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1 of 35© Boardworks Ltd 2009
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3 of 35© Boardworks Ltd 2009 What is collision theory? Collision theory states that for a reaction to occur: particles must collide with the correct orientation. particles must have sufficient energy particles must collide Most collisions do not result in reaction because they do not meet the second and third criteria.
4 of 35© Boardworks Ltd 2009 Activation energy
5 of 35© Boardworks Ltd 2009 Effect of surface area on collisions Only the particles on the surface of a solid will collide with particles of the other reactant. Surface area can be increased by decreasing the size of the reactant particles. Powders have a very large surface area. increasing surface area If the surface area is increased, more particles will be on the surface and able to collide with particles of the other reactant. This means that there will be more collisions in total and therefore more reactive collisions.
6 of 35© Boardworks Ltd 2009 Reaction of marble chips with acid The effect of changing surface area on the rate of reaction can be explored by reacting marble (calcium carbonate) chips and an acid such as 2 mol dm -3 hydrochloric acid. CaCO 3(s) + 2HCl (aq) CaCl 2(s) + CO 2(g) + H 2 O (l) The carbon dioxide gas evolved can be collected and its volume measured over time. The rate at which it is produced is a measure of the rate of reaction. By repeating the experiment with marble chips of different sizes, the effect of surface area on the rate of reaction can be examined.
7 of 35© Boardworks Ltd 2009 Effect of surface area on rate: graph
8 of 35© Boardworks Ltd 2009 Effect of concentration on rate
9 of 35© Boardworks Ltd 2009 Effect of concentration on rate: graph
10 of 35© Boardworks Ltd 2009 Effect of gas pressure on rate
11 of 35© Boardworks Ltd 2009 Effect of pressure on rate: graph
12 of 35© Boardworks Ltd 2009 Effect of temperature on particles
13 of 35© Boardworks Ltd 2009 Effect of temperature on rate Increasing the temperature of the reaction mixture increases the rate of reaction in the following two ways: 1. At higher temperatures, the particles are moving faster, so collide more frequently. A higher number of collisions in total means a higher number of successful collisions. 2. At higher temperatures, a higher proportion of the molecules have the activation energy or more. This means that a higher proportion of collisions is successful.
14 of 35© Boardworks Ltd 2009 Effect of temperature on rate: graph
15 of 35© Boardworks Ltd 2009 Collision theory summary
16 of 35© Boardworks Ltd 2009 Rate of reaction summary
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18 of 35© Boardworks Ltd 2009 Distribution of particle speeds
19 of 35© Boardworks Ltd 2009 Energy distribution curves
20 of 35© Boardworks Ltd 2009 The effect of changing temperature
21 of 35© Boardworks Ltd 2009 Small temperature changes The Maxwell–Boltzmann distribution shows that for a small increase in temperature, there is a relatively large increase in the number of particles with at least the activation energy. A small increase in temperature therefore leads to a large increase in rate. The increase in collision frequency is also a factor, but its effect is small compared to the increase in energy. no. of particles energy EaEa no. particles with E a almost doubled
22 of 35© Boardworks Ltd 2009 Effect of temperature summary
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24 of 35© Boardworks Ltd 2009 Effect of catalysts on rate: graph
25 of 35© Boardworks Ltd 2009 What do catalysts do?
26 of 35© Boardworks Ltd 2009 How do catalysts work? An example is the oxidation of sulfur dioxide: SO 2(g) + V 2 O 5(s) SO 3(g) + V 2 O 4(s) The catalyst is re-formed by reacting with oxygen: V 2 O 4(s) + ½O 2(g) V 2 O 5(s) SO 2(g) + ½O 2(g) SO 3(g) This is catalyzed by vanadium(V) oxide: Catalysts increase the rate of reactions without being used up during the reaction. One way in which this occurs is for the catalyst to be changed during the reaction, then changed back in a second reaction with one of the reactants or products. This is an alternative reaction pathway.
27 of 35© Boardworks Ltd 2009 Catalysts and energy distribution curves
28 of 35© Boardworks Ltd 2009 Heterogeneous catalysts There are two types of catalysts: heterogeneous and homogeneous. Heterogeneous catalysts are in a different phase to the reactants. The catalyst is usually a solid and the reactants are liquids or gases (e.g. solid catalysts for gas reactions in catalytic converters). Industrial examples of heterogeneous catalysis include the iron catalyst used in ammonia production and the Ziegler–Natta catalyst used in poly(e)thene production.
29 of 35© Boardworks Ltd 2009 Homogeneous catalysts Homogeneous catalysts are in the same phase as the reactants. The catalyst and the reactants are usually liquids, such as the hardener added to fibreglass resin. Another example of homogeneous catalysis is the destruction of atmospheric ozone catalyzed by chlorine free radicals. In this reaction the catalyst and reactants are in the gas phase.
30 of 35© Boardworks Ltd 2009 Advantages of catalysts Using a catalyst means that a reaction can take place at the same rate as the uncatalyzed reaction, but at a lower temperature and/or pressure. This has the following advantages, which are particularly important in industry: A non-industrial example is enzyme catalysis in biological washing powders, allowing efficient washing at a lower temperature. lower energy demands… …therefore less CO 2 produced… …therefore less environmental impact… …and lower production costs.
31 of 35© Boardworks Ltd 2009 Catalysts: true or false?
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33 of 35© Boardworks Ltd 2009 Glossary
34 of 35© Boardworks Ltd 2009 What’s the keyword?
35 of 35© Boardworks Ltd 2009 Multiple-choice quiz
Title: Lesson 2 Collision Theory and Maxwell-Boltzmann Distribution Learning Objectives: – Understand the four main influences on the rate of a reaction.
1 of 39© Boardworks Ltd Kinetics. 8.1a Collision Theory Learning Objectives 1.Understand that reactions can only occur when collisions take place.
1 of 39© Boardworks Ltd of 39 © Boardworks Ltd of 39 What does rate of reaction mean? The speed of different chemical reactions varies.
Unit 9 – Reaction Rates and Equilibrium The area of chemistry that concerns reaction rates (how fast a reaction occurs)
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1 of 39© Boardworks Ltd 2007 Kinetics. © Boardworks Ltd of 39.
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© Boardworks Ltd of 49 KS4 Chemistry Rates of Reaction.
Kinetics HL and SL Collision Theory For a reaction to occur 1.particles must collide 2.with enough energy 3.in the correct orientation Not all.
Increasing the concentration of a reactant substance will increase the rate of reaction. This is because more collisions will occur, and therefore more.
Collision Theory Section 6.1 (continued). Collisions Vital for chemical change Provides the energy required for a particle to change Brings the reactants.
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Reaction Rates Ch 18 Notes. Collision Theory 1.Reacting substances (atoms, ions, molecules, etc.) must collide in order to react 2.Collisions have to.
Collision Theory In order for a reaction to occur, reactant particles must collide with each other. In order for a reaction to occur, the collisions must.
Noadswood Science, To be able to measure the rate of reaction Tuesday, September 08, 2015.
Thermodynamics Tells if a reaction will occur.. Kinetics Tells how fast a reaction will occur.
RATES OF REACTION. Rates of Reaction The rate of a chemical reaction is the speed at which the reaction occurs (i.e. speed at which the reactants are.
Factors Affecting the Rate of a Chemical Reaction The following events must occur before a reaction can proceed: 1.The reactant particles must collide.
TOPIC A FACTORS AFFECTING RATES OF REACTION. Factors that influence the rate of a chemical reaction. Each factor has a noticeable effect on the microscopic.
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Reaction Rates, Catalysts and Collision Theory. Rates of reaction The rate of a reaction measures how fast it happens. Increased reaction rate means that.
Topic 4. Collision theory Chemical reactions only occur when reacting particles collide with each other with sufficient energy. The minimum amount of.
Catalyst. What is catalyst function? Catalyst function is providing an alternative reaction pathway with lower activation energy so that more reaction.
Standard 8: Reaction Rate Chemistry Ms. Siddall. Reaction rate = speed of reaction Example An explosion happens quickly Rusting happens slowly 8a: Measuring.
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© Boardworks Ltd of 11. © Boardworks Ltd of 11 What are enzymes? Enzymes are biological catalysts – they speed up the chemical reactions that.
Calcium carbonate (marble) hydrochloric acid carbon dioxide.
REACTION KINETICS (AS) 1.Rate of reaction = change in concentration of reactant or product over time Rate of reaction = [reactant]/ time OR [product]/
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