2What is a Chemical Reaction? A chemical reaction is the process by which one or more substances change into one or more new substances.Reactants are the original substances in a chemical reaction.Products are the substances that are created in a chemical reaction.
3Sample Chemical Reaction Video 1 Click for sample reactionVideo 2
4Formula for Reaction2Al + 3Br2 2AlBr3ReactantsProduct
7Chemical Reaction Versus Physical Change chemical change – new substance forms with properties that differ from original substancedensityboiling pointmelting pointphysical change - changes of stateevaporationcondensationmeltingfreezing
8Types of ReactionsA combustion reaction is a reaction of a carbon-based compound with oxygen.Combustion of propane:C3H8 + 5O2 3CO2 + 4H2OCombustion of ethanol:CH3CH2OH + 3O2 2CO2 + 3H2O
10Synthesis ReactionIn a synthesis reaction a single compound forms from two or more reactants.Two elements form a binary compoundC + O2 CO22C + O2 2COTwo compounds form a ternary compoundCaO(s) + H2O(l) Ca(OH)2(s)CO2(g) + H2O(l) H2CO3(aq)
11Example: 2H2 + O2 2H2O Example: C + O2 CO2 Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)reactant + reactant 1 productA + B → ABExample: 2H2 + O2 2H2OExample: C + O2 CO2
12Sample SynthesisClick to see the synthesis of hydrogen and oxygen
13Decomposition Reactions In a decomposition reaction a single compound breaks down, often with the input of energy, into two or more elements or simpler compounds.Decomposition of waterelectricity2H2O(l)O2(g) + 2H2(g)
141 Reactant Product + Product In general: AB A + B Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds1 Reactant Product + ProductIn general: AB A + BExample: H2O 2H2 + O2Example: HgO 2Hg + O2
15Sample DecompositionClick to see the decomposition of ammonium dichromateClick to see the continuation of the decomposition
16Single DisplacementIn a displacement reaction a single element reacts with a compound and displaces another element from the compound.2Al(s) + 3CuCl2(aq) 2AlCl3(aq) + 3Cu(s)Aluminum displaces copper.
17A + BC AC + B (if A is a metal) Zn(s) + HCl(aq) ZnCl2 + H2(g) Single Replacement Reactions occur when one element replaces another in a compound.A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).element + compound product + productA + BC AC + B (if A is a metal)Zn(s) HCl(aq) ZnCl2 + H2(g)
18Sample Single Displacement Click to see the alkali series with water
19Double DisplacementIn a double-displacement reaction two compounds in aqueous solution appear to exchange ions and form two new compounds.One of the products must be a solid precipitate, a gas, or a molecular compound, such as water.HCl(aq) + NaOH(aq) HOH(l) + NaCl(aq)
20Sample Double Displacement Click to see double displacement
21Law of Conservation of Mass Atoms cannot be created or destroyed, in a chemical reaction, they are rearranged.The atoms that make up the reactants are still there in the products – they are just rearranged.The total mass of the reactants must equal the total mass of the products.When balancing equations, reactant atoms equal the atoms on the product side.Cannot change subscripts when balancing equations. Coefficients are used. (Number added to the front of a compound.
22Rates of reaction Objectives To 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.
23Boardworks GCSE Additional Science: Chemistry Rates of Reaction Why are some reactions faster than others?Teacher notesThis illustration contains several discussion points relating to rates of reaction, including:Red characters: these represent particles that have a large amount of kinetic energy and are therefore likely to react.Blue characters : these represent particles that have a small amount of kinetic energy and are therefore unlikely to react (hence why some are asleep).Bumper cars: the collision between two bumper cars represents the large amount of energy released during a reaction.
25Rates of ReactionA chemical reaction involves a collision between particles.The particles collide and make new substancesThe particles which react are called the reactantsThe substances which are made are called the products
26Reactions, particles and collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionReactions, particles and collisionsReactions take place when particles collide with a certain amount of energy.The minimum amount of energy needed for the particles to react is called the activation energy, and is different for each reaction.The rate of a reaction depends on two things:the frequency of collisions between particlesthe energy with which particles collide.Teacher notesSee the ‘Energy Transfer’ presentation for more information on activation energy.If particles collide with less energy than the activation energy, they will not react. The particles will just bounce off each other.
27Changing the rate of reactions Boardworks GCSE Additional Science: ChemistryRates of ReactionChanging the rate of reactionsAnything that increases the number of successful collisions between reactant particles will speed up a reaction.What factors affect the rate of reactions?increased temperatureincreased concentration of dissolved reactants, and increased pressure of gaseous reactantsincreased surface area of solid reactantsuse of a catalyst.
28Boardworks GCSE Additional Science: Chemistry Rates of Reaction Slower and slower!Reactions do not proceed at a steady rate. They start off at a certain speed, then get slower and slower until they stop.As the reaction progresses, the concentration of reactants decreases.This reduces the frequency of collisions between particles and so the reaction slows down.0%25%50%75%100%percentage completion of reactionreactantsproduct
29Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notesThis animated graph summarizes the qualitative information provided by the gradient of a graph that plots amount of product in a reaction against time.
30Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notesThis animated graph follows-on from the graph on the previous slide, and illustrates how the change in the rate of a reaction can be explained in terms of changing amounts of reactants and product.
31Temperature and collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionTemperature and collisionsHow does temperature affect the rate of particle collision?
32TemperatureWhen we increase the temperature we give the particles energyThis makes them move fasterThis means they collide with other particles more oftenSo the reaction goes faster.
33Temperature and particle collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionTemperature and particle collisionsTeacher notesThis simulation illustrates how increasing the temperature increases the number of collisions between particles.
34Surface 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
35Effect of surface area on rate of reaction Boardworks GCSE Additional Science: ChemistryRates of ReactionEffect of surface area on rate of reactionAny reaction involving a solid can only take place at the surface of the solid.If the solid is split into several pieces, the surface area increases. What effect will this have on rate of reaction?low surface areahigh surface areaThis means that there is an increased area for the reactant particles to collide with.The smaller the pieces, the larger the surface area. This means more collisions and a greater chance of reaction.
36Surface area and particle collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionSurface area and particle collisionsTeacher notesThis simulation illustrates how increasing the surface area increases the number of collisions between particles and solid reactants
37Concentration 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
38Bell Work 11/28 What does a reaction rate tell you? What 5 factors affect reaction rates?How does a catalyst make a reaction go faster?
39Bell Work Review1. How fast a chemical reaction is going. 2. Temperature, concentration, surface area, stirring and catalysts (pressure can also be listed). 3. By lowering the activation energy.
40Effect of concentration on rate of reaction Boardworks GCSE Additional Science: ChemistryRates of ReactionEffect of concentration on rate of reactionThe higher the concentration of a dissolved reactant, the faster the rate of a reaction.Why does increased concentration increase the rate of reaction?At a higher concentration, there are more particles in the same amount of space. This means that the particles are more likely to collide and therefore more likely to react.lower concentrationhigher concentration
41Concentration and particle collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionConcentration and particle collisionsTeacher notesThis simulation illustrates how increasing the concentration increases the number of collisions between particles.
42Effect of pressure on rate of reaction Boardworks GCSE Additional Science: ChemistryRates of ReactionEffect of pressure on rate of reactionWhy does increasing the pressure of gaseous reactants increase the rate of reaction?As the pressure increases, the space in which the gas particles are moving becomes smaller.The gas particles become closer together, increasing the frequency of collisions. This means that the particles are more likely to react.lower pressurehigher pressure
43Using 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.It gives the reaction the energy to get started
44Boardworks GCSE Additional Science: Chemistry Rates of Reaction What are catalysts?Catalysts are substances that change the rate of a reaction without being used up in the reaction.Catalysts never produce more product – they just produce the same amount more quickly.reaction (time)energy (kJ)Ea without catalystDifferent catalysts work in different ways, but most lower the reaction’s activation energy (Ea).Ea with catalystTeacher notesSee the ‘Energy Transfer’ presentation for more information on activation energy.
46Boardworks GCSE Additional Science: Chemistry Rates of Reaction Catalysts in industryWhy are catalysts so important for industry?Products can be made more quickly, saving time and money.Catalysts reduce the need for high temperatures, saving fuel and reducing pollution.Teacher notesSee the ‘Enzymes’ Biology presentation for more information on enzymes as catalysts and their use in industrial processes.Catalysts are also essential for living cells. Biological catalysts are special types of protein called enzymes.