Unit 5: Reaction Kinetics Chemistry Spring 2015
Dec 29, 2015
Agenda 4/16/15
• Activity: Review Semester 2
• Intro: Reaction Kinetics
• Notes: Kinetics/Catalysis
• HW: Complete Review Assignment
• 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
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 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)