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To investigate how particle size affects reaction rates

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Introduction

Chemistry Coursework Purpose : To investigate how particle size affects reaction rates Key factors > Temperature > Particle size > Concentration > Measurements > Pressure > Catalysts Background information A chemical reaction involves one or more substances (reactants) that react to produce other substances (products). Chemical engineers exploit chemical reactions to produce materials on a commercial scale. Different reactions happen at different speeds (rates.) Some reactions like explosives are so fast they are almost instantaneous. For example, when a burning splint is put into a mixture of hydrogen and chlorine, there is a loud bang and hydrogen is produced: H2 (g) + CL2 (g) ? 2HCL (g) Other reactions, like the rusting of steel and the weathering of limestone on buildings happens so slowly that it may be years or even centuries before we notice their effects. The following is the way to work out the reaction rate: Reaction rate = Change in amount (or concentration) of a substance Time taken E.g. 0.1g of magnesium added to dilute hydrochloric acid disappears in 10 seconds Rate = 0.1 10 = 0.01g/s "The speed of a reaction is inversely proportional to the time taken for the reaction to finish" The rate of reactions can be measured in two different ways: > Measuring change in mass on scales > Measuring gas produced with a gas cylinder Both are equally good measures of the rate of reaction. To measure change in mass is relatively easy; you just add the reactants together and measure the change in mass. ...read more.

Middle

For the same mass, small chips can have a several times larger surface area. This therefore speeds up the rate of reaction as the reactive substance (hydro choleric acid) can be dissolving many different sides of the chips at any one time rather than having to dissolve a whole side before reaching the next bit. The diagram below shows the acid (arrows) and the chips (square) the whole one has been divided up in to segments to illustrate the area that is left unexposed as compared to the small chips. "Reactions in which the reactant is solid take place faster when the solid is divided into small pieces. The smaller particle have a large surface area to mass ratio against the larger particles" --------------- A reaction into the effects of heat on a reaction (Sodium thio sulphate and hydrochloric acid) Sodium thio sulphate and hydrochloric acid were reacted together at temperature intervals of 10?C. They produced sulphur. Warming the solution makes the sulphur form faster. There is a steep increase in the speed of the reaction as the temperature is increased. The reaction goes approximately twice as fast at 30?C as it does at 20?C. It double speed again between 30?C and 40?C and so on. The reason: At higher temperature the ions have more kinetic energy. Moving through the solution more rapidly, they collide more often and so there is a greater chance they will react each second. Therefore the reaction will finish much quicker. Safety To ensure safety, I must follow several rules when conducting my experiment. ...read more.

Conclusion

Explaination Evaluation The experiment was very successful and I would say that there do not seem to be any major inaccuracies. The result for 15 marble chips is slightly lower than anticipated but still reasonable. The results are accurate as we repeated the experiment three times and then took an average. Certainty & Experimental Error As with any experiment that is not done in a completely scientific laboratory with perfect equipment, there will be small inaccuracies that, although you may try to avoid will still be there. The actual markings on the gas syringe that we took the measurements fast cannot be 100% accurate, also we may have read the syringe slightly wrong, resulting in small inaccuracies that could affect the results. The syringe may, itself not be air tight, resulting in small amounts of gas leaking. The bung that connected the gas syringe to the conical flask may have leaked slightly, or some gas may have escaped immediately after we put the marble chips in. We did try to use all the same acid, however some may have been slightly stronger, as we did not measure the strength of each acid we used. Extension We could extend the experiment in several ways; in fact you could carry on extending it almost indefinitely. It would be a sensible start to decrease the amount of time that the samples are taken at. For example take readings every 5 seconds instead of every 10, which would give us a better picture of how the initial rate actually occurs. We could investigate how other reactants occur with marble chips and compare this to our experiment. 1 Reaction Rates Page Steve Green ...read more.

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