I aim to investigate the affect of temperature on the rate of reaction between sodium thiosulphate and hydrochloric acid.

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GCSE Coursework: Chemistry

Planning

I aim to investigate the affect of temperature on the rate of reaction between sodium thiosulphate and hydrochloric acid;

Sodium thiosulphate + hydrochloric acid → sodium chloride + water + sulphur dioxide + sulphur

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l)+ SO2(aq) + S(s)

The input variables which might affect the outcome if the investigation are the concentration levels and temperature, whilst only investigating the temperature and keeping the concentration levels the same.

The output variables I intend to measure are time (s), and the rate of reaction, 1/time (s-1). I will measure the output variables with a stopwatch, timing to see how long it takes for the solution to turn cloudy.

I predict that the higher the temperature, the more quickly reaction will occur. This is because with heat, the particles of sodium thiosulphate and hydrochloric acid have more energy and this obviously causes them to move around more. It works like this for all substances, not just those two though. Chemical reactions require collisions, and if particles are moving around more quickly they are obviously more likely to collide. It is just like in a crowded street. If the people are moving quickly it is more likely that they will bump into each other then if they are moving slowly. The particles of this solution react in more a less the same way.

        I found out from secondary sources such as books that the particle theory explains that chemical reactions require a collision between the particles of the reactants, at a certain velocity (i.e. speed) and angle. If this angle or velocity is not achieved, the substances will not react together. I also found out that there are several other factors that affect the rate of a reaction including the surface area of the solid pieces (if there is a solid), the concentration levels and the presence of catalysts and temperature. In this experiment we are only interested in temperature. Where temperature is not high enough to provide energy for the particles to move at a high enough speed, the particles will just not react. Basically, not as many particles will be able to react together in a certain amount of time.

For 21°C to 41°C, I predict that the rate of reaction will increase considerably after comparing the results for 21°C and 41°C. This is due to the fact that there is more heat to provide energy to the particles of the reactants. This energy causes the particles (sodium thiosulphate and hydrochloric acid) to move around more quickly, and as a consequence more collisions will take place between the particles.

At a temperature of 41°C up to 61°C, I formed the prediction that that the reaction will occur even more quickly than any temperatures between 21°C and 41°C. This is because by this time there is so much heat, which gives the particles of sodium thiosulphate and hydrochloric acid even more energy, allowing them to move around more quickly than before. Obviously, at a higher velocity the particles are going to be more likely to collide. Chemical reactions require collisions, and if the particles are more likely to collide then the reaction will occur faster. Once these temperatures have been reached the rate of reaction will have no doubt decreased even more dramatically than the drop from the rate of reaction for 21°C and 31°C.

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In basic terms, at a cold temperature the reaction will take more time to happen. This is because the particles of sodium thiosulphate and hydrochloric acid will not be moving around so quickly, meaning they are less likely to collide, therefore the reaction will require more time in order to occur. Chemical reactions require a collision at a certain velocity, and if this velocity is not reached then the reaction will simply not happen.

As the temperature increases, the rate of reaction will be lower. This is because with more heat, the particles have more energy, meaning they move around ...

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