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Investigate the factors affecting the rate of a reaction.

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Rates of Reaction. Max Carter 11EB. Aim: To investigate the factors affecting the rate of a reaction. Introduction: Chemical reactions take place when reactant particles collide with other reactant particles with a sufficient amount of energy. The energy required for the reaction to take place is known as activation energy. This is written as EAct. In this investigation I am going to investigate the effects that changing one of four factors would have on the speed of the reaction. In this case the experiment I am going to carry out will involve Hydrochloric Acid and Sodium Thiosulphate. I will mix the two substances and time how long it takes for the liquids to produce a liquid which is too cloudy for me to see through. There are four main factors and one smaller one which may limit or increase the rate or speed of the reaction. These are: 1) changing the concentration of the dissolved reactants 2) changing the temperature the reactions take place in 3) using a catalyst 4) changing the surface area 5) and Pressure (with gases) * When you increase the concentration of the reactant you are also increasing the number of particles in the solution. When there are more particles there is a bigger chance of the two reactants colliding and this produces the reaction. * When the temperature is increased, the particles are given more energy from the heat and this makes them move about faster. This means that there are more collisions per second than there would be with a lower temperature. * When a catalyst is used in an experiment, it speeds up the reaction without being changed itself; this means it can be used more than once. It does not work by increasing the number of collisions but works by weakening one or both of the reactants which means that the particles can collide and still react, yet needing less activation energy to produce the reaction. ...read more.


Also I am measuring the concentration of the acid. I changed these two factors as I need to obtain results otherwise the investigation cannot be compared and I can not make any conclusions. Finally the last variables are the ones which I am deliberately changing. The main variable here which I chose to change is the concentration of the Hydrochloric Acid. I could have changed a number of variables which all would have affected the rate of reaction but I decided to choose this one as it is the most easily changed (as described on page four). As mentioned on previous page, I made this test fair by doing several things. I only changed the concentration of the Hydrochloric Acid (and nothing else), I cleaned out the cylinder and conical flask after each use so that no weaker or stronger acid was still present. Finally, I made sure it was always the same person who looked to see if the black tape cross was still visible so that I knew when to stop the stop clock. This was quite important as some people may have better eyesight than others and so may still see the cross when it's not visible to others. I followed my method and obtained a good set of results. I recorded them in a table like this one: Concentration (molar) Time 1 (secs) Time 2 (secs) Time 3 (secs) Average time (secs) Rate of Reaction (3s.f.) Rate of Reaction (standard form ) 0.2 94.86 130.06 114.13 113.02 0.00885 8.85 x 10-3 0.4 88.23 100.50 100.68 96.47 0.104 1.04 x 10-2 0.6 75.72 92.21 82.01 83.31 0.120 1.20 x 10-2 0.8 75.42 75.72 76.28 75.81 0.132 1.32 x 10-2 1.0 60.26 70.84 62.34 64.48 0.155 1.55 x 10-2 The rate of reaction is worked out by doing the sum 1 / x where x = the average time in seconds. The last column on my table has the same results as the 6th column, however they are shown in standard form as they are complicated numbers and it is easier to draw the results on a graph when in this form. ...read more.


However this would be time consuming and at the end of the say all the conical flasks are washed in the same way and so me or a lab technician washing them would not make a difference. After another look at all my graphs, prior knowledge and my tabulated results, I am able to make a final firm conclusion that, when the concentrations of one of the reactants is increased, more particles are in the solution and so there is more chance of the particles hitting other particles. This means there would ultimately be more collisions and so a faster rate of reaction. From this I can also say that a solution with a lower concentration will be the opposite and so will have fewer particles in the solution. Therefore a lower concentration will have a slower rate of reaction There are a few further experiments I could carry out which would relate to this one. Firstly, I could change the substance I am using and I could use something different instead of sodium thiosulphate or even change the acid from hydrochloric to nitric or sulphuric. Another thing I could do to change this investigation is to change a different factor of the five (as mentioned in first two pages of this investigation). I have already used and changed the concentration factor in this investigation and so in another investigation I could change the pressure which when increased, also increases the rate of reaction. The temperature which when higher increases the rate of reaction. The surface area or I could even add a catalyst which would reduce the activation energy, therefore shortening the time to react and increasing the rate of reaction. With each of these I could then carry out the same sort of procedure as in this investigation and could record my results and compare. Overall I feel I have worked well in this investigation, proved a few theories and have achieved my aim of investigating the factors which affect the rate of reaction. ...read more.

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