Kinetics(Reaction Rate)

How Fast Does the Reaction Go

Collision Theory In order to react molecules and atoms

must touch each other.They must hit each other with enough

force and with the correct orientation.The more “frequently” the particles hit,

the faster the reaction will go.Anything that increase these

effective collisions will make the reaction faster.

Factors that Affect RateTemperature

– Higher temperature faster particles.– More and harder collisions.– Faster Reactions.

Concentration– More concentrated closer together the

molecules.– Collide more often.– Faster reaction.

Factors that Affect Rate Particle size

– Molecules can only collide at the surface.– Smaller particles bigger surface area.– Smaller particles faster reaction.– Smallest possible are molecules or ions.

Dissolving speeds up reactions.– Getting two solids to react with each

other is slow.

Factors that Affect RateCatalysts- substances that speed up a

reaction without being used up.(enzyme).– Speeds up reaction by giving the

reaction a new path.– The new path has a lower activation

energy.– More molecules have this energy.– The reaction goes faster.

Inhibitor- a substance that blocks a catalyst.

Potential Energy Diagrams

Represent the changes in potential energy that occur during a chemical reaction.

The reaction coordinate represents the progress of the reaction.

Remember in terms of energy content

HIGH ENERGY =UNSTABLELOW ENERGY = STABLE

Classification of reactions

Exothermic Rx: releases energy. Heat part of the products.

Endothermic Rx: absorbs energy. Heat part of the reactants.

DefinitionsActivation Energy: the minimum amount

of energy needed to start up a chemical reaction.

 Activated Complex: a temporary

intermediate product. Highest point of the diagram. Is UNSTABLE.

 

Catalyzed Reactions

Need less energy to start up the reaction. The presence of a catalyst LOWERS THE ACTIVATION ENERGY!!!

Ene

rgy

Reaction coordinate

Reactants

Products

Ene

rgy

Reaction coordinate

Reactants

Products

Activation Energy - Minimum energy to make the reaction happen

Ene

rgy

Reaction coordinate

Reactants

Products

Activated Complex or Transition State

Ene

rgy

Reaction coordinate

Reactants

Products

Overall energy change (H)

Thermochemistry

The study of the changes in heat energy that accompany chemical reactions and physical changes.

What is H?

H is the enthalpy, or

“heat of reaction.” The amount of energy released or absorbed during a chemical reaction.

By convention

Hrxn = Hproducts - Hreactants

What is an exothermic reaction?

A reaction that gives off or releases heat.

Since...

Hrxn = Hproducts - Hreactants

then Hrxn will be a negative number

Ene

rgy

Reaction coordinate

Reactants

Products

Overall energy change (H)

What is an endothermic reaction?

A reaction that absorbs heat.

Since…

Hrxn = Hproducts – Hreactants

then H will be a positive number.

Energy

Reaction coordinate

Reactants

Products

Overall energy change (H)

Heats of Reaction Table IThe new reference table (Table I) shows different heats of reaction for some common reactions.

EXOTHERMIC RXRelease heat.H for reaction is negativeThe value for H is the amount of heat

released during the rxWe write the heat it as PRODUCT in the

chemical equationThe greater the magnitude of H the

more stable the product will be!!!!

Absorb heatH for reaction is positiveThe value for H is the amount of heat

absorbed during the rxWe write the heat it as REACTANT in the

chemical equationThe greater the magnitude of H the

more UNstable the product will be!!!!

ENDOTHERMIC RX

PAGE 140 ANSWERS RB 2012 edition11. 4

12. 2

13. 1

14. 2

15. 2

16. 1

17. 3

INTERPRETING REACTION COORDINATES handout

1) B

2) A

3) G

4) G

5) A

6) F

7) F

8) F

9) F

10) B

11) E

12) I

13) D

14) J

15) C

16) H

17) H

18) A

PE DIAGRAMS FOR RX 1. EXO

2. -30

3. 20

4. 10

5. 60

6. ENDO

7. 25

8. 20

9. 30

10. SAME

11. H

12. E

13. B

14. G

15. I

16. F

17. A

18. C

19. D

HEATS OF REACTION MC1) 1

2) 1

3) 4

4) 2

5) 2

6) 2

7) 2

8) 1

9) 1

10) 4

11) 4

12) 1