To determine the enthalpy change of a reaction

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To determine the enthalpy change of a reaction



These are the results I obtained from reacting CaCo3 with Hcl and CaO with Hcl, these 2 experiments were done after one another. The temperature changes of each reaction will then be used to determine the enthalpy change.

Looking at these results it suggests that CaO was a more reactive reaction and a more exothermic reaction than CaCO3 as more energy was released than the reaction with CaCO3. However, we can see that both reactions were exothermic as when the reaction finished both temperatures of the solution after mixing the reactant with the Hcl rise. We can see that these reactions were not endothermic as the temperatures of the solution would have lowered as energy would have been absorbed.

Calcium carbonate, CaCO3 decomposes with heat.

CaCO3 (s) → CaO(s) + CO2 (g)

Calcium oxide reacted with Hydrochloric acid:

CaO(s) + 2Hcl(aq) → CaCl(aq) + H2O

Both calcium oxide and calcium carbonate react readily with 2 mol dm-3 hydrochloric acid (Hcl). The temperature changes during the reactions, these reactions can be measured and the enthalpy change can be determined. ∆H1 and ∆H2 can be calculated. ∆H can be determined simply by measuring the overall energy change for a chemical reaction (quantity of heat absorbed or released) at constant pressure.

Hesses Law

Hess’s law can be stated in 2 ways:

  1. The heat evolved or absorbed in a chemical reaction is the same whether the change is brought about in one step or through a number of intermediate steps.
  2. If a reaction can take place by more than one route, the overall change in enthalpy is the same whichever route is followed.


                      Elements                                                                                                   Compound                                                            



                                  Combustion products         

So using this diagram we can put our experiment into the diagram:


                            CaCO3(s)                                                                                                    CaO (s) + CO2 (g)                                                                    

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