Chemical Reactions Chemical reactions occur every minute of every day Some are very fast such as the reaction of sodium with water Others are very slow such as iron rusting Some are somewhere inbetween such as milk going sour ID: 1042865
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1. S4 ChemistryN4/5 Rates of Reaction
2. Chemical ReactionsChemical reactions occur every minute of every day. Some are very fast, such as the reaction of sodium with water. Others are very slow, such as iron rusting. Some are somewhere in-between, such as milk going sour.
3. Evidence of a Chemical ReactionA chemical reaction involves the formation of new substances. Reactants Products Chemical reactions happen everywhere. Digesting food in the body. Burning gasses in air. Precipitate formed.
4. Identifying a Chemical ReactionElements in the periodic table react together to form the many different compounds around us.A chemical reaction has taken place when one or more of the following signs are observed.Colour change.Gas given off.Solid formed when two solutions are mixed.Heat and light are produced.A new substance is always formed.
5. ConclusionWhen the reactions took place, there was a new product formed in each one. There were also some signs such as a colour change, glowing and gas being given off (effervescence).A reaction has taken place when a new product is formed. The reaction is not easily reversible.
6. Collision TheoryIn order for a chemical reaction to occur, the atoms or molecules need to make contact with each other. A chemical reaction only occurs when a successful collision occurs. From S3, we know that a reaction can be sped up by:Increasing the surface area of a reactant (increase surface area).Increasing the concentration of a reactant. Increasing the temperature. Use of a catalyst.
7. Collision Theory - NoteIn order for a chemical reaction to occur, the atoms or molecules need to make contact with each other. A chemical reaction only occurs when a successful collision occurs. Reactions can be sped up by:Increasing the temperatureIncreasing the concentrationDecreasing the particle sizeUse of a catalyst
8. Chemical ReactionsWe’re going to move away from the idea of chemical reactions being “fast” or “slow”. We are now going to think of the rate of chemical reactions. The rate of a chemical reaction is defined as: The change in the concentration of a reactant or product over a period of time. It can be expressed by the mathematical equation:Rate = change Time
9. Chemical ReactionsThe change can be:Change in concentrationChange in temperatureChange in volume of gas produced during a reactionMeasuring the loss in mass during a reaction
10. Chemical Reactions – Factors Affecting RateA number of factors can affect the rate of a chemical reaction (how “fast” or “slow” it goes).Concentration of reactants. Particle size.Temperature. Presence of a catalyst.
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12. Measuring the Rate of ReactionYou’re going to measure the rate of a reaction by collecting the volume of gas produced as a reaction proceeds. Copy table on board
13. Measuring the Rate of Reaction - NoteTo calculate the rate of a chemical reaction, we use the following equation:Rate = Where: ΔQ = change in mass, concentration, volume of gas,… Δt = change in time
14. Example (copy table into jotter)Below shows the volume of gas produced during a reaction. Calculate the rate of reaction:Between 0 and 10 secondsBetween 0 and 20 secondsBetween 40 and 50 secondsBetween 50 and 60 secondsBetween 60 and 70 secondsTime (seconds)Volume of Gas Produced (cm3)001021204130554072507960817081
15. Measuring the Rate of Reaction -
16. Measuring the Rate of Reaction – Collect Gas Apparatus: Test tube with rubber tubing, beehive, basin of water, 100 cm3 measuring cylinder, 1.0 mol L-1 HCl, a few lumps of CaCO3, timer.Method: Collect apparatus and set up as shown on board.Add 10 cm3 1.0 mol L-1 HCl. When you are ready, add the CaCO3 lump and quickly place the stopper on. Place the tubing under the beehive. Start the timer and measure the volume of gas every 30 seconds, for about 10 minutes. Draw a scatter plot of your results on the graph paper provided, do not join the dots.
17. Measuring the Rate of Reaction – Demo. We’ve measured the rate of a reaction by collecting the gas over water. We can also do this using a piece of apparatus called a gas syringe.
18. Measuring The Rate of Reaction - MassYou’re now going to measure the rate of reaction by measuring the change in mass during a reaction. You’ll use an accurate balance to do so. Copy the table on the board and diagram.
19. Rate of Reaction – Methods of MonitoringThere are a number of different methods we can use to monitor the rate of a chemical reactionVolume of gas producedTemperaturepHPressureElectrical conductivity
20. Rate CalculationsYou need to be able to calculate the rate of a chemical reaction over a period of time. The equation you use is:Rate = ΔQ = change in temperature/volume of gas/concentration… Δt time
21. TaskFrom your experiments last week, draw a scatter graph of your results. Remember to include:-ScaleLabels and unitsPlotting – Do not join up points. Draw a smooth curve.
22. Rates of ReactionWe can draw lines on a rate of reaction graph to show a change in conditions (e.g. temperature, concentration or particle size). Note:A reaction occurs when there is a successful collision between reactant atoms. The atoms must collide with enough energy to form the product.
23. Open QuestionsIn the National 5 exam paper, you will have to answer two extended response questions. Each of these is worth three marks. They include the phrase “using your knowledge of chemistry…” in the stem of the question.
24. Open Questions - ActivityWe’re going to do a co-operative activity where you need to discuss what information you would include when answering such a question.On the flip-chart paper, write down what you would include in an answer to the following questions. Social intention: participating equally, listening actively, sharing ideas, staying on task.
25. Open Question A pupil conducted an experiment and concluded:“the only way to speed up a reaction is to increase the temperature”Using you knowledge of chemistry, comment on the accuracy of the pupil’s statement.
26. Open QuestionA pupil had four unknown metals. Using your knowledge of chemistry, how could the pupil rank them in order or reactivitiy.
27. Open Question - 2016A group of pupils were given strips of aluminium, iron, tin and zinc. Using your knowledge of chemistry, suggest how the pupils could identify each of the four metals.
28. Open Question - 2014A pupil reacted potassium permanganate with oxalic acid, C2H2O4.2MnO4-(aq) + 5C2H5O4(aq) + 6H+ (aq) 2Mn2+ (aq) + 10CO2(g) + 8H2O(l)Using your knowledge of chemistry, comment on how the pupil could have determined the rate of reaction.
29. Rates of Reaction - QuestionThe graph below illustrates the rate of reaction where Magnesium ribbon reacts with 1 mol L-1 HCl at 30oC.Copy the graph and add lines to show:Mg powder reacting with 1 mol L-1 at 30oCMg powder reacting with 1 mol L-1 at 15oCLabel each line
30. Rates of reaction Complete the questions on pages 6, 7 and 8 of the blue workbook.