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)

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-Lab TESTS 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.

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RATE LAW OF CHEMICAL EQUATIONS How 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 data  We 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 Packet QUIZ 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 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 Review Test 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 NO 2 + F 2 → NO 2 F + F (slow) F + NO 2 → NO 2 F (fast) _____________________________ Balanced Reaction 2 NO 2 (g) + F 2 (g) → 2 NO 2 F (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 NO 2 + F 2 → NO 2 F + F (slow) F + NO 2 → NO 2 F (fast) _____________________________ Balanced Reaction 2 NO 2 (g) + F 2 (g) → 2 NO 2 F (g)