Enthalpy changes - Sample Essay
If we do the same for the ? H2 reaction then we get -91 kJ/mole. If we then use Hess’s cycle to find ? H3 then we get 117. 6 kJ/mole. This shows just how 1i?? C of heat loss can affect the results of the reaction. To combat this next time I will conceal the experiment in a polystyrene cup. Polystyrene has excellent heat absorbing qualities, and would ensure that little heat is lost during the reaction. I could also put a lid on the beaker during the reaction.
Another error was that there was not enough volume of solution for the bulb of the thermometer to be completely submerged. This meant that the thermometer could not record the change in temperature to sufficient accuracy. As I have previously shown the temperature can greatly affect the results so this makes the experiment less reliable. To solve this next time I would simply use more volume of solution so that the bulb is totally covered. Alternatively I could have used a smaller beaker. Out of the two experiments I got the most accurate was the CaO experiment.
This is because of the difficulty of measuring the temperature change. In the CaCO3 reaction, the temp change was only 2. 5i?? C at the most, while in the CaO experiment the greatest change was 10. 5i?? C. This means that a lower resolution of the temperature would affect the CaO reaction less as the change would be of a lower percentage of the recorded change. As well as this we had sufficient weighing scales to measure the amounts of CaO and CaCO3 powder, so any changes would be negligible. Errors in measurement.
An important reason why the results were so different to the prediction was because of the errors in measurement and the fact that some of the measurements made were not very accurate. The first error would be that the measuring cylinder used to measure the acid was too big. We used a 250 ml measuring cylinder when all we needed to use was 50 ml of HCl. This means that we would have an error of up to 3ml while measuring the HCl. If we take this into account in our calculations then the results become very different.