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Rates of Reaction.

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Preliminary Research and Background Knowledge The rate of reaction is the change in the concentration of a reactant or product per unit time. We can measure the rate of reaction by timing how quickly the products are made. Also if you know the activation energy required for a reaction to take place, it will help in industry as they can see when how much energy is required for them to add to the reactants to produce the final product quickly. As far as I know, when you react sodium thiosulphate solution with hydrochloric acid you should obtain: - Sodium Thiosulphate + Hydrochloric AcidSodium Chloride + Water + Sulphur Dioxide + Sulphur Na2S2O3 (aq) + 2HCl (aq) 2NaCl (aq) + H2O (l) + SO2 (g) + S (s) Usually only a small percentage of the substances interacting have the minimum amount of kinetic energy a molecule must possess for it to react. When the reactants collide, they may form an intermediate product whose chemical energy is higher than the combined chemical energy of the reactants. In order for this transition state in the reaction to be achieved, some energy must enter into the reaction other than the chemical energy of the reactants. This energy is the activation energy. There is an energy barrier that separates the energy levels of the reactants and products. Energy must be added to the reactants to overcome the energy barrier, which is recovered when products are formed. The energy barrier is known as Ea, the activation energy. The activation energy is distinct from the DG, or free energy difference between the reactants and products. ...read more.


Diagram Apparatus > 750 cm3 of Sodium Thiosulphate Solution > 600 cm3 of Water > 150 cm3 of Hydrochloric Acid > A Conical Flask > 2 Measuring Cylinders (that measure accurately to 1cm3) > A Stopwatch (accurate to 1/100th of a second) > A Piece of Paper and a Pen (the paper is where a large 'X' is drawn on) Safety Points > Make sure that you are wearing goggles to protect your eyes from accidental spills or splashes while making concentrations > Make sure that you also wear a lab coat to prevent acid for getting on your clothes or from reacting with your skin > The reaction between sodium thiosulphate and hydrochloric acid gives off sulphur gas which is poisonous, so after each reaction has finished quickly dispose of the conical flask's contents down a sink and thoroughly clean the flask with water before starting another reaction Method 1. Gather and set up the equipment as shown in the above diagram 2. On the piece of paper mark a large, bold 'X' on it so that when the conical flask is placed on top of it the 'X' can still just be seen around the sides 3. Pick up the two measuring cylinders. In one measuring cylinder, pour out 5cm3 of hydrochloric acid 4. Pour 50cm3 of sodium thiosulphate solution into the conical flask 5. Pour the 5cm3 of hydrochloric acid into the conical flask as well 6. As soon as it is in start timing the reaction with a stopwatch 7. ...read more.


I could have improved my results by adopting the following measures:- > The measurement of volume of acid can be done accurately by drawing the measuring cylinder before use and also by using a white paper to place behind the cylinder to see the exact position of the miniscus > The volume of water which was added each time to the thiosulphate solution could have also been measured more accurately by using more accurately marked cylinders that are easy to read off > The result could also be improved by focussing my eyes constantly on the process of disappearance of 'X'. There should be no need to divert my attention from left to right even once The results can be more accurately judged by using different volumes of water and sodium thiosulphate solution, for example, 2, 4, 6, 8 cm3 of water instead of 5, 10, 15, 20cm3. The results expected should still have the same pattern if the same concentrations of sodium thiosulphate solution are used. This will give us another set of readings of which more graphs can be drawn to investigate the rate of reaction. As for further experiments, the rate of reaction in this case can also be studied by changing the concentration of acid or even by keeping both concentrations the same but by changing the temperature each time. It can be investigated how this would affect the rate of the reaction. I would also have liked to continue the investigation on concentration below 4gpl and see what exactly would happen to the results if they were drawn on a graph. Khushpal Grewal 11K - Page 1 - ...read more.

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