Rate Of Reaction

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Science Coursework: Rate Of Reaction

        

Aim:

The rate of reaction can be altered by varying temperature or concentration, or by changing the surface area of a solid reactant, or by adding a catalyst and increasing the pressure.

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I am going to investigate the reaction between hydrochloric acid and sodium Thiosulphate, which is a precipitation reaction, and their rate depends on temperature and the concentrations of the solutions. I will repeat this experiment at several different temperatures and concentrations. I am going to observe how the concentration and temperature will affect the rate of reaction (temperature /average time).Below is the word and symbol equation that they react in.

Sodium Thiosulphate + Hydrochloric acid -> Sodium Chloride + Sulphur + Sulphur Dioxide + Water

Na2S2O3 (aq) + 2HCl (aq) -> 2NaCl (aq) + S (s) + SO2 (g) + H2O (l)

Prediction:

For temperature I have predicted that when the temperature is increased the time and rate are likely to decrease as the reaction will happen faster. I predicted this because of the collision theory, and because I was certain that the higher the temperature would be the faster the particles will moves, therefore they will combine quicker with the other substance which is likely to make the reaction faster. The solid sulphur formed in this reaction makes the colourless solution go cloudy.

Concentration, just as increasing the temperature will increase the number of particles colliding, so will the concentration. This experiment is basically about more particles into the reaction, the probability of the colliding (crashing) is increased so the reaction is bound to take place faster. This variable is continuous and independent. As I mentioned in my aim I will be experimenting on this reaction. I predict that by doubling the concentration of the acid, the rate of reaction will double, however the time will decrease as it is happening faster.

I am going to test the two variables concentration and temperature. Both of these are independent, continuous variables. I think that concentration will have the biggest affect because the reaction is exothermic, this is a reaction where energy is released causing a rise in temperature. Therefore, as I will test concentration heat will probably be given out and this is useful because this will give the particles more energy however this is not going to create an extreme difference. With the help of the equation I also manage to find out, using my mathematical skills, that for every 1 particle (or molecule) of sodium thiosulphate there are 2 moles or hydrochloric acid. This means that increasing the hydrochloric acid will have a greater effect as this will even the molecules up, therefore the molecules of sodium thiosulphate colliding with the hydrochloric acid molecules is very likely.

This diagram explains exothermic mean and show what it would do in a reaction:

Here is a very brief summary of what I have predicted:

Concentration: Doubling the number of particles doubles the probability that they will collide. Therefore they will react quicker, and the rate or reaction will increase.

Temperature: If I double the speed at which doubling at which the particles travel will double the rate of reaction as they can travel faster so it double the probability of them colliding.

I also made predictions for other ways for testing the rate of reaction, these were mentioned in aim.

Surface Area – The larger the surface area, the more particles are exposed and therefore there is a larger area for the particles of the reactants to collide with and as a result of this a reaction will probably take place. This means that the larger the surface area, the faster the rate of reaction as there will be a higher probability of the particles of the reactants (sodium thiosulphate and hydrochloric acid) colliding with each other. I didn’t choose to do this test because this could prove to be difficult as I am dealing with liquids hence it is hard to control the surface area.

 Adding a catalyst – Catalysts are substances which help to speed up chemical reactions without being used up in the reaction themselves, that’s why they are helpful. Even when the reaction is over, the catalyst is technically unchanged. Catalysts work by lowering the activation energy required for the experiment to start. However as I didn’t do this test because adding a catalyst would make things harder or complicated, moreover if I use it improperly then this could end up in inaccurately.  

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Pressure – The higher the pressure, the more collisions occur and so the rate of reaction is greater. This is because the particles are squashed together which results in them colliding more often. I didn’t do this test as this does not apply to my investigation, because in my experiment the reactants are liquid and solid (sulphur) and both of these substances are difficult to compress, unlike gases.

Preliminary test:

By doing a preliminary test I want to find out how I should put the substances in the conical flask and I also need to find out how ...

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