The Enthalpy Change of the Thermal Decomposition of Calcium Carbonate
Results:
For CaCO3: T1 = 17
T2 = 19
DT= 02
using 2.57g of CaCO3
For CaO: T1 = 18
T2 = 27
DT= 09
using 1.39g of CaO …show more content…
Then, having converted the energy intake into kJ (-1.9278 kJ), we put the data into this formula:
DH= (E ¸ 1000) ¸ No moles
Getting:
DH = (-1927.8 ¸ 1000) ¸0.025
= -1.9278 ¸0.025
= -77.112
» -77 kJ mol-1
Now we have found both measured enthalpy changes, we can work out the enthalpy change for the thermal decomposition of calcium carbonate. This is done by following Hess's Law, which states that "The enthalpy change in a reaction is the same, independent of the number of steps taken, provided the reactants and products end up in the same states that they would ordinarily be". It is this principle that is behind this experiment - since we are dissolving both chemicals in HCl, and starting with solid calcium carbonate, calcium oxide and carbon dioxide, we can work out the enthalpy change using this law. This is best done by constructing a triangle, as shown below:
[IMAGE] CaCO3 DH3 CaO + CO2
[IMAGE]
[IMAGE]
DH1 DH2
CaCl2
We draw out the triangle, and can see that, in order to get from calcium carbonate to calcium oxide, we must go in the same …show more content…
Evaluation:
There were a large number of problems with this experiment, the most significant source of error being the heat loss to the apparatus. The reactions took place in a glass beaker. Glass has a relatively high heat capacity, and so a large amount of heat which is either taken in or given out is lost to the apparatus. This is obviously a major problem, especially with the reaction of calcium carbonate with HCl, as this does not appear to have a very large change in temperature, so every slight bit of absorption by the apparatus will have a large effect on the temperature change, and consequently the enthalpy change. Th other piece of apparatus that will have absorbed a lot of heat is the thermometer itself, as it is also made of glass, and so also has a high heat capacity, leading to similar problems as with the beaker. Another inaccuracy in the experiment was the time at which
Results:
For CaCO3: T1 = 17
T2 = 19
DT= 02
using 2.57g of CaCO3
For CaO: T1 = 18
T2 = 27
DT= 09
using 1.39g of CaO …show more content…
Then, having converted the energy intake into kJ (-1.9278 kJ), we put the data into this formula:
DH= (E ¸ 1000) ¸ No moles
Getting:
DH = (-1927.8 ¸ 1000) ¸0.025
= -1.9278 ¸0.025
= -77.112
» -77 kJ mol-1
Now we have found both measured enthalpy changes, we can work out the enthalpy change for the thermal decomposition of calcium carbonate. This is done by following Hess's Law, which states that "The enthalpy change in a reaction is the same, independent of the number of steps taken, provided the reactants and products end up in the same states that they would ordinarily be". It is this principle that is behind this experiment - since we are dissolving both chemicals in HCl, and starting with solid calcium carbonate, calcium oxide and carbon dioxide, we can work out the enthalpy change using this law. This is best done by constructing a triangle, as shown below:
[IMAGE] CaCO3 DH3 CaO + CO2
[IMAGE]
[IMAGE]
DH1 DH2
CaCl2
We draw out the triangle, and can see that, in order to get from calcium carbonate to calcium oxide, we must go in the same …show more content…
Evaluation:
There were a large number of problems with this experiment, the most significant source of error being the heat loss to the apparatus. The reactions took place in a glass beaker. Glass has a relatively high heat capacity, and so a large amount of heat which is either taken in or given out is lost to the apparatus. This is obviously a major problem, especially with the reaction of calcium carbonate with HCl, as this does not appear to have a very large change in temperature, so every slight bit of absorption by the apparatus will have a large effect on the temperature change, and consequently the enthalpy change. Th other piece of apparatus that will have absorbed a lot of heat is the thermometer itself, as it is also made of glass, and so also has a high heat capacity, leading to similar problems as with the beaker. Another inaccuracy in the experiment was the time at which