To perform an experiment in the labs to determine the heats of combustion of selected alcohols and then to use this Information and the gathered data from chemical data sources to determine trends In the longer chain alcohols. The Variables that MUST be controlled throughout the experiment are: ; The height from spirit burner nozzle to the base of the water filled beaker ; Alarm drafts around the room must be kept to minimum so as to keep the heat on the base of the beaker a Keeping room temperature constant will enable the constant Temperature. exults to be a little more accurate and reliable The Variables that MUST be measured and recorded before the experiment are: ; The weight of the beaker before and after the water has been added to it. ; Initial temperature of the water. The weight of the spirit burner before and after the alcohol has been added. Equipment The equipment needed to perform this experiment Is: Spirit Burner (Lengthen the wick as to allow for a greater flame produced). Beaker Tripod (Preferably wide bottoms as to allow the Ralston of the spirit burner). ; Retort stand Boss head clamps Thermometer Water Alcohol Accepted figures from chemical data sources Estimate heat of combustion on breaking and formation of chemical bonds ; Pen/ pencil for recoding results ; Results table. Safety glasses Matches Scales Measuring cylinder Method In the experiment that follows the dependent variable is the heat energy in the water while the burning of the different types of alcohol is the independent variable.
Variables that must be measured but not necessarily controlled during the experiment are: ; Weight of the alcohol and spirit burner before and after they have stopped burning in grams (g). ; Final Temperature of the water in degrees Celsius(C ) ; Mass of the water and beaker in grams (g) Make sure to read through the whole experiment and be familiar with It before attempting It. 1) Set up equipment as shown In diagram below: 2) Record the following : Weight of beaker without and with water calculating amount of water in beaker (g). Weight of spirit burner with alcohol in it (g). 3) Remove all flammable material away from experiment and put on glasses and other necessary safety equipment. 4) Begin burning the alcohol from spirit burner while making sure to minimize air drafts and distance between the spirit burner nozzle and the base of the beaker. ) When you have deemed the water has risen enough in temperature or enough alcohol has been burnt off turn off the spirit burner and quickly record the final temperature of the water. (Burn for at least 5 minis to burn off a measurable amount of alcohol). ) Measure and record the following variables: Weight of spirit burner after burning (CAREFUL it may still be hot). ; Mass Of water (Should still be the same but might have lost some due to evaporation). 7) Convert the weight of the alcohol in grams to amount of moles. 8)Calculate Joules per gram with -MICA equation then calculate Joules per mole by using the moles ormolu. 9) Compare calculations against their accepted figure from chemical data sources and the estimate based on the breaking and forming of chemical bonds.
Weight of Beaker without water(g) Weight of Beaker with water(g) Mass of water(g) Initial Temperature of water(CO) Final Temperature of water(CO) Change in Temperature of water(CO) Weight of spirit burner and alcohol before burning(g) Weight of spirit burning and alcohol after burning(g) Amount of alcohol burnt(g) Accepted Joules per gram and per mole from Chemical data sources Methanol: -726 k mol-l Methanol: -jack/g Ethanol :-1367 k mol-l
Ethanol: -jack/g I-proposal :-2021 k mol-l Proposal: -jack/g I-tonal :-2676 k mol-l Butane: -36 k/g Calculated Joules per a gram and per a mole from bond energies Methanol: -666 k mol-l Methanol: -20. 7 k/g Ethanol: -1317 k mol-l Proposal: -1876 k mol-l Butane: -2489 k mol-l Ethanol: -28. 5 k/g Proposal: -30. 7 k/g Butane: -33. 5 k/g In my experiment I burnt the alcohol proposal. The theoretical energy per a mole of this was -2021 k per Mole but in the experiment I ended up getting an energy yield of -kick] per a Mole . The reasons this has happened is because of the following: ;
Incomplete Combustion: in the theoretical result it presumes your experiment achieves complete combustion. This was definitely not achieved as carbon was a product of the reaction thus meaning there was an incomplete combustion resulting in a much lower energy yield. ; Heat Dispersion: In the theoretical results it assumes that 100% of energy released is captured into the water to be measured. This is not practical in a combustion of alcohol as the heat radiates in all directions and not directly into the water causing not 100% of energy released to be captured resulting in a much lower energy yield. Draft: in the theoretical results there were no drafts of air involved. Drafts are however in the experiment resulting in a decrease of the energy from the alcohol reaching the water as it was dissipated by the air resulting in a lower energy yield. ; Distance between spirit burner and beaker: the distance between the spirit burner and the beaker causes a greater portion of the energy to be dissipated into the environment before reaching the water in the beaker causing it result in a lower energy yield. ; Energy absorption: In the theoretical results all energy released goes into the water.
However in the experiment this is not practical as a percentage of heat will be absorbed by the beaker itself causing it to result in a lower energy yield. Through all the previous reasoning it is evident that they have a major effect on the energy yield reducing it from -2021 k/Mol to -kick] having a difference of kick]. Ways to prevent or minimize these problems are the following: ; Incomplete Combustion: this is the hardest to control as without access to specialized equipment it is hard to get enough oxygen quick enough at the reaction site in.
Possible ways to minimize this is burning it in an oxygen rich area (low altitudes) although this often impractical so all you can do Just expect incomplete combustion to occur. ; Heat Dispersion : this is relatively easy to minimize but almost impossible to prevent as combustion in a calorimeter is near impossible as oxygen is needed in a combustion reaction and a calorimeter prevents ample oxygen to be present in the reaction. Ways to minimize this would be to put a cylinder around the experiment.
This would increase the heat energy that goes up towards the beaker but might have an effect on the oxygen intake to the reaction site resulting in an incomplete combustion causing a low energy yield anyway. Draft : to control draft it helps to close all doors and turn off fans as this stills the air and slows down and minimizes the loss of energy due to drafts. ; Distance between spirit burner and Beaker: the easiest to minimize, as raising the spirit burner toward the beaker will allow more energy to be captured , minimizing energy loss in the process. Energy absorption: Not a lot can be done about this as the beaker needs to be able to be transfer heat quickly so it can be transferred to water. Validity This experiment is not valid to compare trends and make assumptions as every experiment was carried out in different circumstances . It could be made a valid experiment if all the variables were controlled except independent and dependent variables. This experiment when carried out correctly collects all the data required to perform all necessary calculations.
However the following data is less accurate due to will be inaccurate as the beaker will constantly be losing heat as soon as heat is added to it. Also the final recording of it could be askew as the temperature of the thermometer and the temperature of the water will be trying to reach equilibrium. The following trends I observed in the experiment carried out are: ; Experimentally ethanol appeared to be the most efficient fuel, burning at an average of 22% efficiency but was observed to in one experiment burn at a 25% efficiency.
Butane was the next most efficient at 20% efficiency , then proposal at 18. 5% efficiency and last was methanol at 17% efficiency. ; Experimentally Butane has the highest energy yield per a mole at jack/mol then Proposal at jack/mol. Ethanol was the next highest at jack/mol while methanol was last at jack/mol. ; Experimentally Butane had the highest energy per a gram of fuel tat. k/g with ethanol being the next highest at 6. Ski/g then Proposal was at 6. Ski/g while Methanol was at 3. Ski/g.