1. Kinetics (Reaction Rate)
How Fast Does the Reaction Go

2. Rates of reaction KINETICS
Objectives
To understand that a chemical reaction involves collisions between particles
To be able to describe the four factors which will affect the rate of a chemical reaction.
To describe the factor that can not be changed and affect the rate of a chemical reaction.

3. Collision Theory
In order to react molecules and atoms must COLLIDE with each other.
They must hit each other with enough energy and with the correct orientation.
The more “frequently” the particles hit, the faster the reaction will go.
A COLLISION THAT RESULTS IN PRODUCT IS CALLED EFFECTIVE COLLISION
Anything that increase these effective collisions will make the reaction faster.

4. How do we make the reaction go faster?
There are four things that we can change to make the reaction go faster.
Temperature
Surface area
Concentration
Using a catalyst

5. Temperature
When we increase the temperature we give the particles energy, this makes them move faster, which means they collide with other particles more often.
So the reaction goes faster.

6. Surface area
If we make the pieces of the reactants smaller we increase the number of particles on the surface which can react.
This makes the reaction faster.
The particles on the surface can react
When cut into smaller pieces the particles on the inside can react

7. Concentration There are more particles in the same volume to react
If we make one reactant more concentrated (like making a drink of orange squash more concentrated)
There are more particles in the same volume to react
So the reaction goes faster.
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

8. Factors that Affect Rate
Catalysts- 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.

9. Factors that Affect Rate Summary
Temperature
Higher temperature faster particles.
More and harder collisions.
Faster Reactions.
Concentration
More concentrated means molecules closed together.
Collide more often.
Faster reaction.

10. 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.

11. Using a catalyst
A catalyst is a chemical which is added to a reaction.
It makes the reaction go faster.
The catalyst does not get used up in the reaction.

12. Potential Energy Diagrams
Represent the changes in potential energy that occur during a chemical reaction.
The reaction coordinate represents the progress of the reaction.

13. Remember in terms of energy content
HIGH ENERGY =UNSTABLE
LOW ENERGY = STABLE

14. Classification of reactions
Exothermic Rx: releases energy. Heat part of the products.
Endothermic Rx: absorbs energy. Heat part of the reactants.

15. Definitions
Activation 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.

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

17. Energy
Reactants
Products
Reaction coordinate

18. Activation Energy - Minimum energy to make the reaction happen
Reactants
Products
Reaction coordinate

19. Activated Complex or Transition State
Energy
Reactants
Products
Reaction coordinate

20. Energy
Reactants
Overall energy change (DH)
Products
Reaction coordinate

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

22. What is DH? DH is the enthalpy, or
“heat of reaction.” The amount of energy released or absorbed during a chemical reaction.
By convention
DHrxn = Hproducts - Hreactants

23. What is an exothermic reaction?
A reaction that gives off or releases heat.
Since...
DHrxn = Hproducts - Hreactants
then DHrxn will be a negative number

24. Energy
Reactants
Overall energy change (DH)
Products
Reaction coordinate

25. What is an endothermic reaction?
A reaction that absorbs heat.
Since…
DHrxn = Hproducts – Hreactants
then DH will be a positive number.

26. Products
Energy
Overall energy change (DH)
Reactants
Reaction coordinate

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

28. EXOTHERMIC RX Release heat. DH for reaction is negative
The value for DH is the amount of heat released during the rx
We write the heat it as PRODUCT in the chemical equation
The greater the magnitude of DH the more stable the product will be!!!!

29. Exothermic vs Endothermic

30. ENDOTHERMIC RX Absorb heat DH for reaction is positive
The value for DH is the amount of heat absorbed during the rx
We write the heat it as REACTANT in the chemical equation
The greater the magnitude of DH the more UNstable the product will be!!!!

31. MC Q-FACTORS 2 1 4 3 4 2 1

32. INTERPRETING REACTION COORDINATES handoutB A G F B E I D J C H A

33. HEATS OF REACTION MC 1 4 2 4 1

34. PE DIAGRAMS FOR RX
EXO
-30 20 10 60
ENDO 25 30
SAME H E B G I F A C D