Presentation on theme: "Kinetics (Reaction Rate)"— Presentation transcript:
1Kinetics (Reaction Rate) How Fast Does the Reaction Go
2Rates of reaction KINETICS ObjectivesTo understand that a chemical reaction involves collisions between particlesTo be able to describe the four factors which will affect the rate of a chemical reaction.To describe the factor that can not be changed and affect the rate of a chemical reaction.
3Collision TheoryIn order to react molecules and atoms must COLLIDE with each other.They must hit each other with enough energy and with the correct orientation.The more “frequently” the particles hit, the faster the reaction will go.A COLLISION THAT RESULTS IN PRODUCT IS CALLED EFFECTIVE COLLISIONAnything that increase these effective collisions will make the reaction faster.
4How do we make the reaction go faster? There are four things that we can change to make the reaction go faster.TemperatureSurface areaConcentrationUsing a catalyst
5TemperatureWhen we increase the temperature we give the particles energy, this makes them move faster, which means they collide with other particles more often.So the reaction goes faster.
6Surface areaIf we make the pieces of the reactants smaller we increase the number of particles on the surface which can react.This makes the reaction faster.The particles on the surface can reactWhen cut into smaller pieces the particles on the inside can react
7Concentration There are more particles in the same volume to react If we make one reactant more concentrated (like making a drink of orange squash more concentrated)There are more particles in the same volume to reactSo the reaction goes faster.There are less red particles in the same volume so there is less chance of a collisionThere are more red particles in the same volume so there is more chance of a collision so the reaction goes faster
8Factors that Affect Rate 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.Inhibitor- a substance that blocks a catalyst.
9Factors that Affect Rate Summary TemperatureHigher temperature faster particles.More and harder collisions.Faster Reactions.ConcentrationMore concentrated means molecules closed together.Collide more often.Faster reaction.
10Particle sizeMolecules can only collide at the surface.Smaller particles bigger surface area.Smaller particles faster reaction.Smallest possible are molecules or ions.Dissolving speeds up reactions.Getting two solids to react with each other is slow.
11Using a catalystA catalyst is a chemical which is added to a reaction.It makes the reaction go faster.The catalyst does not get used up in the reaction.
12Potential Energy Diagrams Represent the changes in potential energy that occur during a chemical reaction.The reaction coordinate represents the progress of the reaction.
13Remember in terms of energy content HIGH ENERGY =UNSTABLELOW ENERGY = STABLE
14Classification of reactions Exothermic Rx: releases energy. Heat part of the products.Endothermic Rx: absorbs energy. Heat part of the reactants.
15DefinitionsActivation Energy: the minimum amount of energy needed to start up a chemical reaction.Activated Complex: a temporary intermediate product. Highest point of the diagram. Is UNSTABLE.
16Catalyzed ReactionsNeed less energy to start up the reaction. The presence of a catalyst LOWERS THE ACTIVATION ENERGY!!!
18Activation Energy - Minimum energy to make the reaction happen ReactantsProductsReaction coordinate
19Activated Complex or Transition State EnergyReactantsProductsReaction coordinate
20EnergyReactantsOverall energy change (DH)ProductsReaction coordinate
21ThermochemistryThe study of the changes in heat energy that accompany chemical reactions and physical changes.
22What is DH? DH is the enthalpy, or “heat of reaction.” The amount of energy released or absorbed during a chemical reaction.By conventionDHrxn = Hproducts - Hreactants
23What is an exothermic reaction? A reaction that gives off or releases heat.Since...DHrxn = Hproducts - Hreactantsthen DHrxn will be a negative number
24EnergyReactantsOverall energy change (DH)ProductsReaction coordinate
25What is an endothermic reaction? A reaction that absorbs heat.Since…DHrxn = Hproducts – Hreactantsthen DH will be a positive number.
26ProductsEnergyOverall energy change (DH)ReactantsReaction coordinate
27Heats of Reaction Table I The new reference table (Table I) shows different heats of reaction for some common reactions.
28EXOTHERMIC RX Release heat. DH for reaction is negative The value for DH is the amount of heat released during the rxWe write the heat it as PRODUCT in the chemical equationThe greater the magnitude of DH the more stable the product will be!!!!
30ENDOTHERMIC RX Absorb heat DH for reaction is positive The value for DH is the amount of heat absorbed during the rxWe write the heat it as REACTANT in the chemical equationThe greater the magnitude of DH the more UNstable the product will be!!!!