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Factors affecting reaction speed

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Introduction

Title: Factors affecting reaction speed. Research Question: To explore how temperature and concentration of reactants affect reaction speed of the reaction speed between sodium thiosulphate and hydrochloric acid? Background Information: As the temperature of the reactants increases the reaction speed will increase. According to the collision theory, when two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place. The two molecules will only react if they have enough energy. By heating the mixture, you will raise the energy levels of the molecules involved in the reaction. According to the kinetic theory, increasing temperature means the molecules move faster. However, the main reason why it increases the rate of reaction is that more of the colliding particles will have the necessary activation energy resulting in more successful collisions According to the collision theory, increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. When collisions occur, they do not always result in a reaction, this is because the molecules in the reaction mixture have a range of energy levels. If the two colliding molecules have sufficient energy they will react. The rate of reaction is limited by the concentration of the weaker solution, and increasing the concentration of the other makes no difference. ...read more.

Middle

Record the temperature inside the water bath. 14. Add the reactants and record the time it takes for the "X" to disappear from view. 15. Use the cold water bath to do it one more time at an even lower temperature by repeating the steps 13 and 14. 16. Use another water bath, but fill it with hot water. 17. Record the temperature inside the water bath. 18. Add 10cm3 of sodium thiosulphate and 10cm3 of hydrochloric acid. 19. Start the stopwatch as soon as the reaction begins and gently stir. Stop it when the "X" disappears from view. Record this time. 20. Use the hot water bath again at another high temperature. 21. Repeat steps 17, 18, and 19. Data Collection: Changes in concentration of reactants Sodium Thiosulphate (cm3) ?0.05cm3 Water (cm3) �0.05cm3 Hydrochloric Acid (cm3) ?0.05cm3 Time Taken t (seconds) Reaction speed (1/t) (per second) 25 0 10 95.03 0.0105 20 5 10 103.35 0.0097 15 10 10 108.57 0.0092 10 15 10 114.28 0.0088 5 20 10 118.31 0.0085 Changes in temperature Temperature (�C) ?0.5�C Time Taken t (seconds) Reaction speed (1/t) (per second) Room Temperature - 26 84.78 0.0118 Ice Water Bath - 18 88.28 0.0113 Ice Water Bath - 9 99.78 0.0100 Hot Water Bath - 63 14.97 0.0668 Hot Water Bath - 50 17.82 0.0561 There was an uncertainty of ?0.05cm3 whenever the volume of the reactants was measured. ...read more.

Conclusion

This increases the probability of a collision between molecules since molecules are moving faster and also since the kinetic energy is high, they are likely to attain the necessary activation energy for the reaction to take place. Evaluation: The hypothesis was supported but there were a few experimental errors that occurred. The measurement of time was not completely accurate since the stopwatch was not started when the reaction actually began and also it was not stopped at the exact moment when the "X" disappeared from view. Another error was from the uncertainties in the equipment we used. There was an uncertainty of ?0.05cm3 when measuring the volume of hydrochloric acid and sodium thiosulphate. When mixing water and sodium thiosulphate this increased to ?0.10cm3. Also the measurement of temperature with the thermometer had an uncertainty of ?0.5�C. Since this was an experiment based on the judgement of the eye with regards to when the "X" actually disappeared, sometimes it may not correct because we may stop the time even though the "X" is still visible. There were changes in temperature while doing the experiment since this was not done in vacuum and outside conditions may have affected the results. Next time, to make this experiment better we can do it in vacuum and under a controlled environment where temperature and pressure are constant. ?? ?? ?? ?? Reaction Speed Lab 13th March 2007 Page 1 of 6 ...read more.

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