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An Experiment to Determine the Enthalpy Change for the Decomposition of Calcium Carbonate.

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Introduction

An Experiment to Determine the Enthalpy Change for the Decomposition of Calcium Carbonate Aim: to determine the enthalpy change for the decomposition of calcium carbonate CaCO3(s) CaO(s) + CO2(g) Problem: this experiment cannot be done because many reactions have enthalpy changes that cannot be found directly from a single experiment due to many factors which includes the fact that you cannot measure the amount heat that has been put in from the Bunsen burner. So in order to determine the enthalpy change for the decomposition of calcium carbonate Hess's Law needs to be used because it provides a method for the indirect determination of the enthalpy changes. Hess's Law is an extension of the First Law of Thermodynamics. Hess's Law states that, if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route. So I will measure the temperature changes when calcium oxide and calcium carbonate reacts with hydrochloric acid solution. Then I can use a Hess' Law cycle to calculate the enthalpy changes using the formula: Heat produced = mass of solution x change in temperature x specific heat capacity of water This equation will help me to calculate the enthalpy changes of each experiment. I then drew a Hess' Law cycle to illustrate the enthalpy values. CaCO3(s) CaO(s) + CO2(g) ?H? CaCO3(s) CaO(s) + CO2(g) R2 + 2HCl acid + 2HCl acid R1 CaCl2(aq) ...read more.

Middle

Safety Safety is very important and it is necessary to follow safety procedures. It is important to wear eye protection when working with any acid. Also long hair should be tied back. Be careful when handling glass ware and keep stools under bench so that they are not in the way. The chemicals used are corrosive it is important to take extra care while working around them. Especially when handling with the hydrochloric acid (HCl) this is corrosive and it may cause burns when it in contact with skin. The vapour is very irritating to the respiratory system. The hazards of the chemical were taken from the hazard cards. Accuracy In order to reduce errors it is necessary to choose accurate and reliable equipment. That why using measuring cylinder would be a good choice. This instrument has an accuracy of �0.05cm�, which is suitable for the experiment and should produce accurate and reliable results. Calculations Once I done the experiment I will use the results to calculate the enthalpy change for the decomposition of calcium carbonate (CaCO3). But first I will need to calculate the heat produced from calcium carbonate (CaCO3) reacting with hydrochloric acid (HCl) and calcium oxide (CaO) reacting with hydrochloric acid (HCl). To do this I need to use the formula: Heat produced = mass of solution x change in temperature x specific heat capacity of water Once I work out the heat produced for calcium carbonate (CaCO3) ...read more.

Conclusion

* The main different in value would be due to heat loss cause so much heat is loss when replace the lid to the polystyrene beaker after the calcium oxide and calcium carbonate put in. Also through the actual polystyrene beaker itself, the thermometer and the hole where the thermometer is put through. * Not all the heat goes into the solution some would go into the thermometer, the polystyrene beaker so the heat is being absorbed by other objects instead of the solution. * The concentration of the calcium oxide or calcium carbonate may not have been exactly right. * Not all of the calcium oxide reacted in the second experiment cause there was still calcium oxide in the beaker at the end. That meant that the enthalpy value I got for calcium oxide is wrong. * Because there were so much errors in both experiments that meant the final change in heat for the decomposition of calcium carbonate was very inaccurate (74.6%) due to all the factor mentioned above. Improvements > If equipment rinsed wait till it's dry before using it. > Use a container which will not absorbed as much heat as the polystyrene beaker does > Maybe conduct the experiment in a close container where not so much heat can escape into the air. > Or extend the experiment by doing exactly the same method but timing it so by recording down the temperature for every 30 seconds. This could be done by computer which would reduce the error of reading the thermometer wrongly. ...read more.

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