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Rates of Reaction

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Introduction

Rates of Reaction AIM In all chemical reactions products are formed and reactants are used up. The following are factors, which affect the rate of reaction: * Surface area of solid reactants. * Changes in concentration of solution in which reactant is placed. * Changes in Pressure (if reactant is gas). * Changes in Temperature. * Catalysts. I will be investigating the affect concentration has on the rate of reaction between Magnesium and Hydrochloric Acid. The reactants in this investigation are the magnesium ribbon and the hydrochloric acid. The products are Magnesium Chloride and Hydrogen (gas). The following equation demonstrates this: Mg(S) + 2HCl(AQ) MgCl2(AQ) + H2(G) Magnesium + Hydrochloric Acid Magnesium Chloride + Hydrogen I must remember that most of the factors listed above will in some way affect the rate of reaction i.e. the Surface area of the Magnesium ribbon, the temperature of the Hydrochloric Acid. PREDICTION From previous experiments I have discovered that the rate of reaction is directly proportional to the concentration. When Dilute Hydrochloric acid and sodium thiosulphate react, the higher the concentration the faster they react. I also noticed that as the concentration doubled the rate also doubled. I predict that as the concentration of Hydrochloric acid doubles the rate of reaction will also double. SCIENTIFIC KNOWLEDGE For all Chemical reactions there is a rearrangement of atoms. We can see this by looking at a simpler chemical reaction like the production of Water (H2O). + Hydrogen Oxygen Water Molecules molecule Molecule In order to form Water the Hydrogen and oxygen molecules must collide! Particles in liquids are in constant motion (Kinetic theory). Kinetic theory derived from the concept of Brownian motion discovered by a botanist called Robert Brown in 1827. He discovered that tiny molecules in a liquid or a gas would make suspended particles move when they collided. From this we can make judgements. In order for the larger particles to move the molecules in the liquid must have been moving at a relatively fast speed. ...read more.

Middle

As soon as the lid is on start the timer. * Make sure exactly 25cm� of H2 has been collected and then stop the timer. * *To find the average, we will calculate the sum of the 3 times for each concentration, we will then divide this sum by 3. This is done so the results will be more reliable. * I will record time in seconds and to one decimal space, for accuracy. * I will repeat any results, which seem anomalous. SAFETY PRECAUTIONS I must give a lot of consideration to the safety aspects of this investigation for the sake of fellow students and myself: * As I will be handling HCl, which is an irritant, I must have eye protection and when handling the more concentrated solutions should have some kind of skin protection. I must generally be careful when handling the acid. * As I will be using a lot of glass apparatus which is sharp when broken I must be aware of this during the experiment and when putting all the apparatus back. * I must take care when it comes to the disposal of chemicals. RESULTS The following table contains the time taken to collect 25cm� for all three experiments and the average time for each concentration has been calculated. Concentration of HCL (M) Experiment 1 (Seconds) Experiment 2 (Seconds) Experiment 3 (Seconds) Average Time (seconds) 2 4.4 5.3 5.1 4.9 1.8 5.9 6.2 7.1 6.4 1.6 7.8 8.1 8.3 8.0 1.4 10.5 11.2 11.1 10.9 1.2 15 14.7 14.8 14.8 1 23.5 23.5 22 23 0.8 40.6 78.6 38.9 52.7 0.6 63.2 367 243 224.4 After observing the results I gained from the experiment, I can see some results, which seem anomalous, they will affect the shape of the curve and thus I will not be able to make accurate observations. The figures in the table above, which have been highlighted red are the ones which I don't think are correct. ...read more.

Conclusion

* The reaction between Magnesium and HCl is an exothermic reaction. Heat is spread to the surroundings. Thus, raising the temperature of the solution, this adds to the rate of reaction. The following are improvements I would make for any further investigation: * Use Magnesium filings, as the impact of H2 molecules on the surface would not be as much as Magnesium ribbon. * Take a lot more care when measuring all solutions. * Making sure the containers are always dry on the inside. * When measuring out concentrations I should double check whether the right amounts of HCL and water have been added together. * I could use a gas syringe to collect the gas this would be more reliable than the displacement of water and their would be less faults in the timing of when 25cm� of H2 is collected. * I could use computers to construct graphs, which would give me more accurate best-fit lines, which I could read of. To improve my investigation I can take other factors into account and observe how they would affect the rate of reaction, the following factors are worth considering: * Surface area - If I were to carry out such experiment I would predict that as the surface area of the Magnesium increased, there would be a higher rate of 'successful' collisions, which would increase the rate of reaction. * Temperature - I would predict that as the temperature increased the rate of reaction would increase. The higher temperature provides the particles with higher energy levels so more particles posses' energy greater than the Activation Energy (Ea) so collide 'successfully'. * Use of a catalyst- a catalyst can alter the rate of reaction be reducing or increasing the Activation Energy (Ea) for a particular reaction. If a Catalyst, which reduces the Activation Energy (Ea) for particles in the reaction between Magnesium and Hydrochloric Acid. This would result in a higher proportion of 'successful' collisions. Thus increasing the rate of reaction. Maryam Shah 17637/8503 ...read more.

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