by adding to the solution using the same formula for the average temperature, then calculated the uncertainties using the same method as used for the average temperature change.
I then added the mass of the
to the mass of the solution so assuming HCL weighed as much as water and I also added the uncertainties together and then put the mass into kilograms as we will be using an equation requiring kilograms. I so got:
I then needed to calculate the number of moles of both the solution and the
in order to find the limiting reactant as I would need to use the number of moles from the limiting reactant to divide by the heat energy in order to get the molar enthalpy change. I did this as we know we used a 2 mol/l solution of HCl we can calculate the number of moles in .03 l so getting 0.06 moles. For
we know the mass so in order to fin the number of moles we divide the mass by its molar mass so getting .019 moles when we used 2 grams while when we used 3 grams we got 0.28. As the equation fro the reaction states that for every mole of
reacted 2 moles of HCl are reacted it means that a total of .038 of HCl so we can establish that
is the limiting reactant as .03 moles of
would be needed to react the .06 moles of HCl but we only have 0.019 and 0.28.
Now having the mass and the change in temperature and number of moles I can calculate the heat energy using the formula
I then calculated the uncertainty for the heat energy using the equation
so getting the following:
Using hess’s law we can determine that the final enthalpy change for the reaction would be
. Then as I did before I added the uncertainties up getting a final value for the molar enthalpy change of the reaction to be -50± 7
.
Results:
Conclusion:
From our experiment we managed to conclude that the value for the molar enthalpy change is -50±7 Kj
and so we can conclude that this is an exothermic reaction as heat is given off. Using values for bond enthalpies outr teacher Mr. Meisnma resulted having a theoretical value for the enthalpy change of -51 Kj
, which falls inside the range of our uncertainty meaning that our experiment is valid.
From our results we can also conclude that is an error of ±14% in our results, which is very high. This causes our result to be very inaccurate causing our experiment to be very unreliable
From the results we can also conclude that experiment A was exothermic as heat was given off. This can be proven as the temperature change was positive (increasing by an average of 4.8), this means that heat from the particles was given off increasing the kinetic energy of the solution and so increasing the temperature. On the other hand experiment B and C were both endothermic as heat was absorbed. This can be proven due to the fact that the average temperature change was negative -7.4 and -4.1 meaning heat was absorbed from the environment into the particles.
From the results we can also conclude that our experiments were quite fai as for B and C the tests only varied by a maximum of 0.2 as 4.2 -4= 0.2 as well as 7.5-7.3. On the other hand experiment A has a maximum variation of 0.8 as 5.3-4.1=1.2making these results very questionable there is a big difference between the 1st test and the 2nd and 3rd this could probably mean that something went wrong in test one but however this was caused due to having carried out the experiment at difference temperatures.
Evaluation:
Although our results were right proving our experiment valid there are still some things we could improve in order to make our experiment in the future, which are:
On random arrow was that due to shortage in time we carried out the experiment in two days. Those two days happened to have two very different temperatures. As the first day was hotter, as can be seen in the initial temperatures in the results, this caused the rate of reaction to be higher for experiments carried out on the first day so causing a greater heat loss in to the environment due to the increased kinetic energy being higher so causing more friction. Although we took account of the heat loss by drawing the lines on our graphs it still decreases the accuracy of our results as we are not sure that the placing of our lines is perfect causing our results to be less reliable. Also as we discussed in the conclusion the 1st test of experiment A is quite off from the other 2 and this happened to be the on to be carried out on the hotter day, so this problem also caused the uncertainty to increase for experiment A as it is the highest ±5 Kj
causing the quality of our experiment to decrease. In the future we could improve this by carrying out our experiment not only on the same day but carrying out the experiment in an environment with a controlled temperature so making our results more reliable en our experiment as a whole more reliable.
A systematic error during our experiment we used plastic cups meaning that during the carrying out of the various tests they allowed heat to escape so increasing the heat loss during the experiment. As explained in the previous point although we attempted to take account of the heat loss adding lines to our graphs to determine what the actual peak temperature was this is still not full accurate as our graphs not being a straight line the gradient and placement of these lines was decided by eyesight causing there to still be uncertainty and making our results less accurate. In the future we can improve this by using a better insulator so decreasing heat loss and improving our experiment as a whole due to the more accurate results.
Looking at our results we can see we still had noticeable uncertainties this was caused due to the equipment we used. Due to these uncertainties we cause our results to be less accurate but also less reliable as the range of our final results was way too high. In the future we could improve this by using more accurate equipment, an example of this would be using measuring pipettes instead of classic measuring cylinders in order to decrease the amount of systematic errors in our experiment so causing our experiment to be more reliable.
Also another random error in our experiment was cause by the fact that the mass
added was not the same. Although the difference was very small this still caused an uncertainty in our results causing our results to be more inaccurate so making the experiment less reliable. In the future we could improve this by making the masses added as equal as possible in order to make all the tests more equal making our experiment fairer so causing our uncertainties to decrease so causing our results to be more accurate.
by
tomshark95 (student)
