Ar
H1 for the reaction between CaCO3 + HCl
4.2 x 3 x 50 630_ 0.63
1000 1000
2.471 0.025 Ca → 40 x 1 = 40
100 C → 12 x 1 = 12
O → 16 x 3 = 48
= 100
0.63_ 25.2
0.025
H1 = −25.2 Kj mol
H2 for the reaction between CaO + HCl
4.2 x 10 50 1890 2.1
1000 1000
1.426 0.025 Ca → 40 x 1 = 40
56 O → 16 x 1 = 16
→ = 56
2.1 _ 84
0.025
H2 = −84 Kj mol
Due to the fact that I am using Hess’ Law in order to calculate a value for the enthalpy change of the reaction by an indirect method, the H2 must be reversed so the result is changed to a positive number as shown below.
H3
CaCO3 (s) CaO (s) + CO2
H1 HCl H2 HCl
CaCl2 (aq)
H3
CaCO3 (s) CaO (s) + CO2
H1 HCl H2 HCl
CaCl2 (aq)
In order to calculate the H3 you must firstly calculate the enthalpy change of H1 and H2, then reverse the
Evaluation
Errors In Procedure
One error in the procedure of the experiment was hat the calcium oxide and the calcium carbonate were in lumps so the surface area was not as large as it could have been if I would have been provided with fine powered particles, and also the reaction would have been much quicker.
When measuring exothermic reactions, it is important to ensure that when the reaction takes place, as little heat is lost to the environment as possible. This was one error of the reaction. The glass beakers provided for the first attempt were not very efficient at retaining the heat so the results were inaccurate. Due to this, for the second attempt I was provided with a polystyrene beaker, which was a lot better at retaining the heat, although there was some heat loss, as the polystyrene beaker did not have a lid.
Errors In Measurement
One source of error was the use of the thermometers because they had small graduations and a large temperature range of 0 − 250.0 C, this gave inaccurate results as the highest temperature recorded was 27 C, so I should have been provided with a thermometer with a range of up to 50 C.
The measuring cylinder supplied for the measurement of Hydrochloric Acid was 100 cm , whereas I only had measure 50 cm so this may have caused an error. Also when pouring the Hydrochloric Acid into the beaker some may have been left in the bottom of the measuring cylinder meaning the results may have been inaccurate.
Significant Errors
However, a digital thermometer would show much more accurate temperature changes which are particularly vital when dealing with small temperature changes such in the instance of reaction 1. This would decrease the percentage error between actual and theoretical results of enthalpy change.