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Investigate and conclude what factors affect the rate of a chemical reaction, and specifically investigating the concentration as a factor.

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Factors affecting the rate of a reaction Aim: To investigate and conclude what factors affect the rate of a chemical reaction, and specifically investigating the concentration as a factor. Introduction: A chemical reaction occurs when two or more reactants combine to form one or more products. Examples of such a reaction include the oxidation of sodium, where sodium reacts with oxygen in the air to form sodium oxide. There are a number of factors, however, which influence the rate at which the reaction occurs. These factors are the temperature, the concentration of the reactants, the surface area of the reactants, and catalysts. In this coursework I will be investigating how the temperature, the concentration of reactants and the surface area of the reactants, affect the rate at which a reaction takes place. Temperature The collision theory states that particles of the reactants must collide, with certain activation energy, in order for the particles to react. However not all of the particles meet this activation energy requirement, and so fail to react. This activation energy requirement varies according to the reaction undergone; however there is a general trend in the activation energy levels for exothermic and endothermic reactions: Endothermic reactions (left): The reactants need the activation energy (Ea) as well as ?H in order for the reaction to commence. Once started however, only the Ea energy is given off, and the products absorb ?H, so that the products contain more energy than the reactants. Exothermic reactions (right): The reactants need the activation energy (Ea) in order for the reaction to commence. Once started however, Ea and ?H energy is released, so that the products contain less energy than the reactants. Only a fraction of the total number of collisions per second are successful, and the rate at which the reaction commences is directly proportional to the collisions frequency. The kinetic theory states that the more thermal (kinetic) ...read more.


From the working above, it has become evident that I will be using 0.00192 moles of Magnesium in my reactions. Therefore, an equal number of moles of Hydrogen gas will also be produced; therefore, 0.00192 moles of Hydrogen gas will be produced in the reaction. "For reactions involving gases reacting (and any gaseous products that form), it was observed that they do so in volumes which are in ratios of small whole numbers, when measured under the same conditions of temperature and pressure. This is expressed as Gay-Lussac's Law (1808). This observation was explained by Avogadro, and is expressed as Avogadro's Law (1811). Equal volumes of any gases measured under the same conditions of temperature and pressure contain equal numbers of molecules (or atoms if the gas in monatomic)." Secondary Source: Britannica Online The Molar Volume is the volume of 1 mole of a gas. This, of course, depends upon the temperature and pressure at which it is measured. The Molar Volume at room temperature and pressure (298 K, 1 atm.) is 24 dm3. From this, I can work out, in theory, how much Hydrogen gas will be produced from the reaction. The formula for finding out the volume occupied by a gas at room temperature and pressure is as follows: Moles of Hydrogen gas produced= 0.00192 (3 S.F.) Volume of gas taken by 1 mole of gas atoms or molecules = 24 dm3 Therefore, Volume= 0.00192 * 24000 cm3 = 46.1cm3 (3 S.F.) I know, therefore, that I will be expecting to obtain a volume of roughly around 46cm3 of Hydrogen gas (H2) from each of the different concentration reactions. Preliminary Experiment I tested my theory at home. I got two "Rennie" tablets and placed one in a cup of lemon juice, and the other in a cup of diluted lemon juice, thus creating an independent concentration variable. The tablet reacted faster in the cup of concentrated lemon juice, rather than the diluted one. ...read more.


The results obtained from my preliminary test also confirm the accuracy of the results obtained in this investigation, as well as support my prediction. Concentration of HCl acid 2.0 Molar 1.75 Molar 1.50 Molar 1.25 Molar 1.0 Molar Average Volume (cm�) of Hydrogen Produced 49.8 46.7 42.3 41 48.8 45.7 (3.S.F.) The table above gives the volume of Hydrogen gas collected from each of the different concentration of HCL acid. It can be seen that the average result of 45.7cm� Hydrogen gas is very close to the predicted volume of gas via using quantitative chemistry (46cm�), and therefore goes to show that the experiments were done very accurately indeed. Evaluation The investigation went quite successfully, with some very good results obtained. These results I found were quite sufficient to base a firm conclusion on. The results were sequenced, with a visible trend displayed on the graphs. There was a little percentage error, and no substantial anomalous results were obtained. The repeated measurements increased the overall accuracy of the results and the general procedure used was quite good, enabling the output of quite accurate results. Nonetheless, various steps could be made to the procedure to ensure the results obtained would be even more accurate. I suggest using a computerised data logging set of apparatus where the exact starting masses can be recorded by the computer. Also, graphs of the reaction rate would be automatically created, and these could aid me further in my conclusions. It would also be interesting to investigate how other factors affect the rate at which the reaction occurs. Such factors could include the effect of catalysts on the rate of the reaction, as well as the effect of the pH on the rate at which a reaction occurs. These are in addition to all the other factors I listed in my introduction, in which I would like to test them out to see if they correspond to the theory and the preliminary experiments I did for each of them. Maytham Aomran GCSE Chemistry Coursework - Page 1 of 19 - ...read more.

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