3 Chapter 14 Chemical Reactions Section 4 Energy and Rates of Reactions Section OutlineReactions and Energy- Exothermic reactionsFigure 1. Types of Chemical Reactions-Law of Conservation of EnergyFigure 2. No titleRates of Reaction- Activation energyFigure 3. No title-Sources of Activation EnergyFigure 4. Energy Diagrams
4 Chapter 14 Chemical Reactions Section 4 Energy and Rates of Reactions Section Outline (cont.)Factors Affecting Rate of Reaction- TemperatureFigure 5. No title- ConcentrationFigure 6. Concentration of solutions- CatalystFigure 7. No title
5 Reactions and EnergyChemical energy is part of all chemical reactions.Energy is needed to break chemical bonds in reactions.Energy is released when new chemical bonds form in chemical reactions.
6 Reactions and EnergyExothermic reaction – a chemical reaction that releases energyExo means “go out” or “exit”Endothermic reaction – a chemical reaction that takes energy inEndo means “go in”
7 Demonstration 1 – Energy Release Types of Energy releaseLightElectrical energyLight and thermal energy
8 Demonstration 1 – LightSnapping a glowstick breaks a small glass container in the glowstick, allowing chemicals in the glass container to mix with chemicals outside the glass (but inside the chamber of the glowstick).The resulting reaction givesoff light.
9 Demonstration 2 – Electrical Energy Electrical energy is released in anexothermic reaction that takes placein the batterySee if the batteries get warm.2 MnO2(s) + 2 H2O(l) + Zn(s) 2 MnO(OH)(s) + Zn(OH)2(s)
10 Demonstration 3 – Heat and Light Release Energy is released during some chemical reactions. The fire of a Bunsen burner gives off light energy and chemical energy. (An alcohol burner, candle, lighter, etc. could also be used, although reaction would change.)CH4 + 2 O2 CO2 + 2 H2O
11 Signs of Chemical Reactions Gas formationSolid (precipitate) formationColor changeEnergy changeLightThermal energy (heat)Electrical energy
12 Law of Conservation of Energy Law of conservation of energy – energy cannot be created or destroyedEnergy can change formsEnergy can be transferred from oneobject to another in the same mannerthat a baton is transferred from onerunner to another in a relay race.
13 Rates of ReactionActivation energy – smallest amount of energy that molecules need to react.Chemical reactions need energy to get startedIn the same way that a bowling ball needs a pushto get rolling.
14 Activation Energy Activation energy Reactants Energy Activation energy givenoffEnergyabsorbedProductsReaction progressReaction progress
15 Factors Affecting Rates of Reaction Demonstration 4 – Glow Sticks TemperatureA higher temperature causes a faster reaction rate.At higher T, particles of reactants move rapidly.Rapid movement causes particles to collide often and with a lot of energy.Many particles have the activation energy to react and change into products in a short time.The light stick on the right glows brighterthan the one on the left because the oneon the right is warmer.
16 Factors Affecting Rates of Reaction ConcentrationIn general, a high concentration of reactants causes a fast rate of reaction.Concentration is a measure of the amount of one substance dissolved in another substance.When the concentration is high, there are many reactant particles in a given volume and a small distance between them.Thus, the particles run into each other often, leading particles to react faster.
17 Factors Affecting Rates of Reaction Surface AreaSurface area is the amount of exposed surface of a substanceIncreasing surface area increases rate of reaction.Greater surface area exposes more particles of the reactant to other reactant particles.These leads to more collisions and faster rates.
19 Factors Affecting Rates of Reaction InhibitorsAn inhibitor is a substance that slows down or stops a reactionFood preservatives – slow down growth of bacteria and fungi
20 Factors Affecting Rates of Reaction CatalystsCatalyst – speeds up a chemical reaction without being consumed/A catalyst is not consumed because it is not a reactant.A catalyst lowers the activation barrier, which allows a reaction to happen more quickly.This catalytic converter contains platinum andpalladium. These two catalysts increase the rateof reactions that make the car’s exhaust lessharmful.
21 Demonstration 6 – Catalyst Hydrogen peroxide, H2O2, is unstable but decomposes very slowly. The decomposition reaction gives off heat. If Cu2+ ions are added (as a catalyst) to add aqueous solution of H2O2, the reaction proceeds rapidly and can become hot enough to boil the water.If dishwashing detergent is added to the solution before the catalyst, then a version of the elephant toothpaste demonstration is produced.2 H2O2 O2 + 2 H2O