1. 7.3 Chemical Kinetics Objectives 3 and 4
Chemistry

2. Essential Questions What is chemical kinetics?
What is a reaction rate?
What is collision theory and how does it relate to rate of reactions?
What is activation energy and how does it relate to rate of reaction?
How do you draw and interpret energy diagrams?
What affects reaction rates and why?

3. Chemical Kinetics Do all reactions occur at the same speed?
No different reactions have different rates
Chemical kinetics focuses on the speed or rate of reactions
A reaction rate is measure of how quickly reactants are converted into products.

4. Reaction Rate (don’t need to write)
18.1
Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.
As time passes, the amount of reactant (red squares) decreases and the amount of product (blue spheres) increases. Rates of chemical reactions are often measured as a change in the number of moles during an interval of time. Interpreting Diagrams Assuming equal time intervals between the boxes, how can you tell that the rate of conversion of reactant to product is not constant throughout this reaction?

5. Collisions Atoms/molecules must collide in order to react
Do all collisions result in a reaction?
No because only some collision successfully lead to formation of products

6. Collision Theory
Collision theory states that atoms, ions, and molecules can react to form products when they collide with both enough kinetic energy and correct orientation
If both conditions are not met there is no reaction
Reaction rate and the number of collisions are proportional

7. Effective Collision (cont)

8. Activation Energy
Activation energy (Ea) is the minimum amount of energy required to react
Ea is the kinetic energy required for the collision to result in a reaction
Reaction rate is inversely proportional to Ea

9. Activated Complex/Transition State
Brief moment where particles are in a transition state
They are not reactants or products, but one big complex

10. Exothermic Energy Diagram
Energy of reactants greater than energy of products
ΔH = Hproducts – Hreactants & Ea = activated - reactants
c is the enthalpy change (∆H) and would be -100 KJ
a is the Ea and would be 50 KJ

11. Endothermic Energy Diagram
Energy of products greater than energy of reactants
c is the enthalpy change (∆H) and would be 200 KJ
a is the Ea and would be 300 KJ

12. Energy Diagram Practice
Label reactants, products, ∆H, Ea
What is the value for Ea and ∆H?
Is the reaction exo or endo?
Ea = 10 KJ; ∆H = -25 KJ
Exo R Ea ∆H P

13. Rate of Reactions What affects the rate of a reaction?
Particle size/surface area
Concentration
Catalyst
Temperature

14. Particle Size
For solids and liquids the more surface area (smaller particle size) the faster the reaction rate
More surface area allows for more collisions to occur which is why the rate increases

15. Concentration
The greater the concentration the greater the reaction rate
Why?
There is more that can react and more collisions

16. Catalyst Catalyst are agents that increase the rate of reaction
Catalyst are not reactants because they are still left at the end of a reaction

17. Catalyst (cont)
Catalyst lowers Ea required to react by providing a different mechanism or path for a reaction to occur that requires less energy

18. Catalyst (cont)
Why does lowering the Ea cause a rxn’s rate to increase?
The lower the Ea the less energy required to react which makes it easier for it react and thus speeds up the reaction

19. Temperature Reaction rate increases and decreases with temperature
If you increase temperature will the reaction go faster or slower? Why?
Faster because the molecules move faster and collide more often leading to more reactions and have more energy when they collide.

20. Essential Questions What is chemical kinetics?
What is a reaction rate?
What is collision theory and how does it relate to rate of reactions?
What is activation energy and how does it relate to rate of reaction?
How do you draw and interpret energy diagrams?
What affects reaction rates and why?

21. 7.3 Tracked Assignment
7.3 Worksheet