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# An investigation into the effect of concentration on the rate of reaction. The disappearing cross experiment.

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Introduction

Richard Tandy March 2004 Year 11 Science Coursework An investigation into the effect of concentration on the rate of reaction. The disappearing cross experiment. Introduction The rate of reaction is a measure of the change, which happens during a reaction in a single unit of time. There are numerous variables that are specifically known to affect the rate of reaction, the most commonly known being: * Temperature - Temperature alters the rate of a reaction by supplying the reactant particles with more energy, the more energy the reactants have the faster they move around increasing their chance of bumping into one another and having a successful collision. Also the more energy they get from the heat the more particles have enough energy to react, this is known as activation energy. * The surface area (of solids) is another variable that affects the rate of reaction. For example a larger surface area will result in more collisions between the particles and the solids and so this will release more energy and speed up the rate of reaction. * Pressure (in gases) - If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and the likelihood of collisions and thus the rate of reaction. * A Catalyst - A catalyst is a substance that changes the rate of a chemical reaction by providing a lower activation energy but remains chemically unchanged itself. Another variable that affects the rate of a chemical reaction is the concentration (i.e. how close together the particles are in a solution). In this piece of coursework I will be investigating how the concentration will affect the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. I have chosen to investigate the concentration variable, as it is the most practical and straightforward for my experiment. The equation to this reaction is as follows: Sodium + Hydrochloric = Sodium Chloride + Sulphur Dioxide + Sulphur + Water Thiosulphate Acid The symbol equivalent to this equation is as follows: Na2S2O3 (aq) ...read more.

Middle

* The experiment should take place on a flat, level and stable surface, like a table, to prevent spillages. * Make sure equipment is not damaged or broken. Collecting results and starting the experiment I am now ready to undertake my experiment. I will record my results from my experiment in a results table, the same as the one in my preliminary test but a larger version because I only took a few concentrations for my preliminary test. In the results table I will record the data from the chosen concentrations of hydrochloric acid (10 different concentrations ranging from 0.1 molars to 1.0 molars). I will repeat the test for each concentration three times and then find an average rate of reaction time for each concentration - this should provide me with more accurate and reliable results. I will then illustrate my results in my results table by plotting them on a concentration and rate of reaction graph. The results table and my concentration and rate of reaction graph are both on separate pages. Analysis and conclusion From my results I have discovered that as you increase the concentration of the hydrochloric acid solution, the faster the rate of reaction is. This means that the precipitate will form quicker if there is a higher concentration and so the cross will disappear faster. Also the same is true for the opposite, as you decrease the concentration of hydrochloric acid, the slower the rate of reaction is, in other words the lower the concentration of the hydrochloric acid, the longer it takes for the precipitation to form and the cross to disappear. Therefore, after performing my experiment a conclusion can be drawn which states that, if the concentration in a reaction is increased, the rate of reaction will increase, resulting in the fact that the more concentrated the solution, the faster the rate of reaction. This is illustrated in my results table and also on my concentration and rate of reaction graph, which illustrates that as ...read more.

Conclusion

I think this because the temperature alters the rate of a reaction by supplying the reactant particles with more energy, the more energy the reactants have the faster they move around increasing their chance of bumping into one another and having a successful collision. Also the more energy they get from the heat the more particles have enough energy to react, this is known as activation energy. " Surface area (of solids): I think that if the surface area (of solids) is increased the rate of reaction will increase. This is because a larger surface area will increase the probability and will result in more collisions between the particles and the solids and so this will release more energy and increase the rate of reaction. "Pressure (in gasses): I think that if the pressure was increased the rate of reaction would increase. This is because if the pressure is increased the particles in the gas are pushed closer. This increases the concentration and the likelihood of collisions and thus the rate of reaction. "Catalyst: Catalysts increase the rate of reaction without themselves being used up or chemically changed. Catalysts work by lowering the activation energy barrier, this means more reactants can begin to react sooner to turn into the products. An example of a catalyst is manganese dioxide powder; this speeds up the breakdown of hydrogen peroxide into water and oxygen. There are also a number of things that I could do to improve my results or even provide myself with a new, more accurate set of results. As I said, I could have used a light sensor, which would have given me more accurate and precise results as this may be more accurate than my own assessment of the cross disappearing. The other thing I could have also done was to carry out the experiment more than three times. For example, I could have performed it five times in order to get more reliable averages. 1 ...read more.

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