Grade_10_Unit_7_Kinetics_MAH_(NXPowerLite) Opp

Grade_10_Unit_7_Kinetics_MAH_(NXPowerLite) Opp - Grade 10...

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Unformatted text preview: Grade 10 Rates of Chemical Grade reactions or Kinetics reactions •100’s of free ppt’s from www.pptpoint.com library Compiled by MAH 1 Essential Understandings Describe what is meant by rate of reaction Explain Collision Theory Identify Activated complex and activation energy Understand which factors affect the rate of a chemical reaction and explain these in terms of Collision Theory Interpret energy –v­ reaction profile diagrams Energy distribution diagrams (Maxwell Boltzmann diagrams) 2 Define the term rate of reaction Define rate and describe the measurement of reaction rates. reaction Rate of reaction can be defined as the decrease in the concentration of reactants per unit time or the increase in the concentration of product per unit time. Rate of reaction is a measure of the rate at which products are formed = rate at which the reactants are consumed 3 Rate of a reaction The rate value will vary according to the number of moles of the substance (coefficients in a balanced equation) For example N2 + 3H2 = 2NH3 The rate at which nitrogen disappears = 3X rate at which hydrogen disappears = 2X rate at which ammonia appears. Rate graph simulation http://www.chm.davidson.edu/ChemistryApplets/ kinetics/RateOfReaction.html 4 What does a real reaction look like ? V olum e o f C O 2 T im e What is happening to the rate of the reaction with time? How can we find the rate at any instant 5 The rate of a reaction varies over time so an instantaneous rate is the slope of the tangent at a particular instant The rate of reaction decreases over time because the properties of reactants decrease as the reaction progresses The graph for rate of reaction for reactant loss is opposite of this graph (as [p] increases, [r] decreases 6 Collision Theory Collision – IMPORTANT – NOT ALL COLLISIONS WILL LEAD TO A REACTION! – Some are duds 7 Why do some collisions not Why produce a reaction? 8 Reasons Behind the Theory Reasons When particles approach each other there is repulsion between the electron ­ clouds The collision must have sufficient ENERGY for the reaction to occur ENERGY must break some bonds in the particles before the reaction takes place 9 Sufficient ENERGY 10 10 Collisions that cause Reactions Collisions A minimum energy, called the activation energy is needed for a particular reaction 11 11 Definition Definition The activation energy is the energy required to achieve the transition state and form the activated complex The transition state is at the top of the curve Any collisions which do not equal or exceed the activation energy will be duds 12 12 Activation Energy 13 13 Exothermic and Endothermic Exothermic reactions reactions ΔH positive Endothermic reactions take in heat from the surroundings. The surroundings get cold ΔH negative Exothermic reactions give out heat to the surroundings which get hot 14 14 Please Notice The Activation energy, given the symbol EA, is measured from the starting level to the top of the ‘hill’ The energy change of the reaction, shown a delta energy, more correctly ΔE or ΔH, is measured from the starting or H, is measured from the starting level to the finishing level 15 15 Collision Theory Collision Particles have to collide to react. If they collide, with enough energy then they will react. The minimum amount of kinetic (movement) energy that two particles need if they are going to react when they collide is called the activation energy. 16 16 Factors affecting rate Factors Concentration in terms of Collision Theory Particle size of solids clearly if the same of solid is used but the particles are smaller (bigger surface area) there will be more places for reaction Temperature: clearly particles will have a higher collision energy at higher temp. and more successful collisions. 17 17 Concentration Higher the concentration the more particles, the more collisions video 18 18 Fact 1: An increase in the concentration of a solution, Fact or the pressure of a gas, results in an increase in the reaction rate reaction Explanation: If the concentration of a solution, or the pressure of a gas, is increased, then there are more particles in a given volume. Therefore there will be more collisions in a set amount of time and the probability of more successful collisions becomes higher. As a result the reaction rate will increase. 19 19 20 20 Fact 2: An increase in surface area of a solid results Fact in a increase in the rate of a reaction. in Explanation: If the surface area of a solid is increased, there are more particles exposed to the other reactant. Therefore there will be more successful collisions in a set amount of time and the rate increases 21 21 Temperature effect and collisions The increased Kinetic Energy of collisions at higher temperatures only accounts for a small proportion of the increased rate. On average a 10oC rise doubles the rate of a reaction. The major reason for this is the proportion of particles, at a higher temperature, which now have an energy greater than the Activation energy. 22 22 23 23 24 24 Temperature Higher temperatures equals faster moving molecules which equal more collisions per sec. video 25 25 Fact 3: An increase in temperature results in an Fact increase in reaction rate. increase Explanation: If the temperature is increased, the average kinetic energy of the particles increases. There is therefore a greater chance of more collisions having an energy greater than the activation energy and reaction rate increases. Also (less importantly) because particles are moving faster, there will be more collisions in a given time, therby increasing the rate 26 26 Catalysts A catalyst is a substance that speeds up a reaction without being used up itself. Some reactions have catalysts that can speed them up, but for many reactions there is no catalyst that works. 27 27 Catalyts (Enzymes) Grade 10: A catalyst is a substance that increases the rate of a reaction but is not used up by the reaction. SL and HL ­level: Catalysts affect the rate of a reaction by providing an alternative reaction pathway with a lower activation energy 28 28 29 29 Activation Energy with catalyst 30 30 Fact 4: Addition of a catalyst can lead to an increase Fact in reaction rate in Explanation: A catalyst acts by enabling a reaction to proceed via a route of lower activation energy. There will therefore be more collisions of sufficient energy to cause a reaction to occur, and rate will increase 31 31 SUMMARY 32 32 Summary.What effects rate of Summary.What reaction? Concentration ↑ Rate of Collision ↑ Surface area ↑ Rate of Collision ↑ – Only reactions that involve substances in phases that do NOT mix Temp.↑ molecule energy &collisions↑ Catalyst lead to lower activation ENERGY = more proportional collisions 33 33 THE END 34 34 ...
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This note was uploaded on 11/17/2011 for the course PHYS 121 taught by Professor Burgeson during the Fall '11 term at BYU.

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