2
Temperature at start. 20ºC 24ºC
Temperature at end. 75ºC 79ºC
Temperature rise. 55ºC 55ºC
Average rise, 55 + 55 = 55
2
Ethanol
Actual heat combustion 1370 kj/mol
Test one. Test two.
Mass of burner at start. 274.82 246.83
Mass of burner at end. 246.83 245.53
Mass of alcohol used. 0.99 1.3
Average mass = 0.99 + 1.3 = 1.145
2
Temperature at start. 22ºC 22ºC
Temperature at end. 91ºC 88ºC
Temperature rise. 69ºC 66ºC
Average rise, 69 + 66 = 67.5
2
Molecular masses, Butanol, 74 Ethanol, 46
Butanol heat given out = 20 * 4.2 * 55
= 4620 actual result, 2673
Ethanol heat given out = 20 * 4.2 * 66
= 5544 actual result, 1370
The following method will be the one followed throughout the experiment: -
* Firstly collect all the necessary equipment and safety goggles. Set up the equipment being used. Collect each alcohol to be tested and place the first one on the heatproof mat.
* Measure a distance of 5cm from the top of the alcohol burner to the base of the calorimeter and clamp in place.
* Measure 200cm³ of water and place in the calorimeter. Weigh the alcohol burner and record the weight in a results table.
* Note the starting temperature of the water from the thermometer and then light the alcohol burner.
* Keep checking the rise of temperature on the thermometer throughout the experiment.
* Additionally throughout the experiment, hold on to the thermometer and stir the water around making sure that it does not touch or rest on the calorimeter, as this could unfairly alter the thermometer reading.
* Once a reading of 30ºC has been recorded, put out the flame on the alcohol burner by placing the lid back on top, starving the flame of oxygen.
* Re-measure the weight of the alcohol burner and note down the weight and the change of weight between before and after the experiment.
* Repeat the whole experiment three times for each of the 5 alcohols. Recording the weights of the alcohol burners each time.
* Once the experiments have been completed of a total of 15 times. Collect all data, and results in a table and calculate the fuel used and the heat energy that was given out.
The accuracy of the weighing scales is to one decimal place (1.d.p), which gives a +- 0.05g inaccuracy and the accuracy of the thermometer is to 0.d.p. So there is a +- 0.5ºC possibility of anomalous results. The experiments will be repeated three times each to lessen the chance of an anomalous result. The mean amount will then be calculated and used to plot a graph.
Further to my prediction, the carbon chains increase be a single carbon bond each time, meaning there will be a specific rise in the energy give out of 496 kJ/mol.
The bond structures for each of the alcohols.
Methanol
H
HCOH single carbon bond.
H
Ethanol
H H
HCCOH two carbon bonds
H H
Propanol
H H H
HCCCOH three carbon bonds
H H H
Butanol
H H H H
HCCCCOH four carbon bonds
H H H H
Pentanol
H H H H H
HCCCCCOH five carbon bonds
H H H H H
The following calculations are for the ideal results. These will also be plotted onto the graph so a comparison will be able to be made between the actual results and the ideal ones.
Methanol
CHзOH + 1½ O2 ~ CO2 + 2H2O.
3*CH 3*412 + 1½ * O=O 1½ * 496 ~ 2 * C=O 2 * 743 + 4 * OH 4 * 436
1*CO 360
1*OH 463
1236 ~ 1486
360 +1852
463 3338
+744
2803
Energy difference = 2803 3338
= -535
Ethanol
C2H5OH + 3O2 ~ 2CO2 + 3H2O
1 * CC 348 3 * O=O 3 * 496 ~ 4 * C=O 4 * 743 + 6 * OH 6 * 463
5 * CH 5 * 412
1 * CO 360
1 * OH 463
348 2972
2060 +2778
360 5750
463
+1488
4719
Energy difference = 4719 5750
= -1031
Propanol
C3H7OH + 4½O2 ~ 3CO2 + 4H2O
2 * CC 2 * 348 4½ * O=O 4½ * 496 ~ 6 * C=O 6 * 743 + 8 * OH 8 * 463
7 * CH 7 * 412
1 * CO 360
1 * OH 463
696 4458
2884 + 3704
360 8162
463
+ 2232
6635
Energy difference = 6653 8162
= -1527
Butanol
C4H9OH + 6O2 ~ 4CO2 + 5H2O
3 * CC 3 * 348 6 * O=O 6 * 496 ~ 8 * C=O 8 * 743 +10 * OH 10 * 463
9 * CH 9 * 412
1 * CO 360
1 * OH 463
1044 5944
3708 +4630
360 10574
463
+ 2976
8551
Energy difference = 8551 10574
= -2023
Pentanol
C5H11OH + 7½ O2 ~ 5CO2 + 6H2O
4 * CC 4 * 348 7½ * O=O 7½ * 496 ~ 10 * C=O 10 * 743 +12 * OH 12 * 463
11 * CH 11 * 412
1 * CO 360
1 * OH 463
1392 7430
4532 +5556
360 12986
463
+ 3720
10467
Energy difference = 10467 12 986
= -2519
Table of Results
Analysis
By looking at my graph I can see that as the number of carbons in the carbon chains increase, the energy produced increases also. The increase in the energy produced as the chain length increases, is due to more energy being needed to break more bonds and also for some new bonds to be made. By looking at the experimental results on the graph, it can be seen that the increase in enthalpy change is proportional to the length of the carbon chain. This is because as the carbon chain increases each time, an extra CC bond and two CH bonds are present and so a certain amount of extra energy is needed each time to break these extra bonds. There are more bonds to be broken and more bonds to be made overall which then leads to a higher enthalpy change. Also by looking at the experimental results, it can be seen that they support my hypothesis. Although the actual results were less than the ideal results, they still followed the trend of an increase in the number of carbons means also an increase in the produced energy. The energy is released in bond making when the atoms collide together to make the new bonds.
With the ideal results, the energy produced is directly proportional to the length of the carbon chain. Whereas with the experimental results, energy is lost which means the energy produced is only proportional to the number of carbons. The energy loss is due to bad insulation or by excess energy escaping through the top of the calorimeter as a lid was not used. Additionally there is the possibly of anomalous results from either the balance or the thermometer readings.
Evaluation
The results collected were fairly accurate and reliable to the method used. The results were plotted on the graph and then a line of best fit was drawn. The results were all very close to the line of best fit except for one anomalous result. This anomalous result could have been due to an inaccuracy of measurement from possibly the thermometer or the balance. The thermometer had an accuracy to 0 decimal place (0.d.p) with the possibility of a +-0.5ºC change. The balance had accuracy to 1.d.p. with the possibility of a +-0.05g change.
The reliability of the method was quite reliable as the experiment was repeated three times on each of the alcohols gaining a range of results. Some possible improvements to the method might be for the experiments to be repeated several more times so an even greater range of results could be collected. Additionally a balance with accuracy of to more decimal places could be used to gain a more accurate weight of the alcohol burners. Additionally, a data logger could be used instead of a thermometer so the temperature readings could be more accurate and reliable. Additionally, the use of lid could be used to reduce the loss of heat energy from the top of the calorimeter, or the use of an insulated cup. By using an insulated cup, the amount of waste energy lost would be reduced making the results more accurate and reliable overall.
