faster

Page 8: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

C. Factors Affecting Rxn Rate4. Temperature

- high temp = fast rxn rate- high KE

- ↑ temperature, ↑ energy- particles move faster- more opportunities for

collision- easier to reach activation

energy

Page 9: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

C. Factors Affecting Rxn Rate5. Catalyst

– substance that increases rxn rate without being consumed in the rxn

– lowers the activation energy

Page 10: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

II. Energy DiagramsCh. 16 – Reaction Energy and

Reaction Kinetics

Page 11: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

A. Terms and Symbols

• Reactants: chemicals to start in a reaction• Products: chemicals formed during

reaction

• Heat of reaction (Hrxn): difference in energy between reactants and products (units are Joules)

• Activation Energy (Ea): amount of energy required for the reaction to take place. The higher the Ea, the slower the reaction (units are Joules)

Page 12: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

B. Energy Diagrams• Show relationship between time and energy during the course of a chemical reaction

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Reactants

H

Products

Forward Rxn

(exothermic)

Reverse Rxn

(endothermic)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Ea

Course of Reaction (time)

En

erg

y (E

) in

kJ/

mo

l

Page 13: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

C. Endothermic Reaction

• Products have higher enthalpy than reactants• The pink curve is the uncatalyzed reaction• The blue curve shows what happens when a catalyst is

present– Energies and amounts of the products and reactants stays

the same, and the rxn stays the same – catalyst just allows reaction to reach equilibrium faster

Course of Reaction

Ene

rgy

• A reaction in which heat is absorbed

Page 14: I. Rates of Reaction Ch. 16 – Reaction Energy and Reaction Kinetics

D. Exothermic Reactions

• Reactions in which heat is released

• Products have lower enthalpy than reactants• The blue curve shows uncatalyzed reaction, red curve

shows what happens when a catalyst is present• Only change is the amount of time for the reaction to

reach equilibrium• Referred to as “spontaneous” because they can proceed

to products without outside intervention

Course of Reaction

Ene

rgy