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Investigation Into the Factors Affecting Rate of Reaction

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Introduction

Chemistry Coursework: Rates of Reaction Prediction I have chosen to base my coursework upon rates of reaction. The rate of a reaction is the speed in which a chemical reaction occurs. Concentration is my main focus within rates of reaction as I aim to find out how the different concentrations effect how slowly or quickly a reaction takes place. The chemicals I will be using for this experiment are hydrochloric Acid and Sodium Thiosulphate. These two chemicals react within a certain length of time depending on factors like concentration and temperature; therefore I can measure the length of the reaction. The balanced symbol and word equation for this is: 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + SO2(g) + H2O(aq) + S(s) Hydrochloric Acid + Sodium Thiosulphate Sodium Chloride + Sulphur Dioxide + Water + Sulphur To attempt this method, I will need to devise a way to make separate concentrations of hydrochloric acid. I will keep all the concentrations for the other chemicals the same. To do this I shall have to use the formulae: C = C1=Original acid concentration V1=Original volume of acid added V2=Total Volume of acid + water The concentrations will look like this: Hydrochloric Sodium Distilled Water Concentration Acid Thiosulphate (Cm3) (Cm3) (Cm�) (Molar) 20.00 20.00 0.00 2.00 17.50 20.00 2.50 1.75 15.00 20.00 5.00 1.50 12.50 20.00 7.50 1.25 10.00 20.00 10.00 1.00 7.50 20.00 12.50 0.75 5.00 20.00 15.00 0.50 2.50 20.00 17.50 0.25 I will choose 8 different concentrations which range from 2 molars to 0.25 molars. I will decrease by 0.25 molars each time. This will give me an accurate idea of how concentration affects rates of reaction. I will mix each concentration with the same amount and concentration of Sodium Thiosulphate and observe the time it takes for the solution to become an opaque yellow colour due to the sulphur produced as a product of the reaction. ...read more.

Middle

This is only a difference of about 7 seconds, which is not what I had expected. I would have thought that there would have been at least a 60 second difference because there was much less concentrated acid placed into the second flasks. The collision theory states that as the particles of acid are reduced, there will be fewer reactions per second and therefore a longer time. The results I obtained may have come up because through chance, more particles were colliding and with the correct orientation. This may lead to a closer result. In table form, the preliminary results looked like the following: Concentration/Molars Time Taken/Seconds Start Temperature/?C End Temperature/?C 2 12.56 22 21 0.25 17.34 22 21 Concentration/Molars Time Taken/Seconds Start Temperature/?C End Temperature/?C 2 11.21 22 21 0.25 18.12 22 21 Concentration/Molars Time Taken/Seconds Start Temperature/?C End Temperature/?C 2 12.58 22 21 0.25 19.63 22 21 The temperatures I took for the experiments showed that there was a change by 1 degree. This meant that the temperature went down, instead of going up, as I had expected. This shows that the solution was cooling as the reaction progressed. This is unexpected because usually when a reaction such as this happens; the energy produced causes heat and not cools the surroundings. I say this because the collision theory states that when two particles hit each other, they release energy in the form of heat. This may not have been the case in my preliminary investigation because perhaps the atmospheric temperature changed slightly whilst I was doing the experiments, which may have lead to the fluctuations in my data. Another factor could have been the temperature of the distilled water of hydrochloric acid that I added to the sodium thiosulphate. Method 1. Collect equipment and lay out on desk. 2. Fill a conical flask with 20ml of sodium thiosulphate using the burettes. 3. Using a piece of plain paper and a permanent marker, draw out a cross or use a cross provided. 4. ...read more.

Conclusion

This will also ensure that the residue on the conical flask after the experiment is finished will not affect my view of the solution. The final improvement I could have made is to include many more concentrations and possibly use hydrochloric acid that was more than 2 molars. This would give me much more variety to work with. To extend the experiment even further, I would try to change the temperature of the solution so that I could see the effect of a higher or lower temperature of the solution. This would give me quite a broad set of results to analyze. In order to accomplish this, I would have to use water baths that contained water at different temperatures. I would probably use ten water baths with temperatures ranging from 0 degrees centigrade up to 90 degrees centigrade. I would only use one concentration or if I had a great deal of time, I could use these temperatures for every concentration. I would expect that if I did this experiment, the lowest temperature water bath would produce the slowest reaction time and the highest temperature water bath to produce the quickest reaction time. This is because there would be more energy in a hotter environment for the particles to move around in, which would stimulate many more successful collisions per second, therefore speeding up the reaction time. A cooler environment would slow the reaction time because there would be less energy for the particles to move around in. I would expect the graph of that experiment to look something like this: This graph shows that as the temperature increases, the time taken for the reaction to happen will decrease. This is true because the collision theory states that more energy produces more collisions per second and heat is energy. In a lower temperature, there is less energy therefore the reactions are much slower. ?? ?? ?? ?? Benjamin Banurji Chemistry Coursework Mr Graham ...read more.

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