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Factors that affect the rate of reaction.

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Factors that affect the rate of reaction Background We can measure the rate of reaction by measuring the rate of change by either, - one of the reactants disappearing with time - one of the product forming with time. A chemical reaction can only occur between particles when they collide (hit each other). Particles may be atoms, ions or molecules. There is a minimum amount of energy which colliding particles need in order to react with each other. If the colliding particles have less then this minimum energy, then they just bounce off each other and no reaction occurs. This minimum is called the minimum energy. Collision Theory: - particles must collide - with sufficient energy to break existing bonds - with the correct orientation Measuring rates: We can measure how quickly products form or we can also measure how quickly reactants are used up. Here are some graphs which you can get whilst studying these two different methods, Factors that affect the rate of reaction: 1.Raising the temperature has the same effect on all three reactions. Raising the temperature makes the particles move faster. This means that more particles collide with each other per second. The rate of the reaction increases. Also, the faster the particles are travelling, the greater is the proportion of them which will have the required minimum energy for reaction to occur. As a general guide, raising the temperature of a reaction by 10 �C will double the rate of the reaction. The gradient of the plot will be twice as steep. Here is a prediction graph for an experiment investigating the effect of temperature on the rate of a reaction: 2.Increasing the concentration (in solution). Increasing the concentration of a substance in solution means that there will be more particles per dm3 of that substance. The more particles that there are, the more will collide per second, and so the rate of the reaction increases. ...read more.


Time taken for cross to disappear (secs) Rate of the reaction (/s) 1 40 32 0.031 1 4 321 0.003 2 40 19 0.053 2 4 242 0.004 0.5 40 40 0.025 0.5 4 773 0.001 Conclusion: I am going to use the 2 Molar acid in my main experiment. This is because it had the fastest results, where as the 0.5 Molar acid had results which took too long (776 secs). If I used this in my final experiment then I would not have enough time to collect sufficient evidence to support my case. Final Experiment Safety: To make sure that I, and people around me are safe whilst I am carrying out my experiment, I will remember the following points, - I will remember to wear goggles to protect my eyes - I will remember to wear a lab coat to protect my clothes and skin - I will tuck my stool out of the way, so no one can trip over it. - I will make sure my bag is tucked away, so no one could trip over it - I will not rush about or run, resulting in knocking something or someone over - I will stand up whilst doing my experiment, so that just in case something spills, I will be able to get away fast - I will not leave the apparatus at the side of the table, so it cannot get knocked over - I will wear my hair up Here is some safety information about hydrochloric acid and sodium thiosulphate which I will be handling during the experiment. Hydrochloric acid: Corrosive: may cause burns. The vapur is very irritating to the respiratory system. Solutions equal to and greater then 6.5 M are corrosive and those equal to and greater than 2 M but less then 6.5 are irritant. It could be deemed sensible to label 1 M solutions as irritant as well. ...read more.


Also, I could of started the stop-clock slightly after or before I actually should of. The information that I collected could be adequate to support my conclusion fully, I could of however collected more evidence by doing more repeats and maybe doing more different molars of acid and concentrations of thiosulphate. By collecting more evidence, I would of had a wider range of information from which to make an average out of. Also I would of repeated all of the anomalies that I acquired, resulting in a more accurate average. If I had, had more time. I do feel that the method that I used was suitable for my experiment. If I could of, I could of used a light sensor and data logging to investigate in more accurate detail. The light sensor detects the amount of light that travels through the reaction mixture in the beaker. As the mixture gets cloudier the amount of light reaching the light sensor decreases. This would of acquired much more accurate results, as it uses digital readings to get the results. To extend my experiment I could of investigated another factor that affects the rate of reaction, for example, the effect of temperature on a reaction rate. Here is the method that I would of followed: - Put 10cm3 of sodium thiosulphate solution and 40cm3 of water into a flask. - Measure out 5cm3 of dilute hydrochloric acid in a small cylinder. - Warm the thiosulphate solution in the flask if necessary, to bring it to the required temperature. (I would do this experiment five times, with temperatures in the range 15-65 degrees Celsius.) - Add the acid from the cylinder and start the clock. Swirl the flask to mix the solutions and place it on a piece of white paper marked with a cross - Look down at the cross from above. When the cross disappears. Stop the clock and note the time taken. Record the temperature of the mixture in the flask. ...read more.

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