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Heat of Reaction - Dissolving Magnesium in acid

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Heat of Reaction - Dissolving Magnesium in acid Planning The aim of this investigation is to study the temperature increase when magnesium is dissolved in Hydrochloric acid. This reaction is an exothermic reaction so some heat will be given off, but the aim of the investigation is to find if the amount of heat given off will vary when the length of magnesium is changed. The reaction that will take place is as follows: Magnesium + Hydrochloric Magnesium + Hydrogen Acid solution Chloride solution Prediction I predict that as the length of magnesium is increased, the temperature change of the Magnesium Chloride solution will increase. I also think that the relationship between the two is directly proportional. Because of this I predict that if the length of magnesium is doubled, the temperature will also double. Explanation of prediction I predict that as the length of magnesium is increased, the temperature change of the Magnesium Chloride solution will increase. This is because as the amount of magnesium is increased, more metallic bonds are broken. Therefore more bonds will be formed to make the products. It is the bond forming that gives off thermal energy, so if more bonds are being formed, more heat will be emitted. This means that the length of magnesium is directly proportional to the heat produced. Put simply, the chemical reaction is bond breaking followed by bond forming. In an exothermic reaction bond forming releases more energy than is required bond breaking, so surplus energy is given out. Therefore, more magnesium means more bond changes and ultimately greater temperature changes. I also predict that if the length of magnesium is doubled, the temperature increase will also double. ...read more.


This is so any anomalous results can be recognized and repeated until a result that fits the line of best fit on the graph is achieved. As well as displaying results on a graph, they should also be recorded in the following table: Length of Mg (cm) Start Temp (�C) Finish Temp (�C) Temp Change (�C) 0 0.0 0.0 0.0 2 20.0 23.0 3.0 4 20.0 26.0 6.0 6 20.0 29.0 9.0 8 20.0 32.0 12.0 10 20.0 35.0 15.0 12 20.0 38.0 18.0 A column for the molarity and volume of the acid is not included because it will be kept at a constant. Analysis It has been found that as the length of magnesium increases, so does the temperature change. The evidence of the results from the experiment strongly confirms the predictions. This is so because the prediction was 'as the length of magnesium is increased, the temperature change of the Magnesium Chloride solution will increase', this was confirmed by the results. The results recorded show clearly the temperature increase, e.g. in my results the temperature change was 3, 6, 9, 12, 15 and 18�C. It was also predicted how the graph would look, this graph was identical to the graph produced from the results. The results support the prediction well but the changes are not as exact as we would have liked because we did the experiment with apparatus that was not entirely error free. The class results are as follows: Length of Magnesium (cm) T E M P (?C) C H A N G E 0 0 0 0 0 0 0 0 0 0 0 0 2 4.0 4.0 2.5 4.5 4.0 3.0 4.5 3.0 1.0 3.0 4.0 4 6.5 7.0 6.0 7.5 7.0 6.0 7.0 6.0 6.0 6.5 9.5 6 10.0 10.0 ...read more.


This would have scraped off the layer of oxide and given more accurate results. 2. Although the polystyrene cup was effective in reducing heat loss, it could have been made even better if there had been two polystyrene cups instead of just the one. Also on the subject of insulation, the hole in the wooden lid for the thermometer was considerably larger than it needed to be, so heat will have escaped that way also. To prevent this heat loss, a smaller hole should be used. 3. The same polystyrene cup was used for each test. This meant that there would still have been some acid from the previous test in the cup when being used. This could have affected the results. To stop this, a new, sterilized cup should be used each time. All of these points are fairly insignificant own their own, but together they could make considerable changes to the results recorded. Numerous other investigations could be done in relation to this one. These include: 1. Investigating how other metals react with the hydrochloric acid. This would show where metals fit into the reactivity series, i.e. a metal higher up the reactivity series than magnesium would cause a bigger temperature increase and visa versa. 2. Investigating how other acids such as Sulphuric acid, nitric acid and carbonic acid react with magnesium. Do they produce a greater amount or a smaller amount of thermal energy than hydrochloric acid? 3. Investigating how magnesium would react if the weight were regulated instead of the length. Would a change in surface area affect the amount of heat produced? (However, this would be incredibly difficult to do as 2cm of magnesium has a very small mass.) 4. Investigating the volume of hydrogen being given off as well as the amount of heat being given off. Are the two directly proportional? [LL1] Danny Longman November 2001 4 ...read more.

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