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The effect of temperature on the rate of reaction

Extracts from this document...

Introduction

Simon Flood Mr Macintosh 11C Chemistry Course work 11Hawking School Number: 37625 Candidate number: Investigation: The effect of temperature on the rate of reaction We are conducting an experiment to ascertain whether Magnesium strips will dissolve quicker in a solution of Sulphuric Acid at various temperatures. During the experiment I am trying to find out whether temperature will have an effect on the rate of a reaction, and also what the effect on the reaction is. Throughout the experiment I shall test the following reaction: Magnesium + Sulphuric Acid ? Magnesium Sulphate + Hydrogen Mg (s) H2 (aq) MgSO4 (aq) H2 (g) Preliminary Test: Before starting our experiment we had to think ahead to any problems we may encounter during the experiment in and what would be the best way to resolve them. There were three main areas we decided it would be necessary to test, and these are listed below along with how we have decided to resolve them: * Exothermic Reaction: The majority of reactions give off excess heat, which basically means they are exothermic, and this would affect the results of our experiment as we are testing how temperature change can effect the rate of reaction. Basically this shows us that we need to find the activation energy. Activation energy is the minimum amount of energy put into the reaction to get the minimum out of it. Reactants have an amount of energy. You need to put the same amount of energy in to get the Activation energy. Following is a table showing how different concentrations of sulphuric acid and lengths magnesium strip affect the temperature: Mg strip(cm) Temp before(oc) Temp after (oc) Time of reaction (s) Vol. Acid(cm3) 0.5 20.0 22.0 39.91 30.0 1.0 20.0 21.0 41 40.0 1.5 20.0 22.0 69.91 20.0 Previously we knew that the rate of a reaction will change during the reaction. It is greatest at the start, but declines as the reaction proceeds because reactants are being used up. ...read more.

Middle

In our case dilute acid is the concentration and there are fewer acid particles, therefore there are less collisions between acid particles and magnesium atoms and therefore the reaction takes longer. - Size of Solid Particles (Surface area) increases collisions: If one reactant is a solid then obviously breaking it up will split these solid particles up again increasing collisions due to them being bigger. The greater the surface area, then the faster the rate of reaction will be, in the smaller particles the entire surface exposed for reaction is greater therefore more collisions occur and due to the increase in collisions, the rate of reaction is obviously going to be faster. - Catalyst increases the number of collisions: A catalyst works by giving the particles an extra surface to bounce off of and again increasing collisions. Catalysts offer an alternative path with a lower activation energy. Before reactants are able to convert into products, they must overcome an energy barrier. This is the slowest part of the reaction. The energy needed for a reactant to overcome the energy barrier is called the activation energy. Effectively, a catalyst lowers the activation energy, therefore speeding up the reaction (ie, the reaction rate increases). Nb: a catalyst is a substance that changes the rate of a reaction, but remains chemically unchanged itself. The Boltzmann theory relatively fits in with my predictions/scientific evidence, therefore I shall include it below: We can now look at the Boltzmann theory graph: - I have found looking at the GCSE double award Chemistry revision guide the Maxwell Boltzmann distribution. Looking at the Boltzmann Distribution we can see that an increase in temperature increases the rate of reaction. Below is the diagram: We can see this by the fact that: -Molecules in larger numbers exceed the activation energy. -The faster the molecules travel the more frequent the collisions are. -The Boltzmann distribution curve is displaced with a lower peak to the right increasing the average energy. ...read more.

Conclusion

Further Work To improve my results further, I could repeat the experiment three or four times and find the average, rather than only repeating the experiment once and finding averages of the minor experiments within this larger one. Factors that I know, but did not take into account in this experiment, are that - (1)The reaction between magnesium and hydrochloric acid is an exothermic one (which I found out by placing a thermometer in the mixture during the reaction and observing that the level in the thermometer had increased) - (2)The reaction gives off a high percentage of hydrogen gas (this is due to the fact that when the magnesium reacts with hydrochloric acid, it displaces the hydrogen from the acid, as it is placed higher than Hydrogen in the reactivity series). The problem with (1) is that, due to the reaction being exothermic, the reacting particles will gain more energy from the increasing temperature and thereby reach the required activation energy in a shorter time. This could increase the rate of reaction and lead to inaccurate results. I could investigate a method for keeping the reactants at a constant temperature. Taking (2) into consideration, I could repeat this experiment, this time recording the amount of hydrogen gas given off from each concentration of acid. I could use a gas syringe to collect the gas that would be given off from the experiment between the two substances. I believe this is a better way to investigate the rate of reaction(on temperature) as it would be possible using these results only, to calculate the initial rate of reaction. Thus could prove to be a more accurate set of results rather than averaging the rate of the reaction after the actual experiment, as I would then know the real/actual rate of reaction for magnesium and hydrochloric acid combined. Investigating the reaction of Magnesium with different types of acid each time could further enhance the investigation. Hydrochloric, Sulphuric and Nitric acid would all react differently and perhaps give a greater understanding into the reaction mechanism with a clear pattern linking them all together. ...read more.

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