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Rates of Reaction.

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Introduction

Rates of Reaction The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by the time taken of the reaction�1. The speed of a reaction can be increased by: 1. Raising the Temperature 2. Adding a Catalyst 3. Increasing the concentration 4. Increasing the Pressure (gases) 5. Increasing Surface Area All of these raise the speed of reaction because of the particle collision theory. Particle Collision Theory For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area. See bibliography for where I obtained my information. 1. When the temperature of the reacting substances is increased, the particles move quicker. As the particles are moving quickly, the particles are going to have more collisions. As the particles also have more energy, they will collide with more energy. ...read more.

Middle

6. Record selected temperature and time taken for reaction to occur. 7. Wash out conical flask. 8. Repeat steps 1-7 for three more different temperatures Pre-test Results Table Temp Time Taken (s) 17�C 60 19�C 57 28�C 35 80�C 10 Prediction I have chosen a range of temperatures between 80�C and 15� to test for the smallest rate of reaction. The reaction between Sodium Thiosulphate and Hydrochloric Acid produces Sulphur precipitate. This makes the solution of Sodium Thiosulphate and Hydrochloric Acid turn cloudy. I predict that the experiment carried out at the temperature closest to 80�C will take place in the smallest amount of time to complete because of things I have found out about the Particle Collision Theory. I have found out that when the temperatures of one or both of the reactants are raised the particles will move faster as they have more energy to move around. As the particles are moving around faster there will be more collisions between the particles. I predict that my results will rise proportionally. When the temperature is increased by 10�C the rate of reaction doubles, thus the time taken for the reaction to take place will halve. I have also found that there is a minimum amount of energy that the reacting particles need to collide with each other so that they do react. This minimum energy is called the activation energy. From this information I have reached a conclusion that heating the particles will give them more energy. ...read more.

Conclusion

However this is the not the case. The actual time taken is 34 seconds. This shows that there were some anomalies in my results. Still, my results are fairly accurate as my graph is true to the graph you would expect to get from a perfect set of results. Evaluation Overall, I think the experiment went quite well. Although I have a set of results that are slightly inaccurate, they are still accurate enough for me to give a firm conclusion. My results support my prediction and I think I used a significant range of temperatures and repetitions to give a firm set of results. As I used the same equipment through out the experiment any errors due to the equipment I used can be eliminated. The only error that cannot be eliminated is when I judged whether or not I could see the cross through the solution. This cannot be eliminated because although I could not see the cross anymore, some of the reactions could have been further on than others carried out at the same temperature even if they had been ongoing for only a few seconds, or even a hundredth of a second, more or less than each other. Also I may have been able to get more accurate results by using light detectors which record the amount of light that passes through the solution and then displays the results (in real time) on a graph on a computer. By using these light detectors, instead of when a cross can no longer be seen through the solution, my results would be more accurate. ...read more.

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