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

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Presentation on theme: "Kinetics (Reaction Rate) How Fast Does the Reaction Go."— Presentation transcript:

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2 Kinetics (Reaction Rate) How Fast Does the Reaction Go

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

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

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

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

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

8 Concentration l If we make one reactant more concentrated (like making a drink of orange squash more concentrated ) l There are more particles in the same volume to react l 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

9 Factors that Affect Rate l 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. l Inhibitor- a substance that blocks a catalyst.

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

11 l Particle size – Molecules can only collide at the surface. – Smaller particles bigger surface area. – Smaller particles faster reaction. – Smallest possible are molecules or ions. l Dissolving speeds up reactions. – Getting two solids to react with each other is slow.

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

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

14 Remember in terms of energy content l HIGH ENERGY =UNSTABLE l LOW ENERGY = STABLE

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

16 Definitions l Activation Energy: the minimum amount of energy needed to start up a chemical reaction. l Activated Complex: a temporary intermediate product. Highest point of the diagram. Is UNSTABLE.

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

18 Energy Reaction coordinate Reactants Products

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

20 Energy Reaction coordinate Reactants Products Activated Complex or Transition State

21 Energy Reaction coordinate Reactants Products Overall energy change (  H)

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

23 What is  H?  H is the enthalpy, or “heat of reaction.” The amount of energy released or absorbed during a chemical reaction. By convention  H rxn = H products - H reactants

24 What is an exothermic reaction? A reaction that gives off or releases heat. Since...  H rxn = H products - H reactants then  H rxn will be a negative number

25 Energy Reaction coordinate Reactants Products Overall energy change (  H)

26 What is an endothermic reaction? A reaction that absorbs heat. Since…  H rxn = H products – H reactants then  H will be a positive number.

27 Energy Reaction coordinate Reactants Products Overall energy change (  H)

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

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

30 Exothermic vs Endothermic

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

32 MC Q-FACTORS

33 INTERPRETING REACTION COORDINATES handout 1) B 2) A 3) G 4) G 5) A 6) F 7) F 8) F 9) F 10) B 11) E 12) I 13) D 14) J 15) C 16) H 17) H 18) A

34 HEATS OF REACTION MC 1) 1 2) 1 3) 4 4) 2 5) 2 6) 2 7) 2 8) 1 9) 1 10) 4 11) 4 12) 1

35 PE DIAGRAMS FOR RX 1. EXO ENDO SAME 11. H 12. E 13. B 14. G 15. I 16. F 17. A 18. C 19. D


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