Unit 5: Reaction Kinetics Chemistry Spring 2015. Agenda 4/16/15 Activity: Review Semester 2 Intro: Reaction Kinetics Notes: Kinetics/Catalysis HW: Complete.

Unit 5: Reaction Kinetics

Chemistry Spring 2015

Agenda 4/16/15

• Activity: Review Semester 2

• Intro: Reaction Kinetics

• Notes: Kinetics/Catalysis

• HW: Complete Review Assignment

Reaction Kinetics

What is the definition of kinetics and what is catalysis?

• Kinetics- study of how fast and how reactions occur

• Reaction Rate- how quickly reactants react to form products– Describes how rapidly a chemical change takes

place– Expressing rate depends on a change in some

physical property, like concentration– Measured as a change in # of moles during an

interval of time

Rate = Δ amount of substance used or produced

Δ time Rate = Δ in amount Time Elapsed• Rates can be determined from the disappearance of a

reactant or appearance of a product• As time passes the amount of reactant (squares) and the amount of product

increases (circles)

Reaction:

Catalyst– Catalyst is a substance that

speeds up a reaction without being consumed

– Reactions are able to proceed along a lower energy path

• More reactants have the energy to form products within a given time

• Catalyst lowers Activation Energy (Ea)– Collision posses energy

greater than Ea, collision results in reaction

Agenda 4/20/15

• Go Over PE Diagram Assignment

• Exploding Sugar Article

• Pre-Lab: Factors that affect Rate of Reactions

• HW: Complete Pre-LabTESTS BACK ON TUESDAY

Agenda 4/21

• Go Over Unit 5 Test

• Review the Sugar Explosion Reading

• Lab: Factors Affecting Rate of Reaction

• HW: Finish conclusion for lab

Agenda 4/22

• Complete Kinetics Lab

• Finish Conclusion Questions

• Write Experimental Conclusion

• HW: Lab due tomorrow at beginning of class.

Agenda 4/23

• Kinetics Lab Review – Collect Lab

• Factors Affecting Rates of Reaction Clip

• Notes: Factors• Notes: Reaction Rates

• HW: Complete Reaction Rates Assignment

Concluding Kinetics Lab

• What are the three factors that we measured in this lab?

• How could the rate of reaction be increased? (3 ways)

• How could the rate of reaction be slowed down? (3 ways)

• Collision Theory– Reactions occur when particles collide with one

another with enough Kinetic Energy– When they collide they form the ACTIVATED COMPLEX

What did you observe in lab that affected rate?1. Concentration

– Increase in concentration increases reaction rates

• How does collision theory explain this?– Increasing concentration increases number of collisions

2. Temperature– What happened in lab?– How does collision theory explain this?– Increasing temperature increases KE

» Increases collisions» Higher % of effective collisions

– Increase in temperature increases reaction rates

3. Surface Area– What happened in lab?– Greater surface area, faster reaction rate– Increase in surface area increases the amount of

reactant exposed for a reaction

Examples of rate being affected by surface area, concentration, and temperature.

https://www.youtube.com/watch?v=OttRV5ykP7A

RATE LAW OF CHEMICAL EQUATIONSHow can we determine the value of a reaction rate?

Learning Target #7

Rate Laws

Are “rules” to show what chemicals will affect the rate of reaction

Shows the concentration of substances that affect reaction rate

Looks like: Rate = k [A]n [B]m

18

Rate Laws

Rate = k [A]n [B]m

Rate = change in concentration (M) over change in time (sec)

k = rate constant and depends on temperature

19

Determining Values for Exponents

Rate = k [A]n [B]m

The n and m are called the “order of the reaction” with regard to A and B, respectively.Use experimental dataWe find a chemical’s exponent by changing only

[chemical].

Agenda 4/24

• Warm-up from Notes

• Review Reaction Kinetics Assignment

• Notes: Solving for k units

• HW: Complete Rate Laws PacketQUIZ MONDAY

Solve for k

• The rate constant (k)

• Set up equation for k.

• Plug units in for variables instead of numbers

• Factor out units from equation

Agenda 4/27/15

• Warm-Up– PE Diagrams

• Review Rate Law HW

• Rate Law Quiz

• Notes: Reaction Mechanisms

Kinetics Test on Thursday

Potential Energy. .

Reaction Coordinate

80

70

60

50

40

30

20

10

0

1. What is the energy of the Reactants?2. What is the energy of the Products?3. What is the value of ΔH of this reaction?4. How much energy is needed to initiate this reaction?5. What is the activation energy of this reaction?

Agenda 4/27/15

• Notes: Reaction Mechanisms

• Activity: Reaction Mechanism Practcie

• Review Guide for Kinetics Test

• HW: Kinetics ReviewTest on Kinetics Thursday

Warm-Up

• On a separate sheet of paper:1. Using collision theory, explain why increasing

the concentration of a reactant would increase the rate at which products form. (Draw a picture)

2. Using collision theory, explain why decreasing temperature would slow down the rate of a reaction..

Reaction Mechanisms

How are reaction mechanisms related to the reaction rate?

Reaction Mechanism

• Series of chemical equations (elementary steps) detailing the steps in a chemical reaction.

• These steps add up to create the balanced reaction.

• Intermediate Chemical: A chemical that is present in the mechanism but not present in the balanced equation

2 NO2 + F2 → NO2F + F (slow)

F + NO2 → NO2F (fast)

_____________________________

Balanced Reaction2 NO2 (g) + F2 (g) → 2 NO2F (g)

Rate Determining Step

• Think about getting ready in the morning– What is the rate determining

step?

• Rate Determining Step:– The “slow” step in a chemical

reaction– This step controls how

quickly the reaction proceeds

2 NO2 + F2 → NO2F + F (slow)

F + NO2 → NO2F (fast)

_____________________________

Balanced Reaction2 NO2 (g) + F2 (g) → 2 NO2F (g)