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the Determination of a Rate Equation

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Introduction

THE DETERMINATION OF A RATE EQUATION Rate equation has the form rate = k [A]x[B]y which shows how the rate of a chemical reaction depends on the concentration of the reactants (A&B) and the rate constant k. The rate equation normally indicates what species are involved in the rate-determining step and how many species are involved. A rate equation is used to describe how the concentration of a product increases or the concentration of the reactants decreases with time, the equation also indicates how the concentration of one or more reactants directly affects the rate. Occasionally it can even be the concentration of a product that affects the rate. In general the rate equation for the reaction: A + B C + D Is found by experiment to follow simple kinetics with the rate equation being written as: Rate = k [A]x[B]y k = rate constant, x = order with respect to [A], y = order with respect with [B]. There are three orders of reactions, zero order, first order and second order. Zero order = the rate does not depend upon the concentration of the reactant. The rate of reaction is fixed. ...read more.

Middle

* At this point get your stopwatch ready. * Then pick up the beaker with the corresponding concentration to the one on the conical flask. * Pour this into the conical flask, and as soon as the first drop hits the Na2S2O3 start the stopwatch. * When the cross is no longer visible through the solution stop the stopwatch and record the time in seconds. * Repeat this for all the different concentrations. * The experiment must be done away from sunlight as this can affect the temperature of the solution-causing there to be an increase in rate. The experiment must also be done on the same day, as there may be climate changes on different days. * Goggles must be worn throughout the experiment as acid is involved. METHOD 2 * Follow the same method as method 1, but instead using the dilution table for Na2S2O3 and keeping HCl constant by measuring out 10cm3 of HCl into each conical flask using a burette. SAFETY * Goggles must be worn throughout the experiment. * Long hair must be tied back. * Gloves should be worn, if necessary. RESULTS TABLE Concentration of HCl (Mol dm-3) ...read more.

Conclusion

My results were very similar for my repeated experiment but to get more accurate results I could have repeated it more than twice. When pouring the solution into the conical flask to start the reaction not all the solution would go into the conical flask some is always left behind this could have also affected the results as not the exact amount of the solution is reacting that should have. To improve this I would suggest rinsing out with distilled water but this in turn would mean that the concentration would be altered so this wouldn't work. Also when doing the experiment the temperature was not always constant in the surroundings and in the solution. This could have affected the rate of reaction by some reactions happening faster and some slower than the others. To improve this i could make sure all the solutions were at the same temperature before starting the reaction. This would then ensure that the test was being conducted fairly and that way i could get more accurate results. To improve the experiment and minimise errors I can try and devise a better method that would ensure that all of the above errors were reduced. When measuring out my solutions I was taking readings from below the meniscus, this reduced the numbers of errors in my results. ...read more.

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