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To investigate the factors that affect the amount energy produced in neutralisation reactions.

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Introduction

CHEMISTRY INVESTIGATION 2003 Aim: To investigate the factors that affect the amount energy produced in neutralisation reactions. The Aim of this investigation is to see how the dependant variable, the heat realised as a result of neutralisation reaction changes as one independent variable is changed, and to find why these changes occur. Only one variable will be changed. This is because if more than one is changed as well, we will not know which factor is responsible for the change. The variables are specified below, along with the one that I have decided to vary. Variables The following variables can be controlled during the experiment and will be the ones we can change in the investigation. The one that I have chosen is listed below. These variables are called independent variables, and will allow us to assess and investigate the effect on the heat released by neutralisation reactions. 1. The concentration of the acid or the alkali in the reaction could be decided to be varied (I have used the term alkali rather than base, because the substance will already be dissolved in water which is the definition of an alkali). To carry this out, one would have to obtain acids or bases or both of varied concentration, by obtaining a fairly strong concentration, and then diluting it down to get varied concentrations. This procedure would be time consuming, and there would certainly be room for much error, as the concentration may not be measured out correctly, leading to inaccuracy. A general trend that would probably be seen is that, as the concentration goes up, so does the heat released by neutralisation. This is because there are more ions in a solution of a higher concentration. I have listed this variable as one, but it is really two different variables: one can either vary the concentration of the acid or that of the base. ...read more.

Middle

If the reaction is endothermic, there are obviously more bonds to be broken than have been made. It is also the case that stronger bonds take more energy to break than weaker bonds, and when stronger bonds are made, they release a greater amount of energy than when weaker bonds are created. Going by this, it is clear that every single reaction will have, to some degree, an energy change. Another factor discovered is that the amount of energy taken in by breaking bonds equals the amount of energy released through the creating of new bonds. The amount of energy taken in or released can be expressed in kilojoules or joules, the SI unit for energy. To make the investigation fair I will express my values per mole. The energy changes that occur in reactions can be shown using energy level diagrams. In these diagrams, energy goes on the y-axis, and the x-axis is labelled as the reaction process, which shows the progress of the reaction. These diagrams do not show any numerical values, they are only used to show trends of energy changes in exothermic and endothermic reaction. The enthalpy diagrams are shown below, for both endothermic and exothermic reactions The equation used to work out the energy transferred is ENERGY (KJ)= S.H.C X MASS (in g) X temperature change (in Kelvin) Exothermic Reaction Endothermic Reaction Products Reactants Products Reactants Progress Of reaction Progress Of reaction I have chosen to vary the type of the acid, for my investigation. I have decided that I am going to have a wide selection of different acids to investigate, but for the alkali, I am only going to have one weak and one strong one. I have chosen to vary the factor of type of acid, rather than volume or concentration (of either acid or alkali), because it would allow a simple and easy procedure. Another reason for choosing this variable is that it will allow a multitude of different combinations that will lead to clear-cut conclusions. ...read more.

Conclusion

It is known that the breaking of bonds causes energy to be taken in, and when bonds are made, energy is given out. Another reason for a stronger acid producing a higher value for the heat of neutralisation is because it has more free H+ ions. I have deduced this because it is known that in a strong acid, all of the molecules are dissociated into their component ions. When the strong acid is used to neutralise the alkali, a more vigorous reaction would occur as a result of there being more H+ ions in the solution to neutralise the OH- ions in the alkali to give out more heat. To aid my evaluation of my results I have calculated the enthalpy changes for each of the acids used. I will compare these results with the change in kelvin results. Acid Average temperature change/Kelvin Specific Heat Capacity Mass/grams (including alkali) Energy change in Joules Sulphuric 11.0 4.2 50.0 2310.0 Nitric 7.0 4.2 50.0 1470.0 Hydrochloric 8.5 4.2 50.0 1785.0 Ethanoic 6.7 4.2 50.0 1407.0 Methanoic 6.5 4.2 50.0 1365.0 Citric 9.0 4.2 100.0 3780.0 Change in Joules Graph Change in Kelvin results graph Further Analysis The graphs for both change in Kelvin and Joules, have very similar patterns. The only difference between both is that Citric acid gives 3780.0 joules, which is 1470.0, more joules than sulphuric acid, which has a higher change in Kelvin than compared to citric acid. The reason for there to be a higher amount of energy maybe due to the fact that a higher volume is used for the citric acid than sulphuric acid, which may link to the fact that a higher volume of acid gives a higher enthalpy change. I believe my prediction was partially linked to the results recorded, mainly due to the fact that the weaker acids gave higher readings than expected, like Ethanoic and that the stronger acids gave lower than expected readings, like Hydrochloric acid. Overall I believe my results showed the trend that would be expected. ...read more.

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