Determining the Enthalpy Change of the Decomposition of Calcium Carbonate.

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Nathan Stokes                Enthalpy Coursework

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:


           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.   

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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 50cm³ of 2 mol dm³ hydrochloric acid in a 250cm³ beaker.

3. Measure the temperature of the acid using the thermometer provided and record this value. The thermometer should not be left unsupported or it may break.

4. Add the calcium carbonate to the acid. Take the temperature, then again when the reaction is complete. Record this value.

5. Weigh the beaker afterwards.

6. Repeat steps 1 to 5 using an ...

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