# Determining the Enthalpy Change of the Decomposition of Calcium Carbonate.

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Introduction

Determining the Enthalpy Change of the Decomposition of Calcium Carbonate. The objective of this experiment was to determine the enthalpy change for the decomposition of calcium carbonate with heat, using an indirect method based on Hess' law. The formulae for calcium carbonate, CaCO3, decomposing with heat: CaCO3 (s) heat CaO (s) + CO2 (g) Hess' Law states that ' the total enthalpy change for a chemical reaction is independent of the route by which the reaction takes place provided the initial and the final conditions are the same. The equation for the experiment not just for the decomposition: (H1 (H3 HCl (H2 HCl Both Calcium oxide and Calcium carbonate react readily with 2 mol dm-3 Hydrochloric acid. The temperature changes during the reaction will be measured and the enthalpy changes (H1 and (H2 calculated. From these enthalpy changes the value for (H3 can be calculated. Method 1. Weigh out a beaker containing between 2.4g and 2.6g of calcium carbonate. Record the results. 2. Using the measuring cylinder provided place 50cm� of 2 mol dm� hydrochloric acid in a 250cm� beaker. ...read more.

Middle

27 28 27 Change in temperature during the reaction. ((C) + 8 + 9 + 8 Average Change in Temperature ((C) 8.33 Analysis of the results The data that is in the tables can be combined, in the formula Enthalpy Change = mass of liquid x specific heat capacity of liquid x temperature change or ?H = MC?T, with the specific heat capacity of HCl, which is 4.2 jg -1k -1 and its density, which is 10 g.cm-3. This formula will be used to calculate the values needed to find the (H3. ?H = MC?T CaCO3 = 50g x 4.2 jg -1k -1 x 1.66 (C 2.5g of CaCO3 = 348.6j so therefore: 1g = 348.6 / 2.5 = 139.44j Mol mass of CaCO3 = 100 139.44 j x 100 = 13944 mol -1 (H1 = -13.9 Kj mol -1 ?H = MC?T CaO = 50g x 4.2 jg -1k -1 x 8.33 (C 1.4g = 1749.3 1g = 1749.3 / 1.4 = 1249.5j Mol mass of CaO = 56 1249.5 x 56 = 69972 mol -1 (H2 = - 69.9 Kj mol -1 Using Hess' Law. ...read more.

Conclusion

Another error that affected the results was that the thermometer is only accurate to 1 (C this affects the accuracy of the results. An improvement that could be made to this is to use a more accurate thermometer i.e. an electric thermometer. A smaller beaker should also have been used instead of a large beaker, so the acid was at a higher level so that the bulb of the thermometer was totally covered by the solution. An error, which also caused problems with accuracy, was that two different weighing scales were used due to availability. One scale measured to two decimal places where as the other only measured to one, the results would have been more accurate if the two decimal scales were used. An improvement that could have been made to my experiment is that the CaCO3 should have been used as a powdered form instead of a lump form as it would have a higher surface area, so the reaction would take place quicker. If the reaction is faster then it is less likely that so much heat will be lost. Nathan Stokes 1 Enthalpy Coursework ...read more.

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