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Determination of the Heat of Formation of Calcium Carbonate

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Introduction

Experiment 6 Determination of the Heat of Formation of Calcium Carbonate Name: Leung Dik Ka (14) Name of partner: Lee Wai Chi (13) Date: 5/11/2008 Title of the experiment: Determination of the Heat of Formation of Calcium Carbonate Aims: To determinate the heat of formation of calcium carbonate by finding the temperature change in two reaction. Introduction Heat of formation is the enthalpy change when one mole of product is formed from its constituent elements under standard conditions. The equation for the formation of calcium carbonate from its elements under standard conditions is Ca(s)+C (graphite)+O2 (g) �CaCO3(s). The standard conditions are defined as elements or compounds in their normal physical states, under a pressure of 1 atm (101 325 Nm-2) and a temperature of 250C (298 K). Procedure A) Reaction of Calcium with dilute hydrochloric acid 1.1g of calcium metal was weighed out approximately. The weighing was recorded. 2.100cm3 of 1M hydrochloric acid was measured out by a measuring cylinder and was placed in a vacuum flask . 3. The temperature of the acid was determined and recorded. ...read more.

Middle

Instead, the calcium metal is a limiting agent. B) Reaction of calcium carbonate with hydrochloric acid: The ionic equation for the reaction is CO32- (aq) +2H+(aq) ?CO2 (g) + H2O (l) Assuming that the solution in the plastic beaker has the same specific heat as water, the heat of formation of CO2 (g), H2O (l) and CaCl2 (aq) was evolved in the reaction between the hydrochloric acid and the amount if calcium carbonate used. Assume that the density of the solution is the same as that of water, i.e. 1 g cm-3 Mass of the hydrochloric acid = 100 cm3 ? 1 g cm-3 = 100 g = 0.1 kg Heat given out = 0.1? 4200 ?1 = 420J Number of moles of CaCO3 = 2.39 ? (40.1 +12 +16?3) = 0.0239 mol Heat evolved by one mole of calcium atoms = 0.42 ? 0.0239 = 17.6 kJ mol -1 Discussion In these two experiments, there are some errors. There was heat loss by the system to the thermometer and the vacuum flask, otherwise, the temperature will drop even lower. ...read more.

Conclusion

,in order to enable us to calculate the heat of formation of calcium carbonate. ?HfO (CO2 (g)) = -393.5 kJ mol -1 ?HfO (H2O (l)) = -285.5 kJ mol -1 Heat of formation of calcium carbonate = ?H1 + ?Hf (CO2 (g)) +?Hf (H2O (l))- ?H2 = -421+(-393.5)+(-285.5)- (-17.6) = -1082.4 kJ mol -1 In order to achieve the answer, Hess's law is used. Hess's law states that the total enthalpy change of a reaction is independent of the route by which the reaction takes place. In other words, the standard enthalpy change of a reaction depends on the differences in standard enthalpy between the reactants and the products. It means that the enthalpy of the reaction system is conserved. As the absolute enthalpy of a substance isn't possible to be determined and only the difference between reactants and products can be measured experimentally. This law helps us to define the standard enthalpy change of a reaction. Conclusion After carrying out the experiment, we found out that the heat of formation of calcium carbonate was -1082.4 kJ mol -1, by applying the Hess's law, using the data in reaction of dilute hydrochloric acid with calcium and calcium carbonate, and the theoretical values of ?HfO (CO2 (g)) and ?HfO (H2O (l)). ...read more.

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