Presentation on theme: "Chemical Kinetics Chemical Energy— results from the particular arrangement of atoms in a chemical compound; heat and light produced in this reaction due."— Presentation transcript:
1 Chemical KineticsChemical Energy— results from the particular arrangement of atoms in a chemical compound; heat and light produced in this reaction due to energy released during the breaking and reforming of chemical bonds
4 Decomposition of Nitrogen Triiodide Molecules store energy (chemical potential energy) in the bonds that hold them together. When the bonds are broken, energy is released.2 NI3(s) N2(g) I2(g)
5 Collision Theory Describes how a reaction proceeds. The molecules have to “collide” with the correct energy and orientation in order to create a new compound.Ineffective Collision(no reaction occurs)Effective Collision(reaction occurs)
6 Potential Energy Diagrams Shows the PE of the components of a chemical reaction.activatedcomplexactivationenergyEareactantsproductsenergycourse of reactionAnimation by Raymond ChangAll rights reserved
7 H, Enthalpy heat content of a substance: natural systems tend to go from a state of higher energy to a state of lower energy. For instance, a ball rolls down a hill spontaneously, but not up. The ball looses potential energy as it rolls downhill. At the bottom of the hill it has zero potential energy. This same idea can be applied to chemical potential.
8 Potential energy kinetic energy kinetic energy Energy in Energy out The energy something possesses due to its motion, depending on mass and velocity.
9 Potential Energy Diagram Concepts Enthalpy of Reaction – a measure of the heat energy absorbed or released by a reaction system in the form of its products:∆Hrxn = Hproducts – HreactantsActivated Complex – a short lived, unstable arrangment of atomsReaction rate - the rate at which products form or reactants are used up.Activation energy - the energy needed to start a chemical reaction.
10 Exothermic Reaction Reactants Products + Energy Energy Reactants -DH 10 energy = energy energyactivatedcomplexEnergy of reactantsActivationEnergyEnergy of productsEnergyReactants-DHProductsReaction Progress
11 Exothermic Reaction A reaction that releases energy. The reactants have more energy than the products.Energy must be released as the products form.The container in which an exothermic reaction is taking place will feel hot.
12 Endothermic Reaction +DH Endothermic Energy Reaction progress Energy + Reactants ProductsactivatedcomplexActivationEnergyProductsEnergy+DH EndothermicReactantsReaction progress
13 Endothermic Reaction A reaction that absorbs energy. The products have more energy than the reactants.Energy must be absorbed as the products form.The container in which an endothermic reaction is taking place will feel cold.
14 Effect of Catalyst on Reaction Rate What is a catalyst? What does it do during a chemical reaction?Catalyst lowers the activation energy for the reaction.EnergyReaction Progressproductsactivation energyfor catalyzed reactionNo catalystreactantsA catalyst lowers the activation energy for the reaction. This allows the reaction to occur at a much faster rate.The catalyst is not a reactant or product. It is not consumed during the chemical reaction.
15 Chemical Reaction Rates Reaction rate refers to one or more of the following:* The rate of disappearance of one of the reactants.* The rate of appearance of one of the products.Different chemical reactions take place at different rates.The study of reaction rates is the study of the forming and breaking of chemical bonds, a very complex subject.
16 Chemical Reaction Rates The nature of the reactants involved in a chemical reaction will determine the kind of bonding that occurs.Reactions with bond rearrangement or electron transfer (covalent) generally take longer than ionic reactions.Ionic reactions are almost instantaneous because of the strong attraction between the charged particles.
17 Other factors affecting reaction rate: Concentration - For a chemical reaction to occur, the particles must collide.An increase in the number of particles per unit volume (concentration) increases the chance of their colliding. Increasing the concentration of the reacting particles generally increases the reaction rate.
18 Other factors affecting reaction rate: lower temperaturehigher temperatureminimum energyfor reactionFractions of particlesKinetic energy
19 Other factors affecting reaction rate: Temperature - An increase in the speed of molecules increases the number of molecules that have the required activation energy. Increasing the number of molecules with activation energy generally increases the reaction rate.Surface Area – more surface area, faster reaction
20 Other factors affecting reaction rate: Catalysts - A catalyst is a substance that increases a reaction rate without being permanently changed. The catalyst appears to be chemically unaffected by the reaction. A catalyst changes the reaction mechanism in such a way that the activation energy required is less than that in the uncatalyzed reaction.EnergyReaction Progressproductsactivation energyfor catalyzed reactionNo catalyst
21 Other factors affecting reaction rate: Inhibitors - An inhibitor ties up a reactant in a complex so that it will not react.