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Investigation into what affects the rates of a reaction.

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Introduction

Investigation into what affects the rates of a reaction Background Information Reactions occur when particles of different elements or compounds collide, and react together. The particles need a certain amount of energy for the collisions to be effective. Particles can gain energy by collisions. Only collisions with enough energy are effective enough to cause a reaction. The minimum amount of energy needed for a reaction to happen when the particles collide is called the activation energy. This diagram shows the activation energy of a reaction. As you can see, the reactants have a certain amount of energy, through collisions they increase the amount of energy. At the activation energy the reactants start to react, this makes them lose energy as they turn into the products which have even less energy. For a reaction to happen the particles must overcome this energy barrier. Several factors can change the amount of energy each particle has, or the amount of energy needed to overcome this barrier. These factors change the rate of reaction. Factors which change rate of reaction Temperature Increasing the temperature increases the rate of reaction, because particles collide more frequently and with more energy. As the temperature is increased, the particles present have more energy. This has two effects: 1- The particles move around faster and collide more often- this slightly increases the reaction rate. 2- Because the particles have more energy, any collisions are more likely to result in particles reacting- this has a considerable effect on reaction rate. An example of temperature affecting reaction rate can be shown in the reaction between sodium thiosulphate and hydrochloric acid- increasing the temperature by just 10 degrees C can double the reaction rate. Concentration Increasing the concentration of solutions will increase reaction rate because more particles are present in the same volume, so they are closer together and will collide more often to react. ...read more.

Middle

� Be careful when handling chemicals not to spill any � If any chemicals get on your skin wash thoroughly � Make sure equipment is not damaged or broken Fair Test During the whole of this investigation I will make tests fair by keeping everything apart from one variable exactly the same. This includes: � Using the same size and shape of flask each time, so the timing for when the cross disappears can be measured more accurately and fairly. � Trying to keep the room temperature the same so temperature doesn't affect my results. � The same person doing all of the timing, because their reactions for when the cross disappears should be constant. � Using the same overall volume of liquid in each test. � Using separate measuring cylinders for each solution, sodium thiosulphate, hydrochloric acid and water, so they do not contaminate each other. Method 1) Set up the equipment as shown in the diagram below: 2) Measure out 25 cm3 of sodium thiosulphate in one measuring cylinder, and 25 cm3 of hydrochloric acid in another measuring cylinder, try to make these measurements as accurate as possible to the nearest ml. 3) Add the two chemicals into the conical flask at the same time. 4) Start the stopwatch as the chemicals are added together, and time how long it takes for the cross to disappear. Measure the time to the nearest 0.01-second, this should be fairly accurate. 5) Record the result. 6) Wash out the conical flask ready for the next reaction, so there is no contamination from the previous one. 7) Repeat the reaction three times at each concentration. This will make the results more reliable, and will show any anomalous results, this makes the experiment much more accurate. 8) Dilute the sodium thiosulphate, using water to keep the volume constant at 25 cm3. This will make the experiment a fair test. ...read more.

Conclusion

Changing the temperature could give the particles less or more energy, depending on which way it went, thus making the reaction faster or slower, making the overall results less accurate. A different approach to this experiment that would still show similar results is using data logging equipment to test the rate of reaction. This could be done by putting a light source on one side of the flask in which the reaction will take place, and putting light sensor on the other side. As the reaction takes place the amount of light passing through the flask will slowly decrease, and by using data logging equipment this amount of light passing through could be plotted against time on a graph, to show a similar pattern of results as the concentration changes. This may be more accurate than getting someone to time the reaction, because there is no time delay because of the timing persons reactions, and also the experiment stops at exactly the same point each time. Further work that would provide additional information about the reaction between sodium thiosulphate and hydrochloric acid and reaction rates in general, is an experiment to test a different variable. For example you could carry out an experiment to test how temperature affects the rate of this reaction. This would be done by heating up both reactants in a water bath before the reaction, and then when they are at the correct temperature, putting them together, and timing the reaction in a similar way as in this experiment. I would use a range of 5 temperatures, 25 C (room temperature), 35 C, 45 C, 55 C and 65 C. This would give me a good range. I would fill in a results table as shown below: Temperature of Time for reaction to take place (seconds) Reactants ( C) Test 1 Test 2 Test 3 Average 25 35 45 55 65 This document was downloaded from Coursework.Info - The UK's Coursework Database Click here to visit Coursework.Info/ Alice Palmer Chemistry Coursework Mrs Greenwood 1 ...read more.

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