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Rates of reaction.

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Introduction

SC1 INVESTIGATION: RATES OF REACTION > Introduction The rate of a reaction is the speed at which a chemical reaction takes place. A chemical reaction is when substances are combined to form new products. Chemical reactions are permanent changes and involve energy to change them In our world, there are millions of chemical reactions happening everywhere. To control the speed of chemical reactions is important, both in our everyday lives and when manufacturing raw materials on an industrial scale, as it helps reduce costs. A few examples of chemical reactions, which take place around us everyday and in factories, are given below: * The burning of petrol in cars. * The browning of an apple which has been bitten. * Respiration taking place in our living cells. * Photosynthesis taking place in green plants (with the aid of sunlight). * The rusting of iron. * Fireworks and other explosions. * Forming plastics from oil. * Producing iron from iron ore. * Making fertilisers from oil and air (the best fertilisers contain ammonium nitrate, made through the Haber Process). Chemical reactions involve bond breaking and forming, which can only occur when reacting particles collide with each other with sufficient energy, in order to form products. Some collisions are successful and give products, whereas others don't because particles do not have sufficient energy to start the process of breaking bonds. Activation energy is the amount of energy needed for the reaction to be started. If there is enough energy, then the reaction takes place and products are formed. But if there is not enough, then no reaction can take place. There are different ways of measuring the rate of reactions. The speed of a reaction can be observed either by how quickly the reactants are used up or how quickly the products are formed. The methods are the following: * If a gas is produced, you can measure the amount of gas released by using a gas syringe to measure the volume of gas given off. ...read more.

Middle

I repeated this three times in total as well. * Finally, I did my last experiment for that variable, by using 0.5 Molar acid. Like the other experiments, I repeated it three times in total and got an average. * While carrying out all of my experiments, I kept the amount of marble chips the same, which was 5 grams. * I recorded the results in a table. Variable = Surface area. * Firstly, I set up the apparatus. * I measured out 50ml of hydrochloric acid, which was 1 molar, in a measuring cylinder and then poured it into the conical flask. * Then I measured 5 grams of powdered marble. * I filled the large bowl with water and then put the measuring cylinder in the bowl. * I turned the measuring cylinder upside down on the beehive shell, so that it was filled with water and has no air in it. * I put one end of the delivery tube in the bung and the other end inside the measuring cylinder via the beehive shell. * I set my stopwatch. * Next, I quickly dropped the powdered marble into the acid, and pushed on the bung. * I then started the stopwatch. This was all done in a very short space of time and I asked some friends to help me, as I would not be able to do all that by myself. * From there, I took the readings of how much time was needed to produce 5ml of gas in the measuring cylinder at a constant rate. I stopped the time as soon as 25ml of gas was produced. * I repeated this experiment three times in total to give me an average. * After that, I carried out the same experiment but changed the surface area to small marble chips. I repeated this three times in total as well. ...read more.

Conclusion

I think this is the reason for the anomalous result, which I got, as I think I did not start the stopwatch at the correct time as I put the bung on top of the conical flask. I could have improved my experiment by using more accurate equipment. For example, a more accurate measuring cylinder to record reliable results, or an even harder task would be to try and work out the total surface area for each of the tests. I could also have used a gas syringe to measure the amount of gas given off, to give me more accurate results. Also, I could have carried on with my experiment for a longer period and not have just stopped when 25ml of gas was produced. This may have changed the shape of my graph and could have made my results more reliable. I could have used two different methods for my experiment. This would have given me two sets of results . This could have given me a firmer conclusion. To provide more evidence for my investigation, I could use a thermometer to measure the temperature during the experiment. I think this would make my experiment more accurate and would give me precise results. For further investigation, I could use a stronger acid to see if there is a limit to how quickly the reaction can take place. Also, I could measure and record the mass loss of the reaction by having the conical flask on a top pan balance. I could take away the mass at regular intervals from the original mass and find out how quickly the reaction takes place. I could look closely at the temperature change and measure that. I could also have watch the solution turn cloudy as the reaction took place. I could have record how long it takes for it to go completely cloudy. If the reactants were of different colours, then I could have measured the colour change. I could also see what would happen if a catalyst was added. BY RAJIV PATEL 11/6. ...read more.

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