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Combustion of Alcohols

Extracts from this document...

Introduction

Combustion of Alcohols

Background information

The breaking of bonds is endothermic, and the making of bonds is exothermic. The difference between the two decides whether a reaction is exothermic or endothermic. We can calculate the theoretical change in energy, by using given values, of the energy required to break certain bonds.

Chemical Bond Energy (KJ/Mol) Chemical Bond Energy (KJ/Mol)

C-H 413 O--O 497

O-H 464 C--O 745

C-O 358 C-C 346

1 cm3 of water = 1g of water

Heat Transferred = Mass of Water X Temperature Rise X 4.2

(In KJ) (in Kg) (in oC)

Variables

Type of Alcohol (Independent Variable),

Container size/Volume of water,

Type of container,

The amount of carbon soot left on the container,

Volume/Mass of alcohol,

Time,

Distance between wick and container,

Tripod & gauze over stand, boss & clamp,

Starting temperature of water.

Fair Test:

Type of Alcohol (Independent Variable): This variable has to be the same type of alcohol, i.e. Propan-1ol , because with every carbon added in the chain after Methane, there is another place in the chain for the O-H bond to go in, or the possibility of another one added in. If the mentioned were changed, then the way and the amount of burning the chain does, changes. If the chain length was varied, then the amount of burning the chain does, changes. Note that for every one carbon added to the chain, H2 is added as well.

Container size: The container size affects the volume of water inside it, I can't put 300cm3 of water inside a 200cm3 container. Also, if the volume of water I find most appropriate, only fills half the container, then the space not being used (and/or the larger the surface area of the water to air)

Middle

Safety: Keep lid on burners at all times, when moving and not burning. This is to prevent evaporation and the possibility of an explosion. Keep fingers, clothes and any other body parts away from burners to prevent burns.

Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 0 346 0 C-O 2 745 1490

C-H 3 413 1239 O-H 4 464 1856

C-O 1 358 358

O-H 1 464 464

O--O 1.5 497 745.5

Total 2806.5 - 3346 = -539.5

Equation: CH3OH + 1.5O2 = CO2 + 2H2O - 539.5J

Ethanol Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 1 346 346 C-O 4 745 2980

C-H 5 413 2065 O-H 6 464 2784

C-O 1 358 358

O-H 1 464 464

O--O 3 497 1491

Total 4724 - 5764 = -1040

Equation: C2H5OH + 3O2 = 2CO2 + 3H2O - 1040J

Propan-1ol Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 2 346 692 C-O 6 745 4470

C-H 7 413 2891 O-H 8 464 3712

C-O 1 358 358

O-H 1 464 464

O--O 4.5 497 2236.5

Total 6641.5 - 8182 = -1540.5

Equation: C3H7OH + 4.5O2 = 3CO2 + 4H2O - 1540.5J

Butan-1ol Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 3 346 1038 C-O 8 745 5960

C-H 9 413 3717 O-H 10 464 4640

C-O 1 358 358

O-H 1 464 464

O--O 6 497 2982

Total 8559 - 10600 = -2041

Equation: C4H9OH + 6O2 = 4CO2 + 5H2O - 2041J

Pentan-1ol Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 4 346 1384 C-O 10 745 7450

C-H 11 413 4543 O-H 12 464 5568

C-O 1 358 358

O-H 1 464 464

O--O 7.5 497 3727.5

Total 10476.5 - 13018 = -2541.5

Equation: C5H11OH + 7.5O2 = 5CO2 +6H2O - 2541J

Hexan-1ol Numbers Of Bonds 1 Bond Energy Total Bond Energy Bond Type Numbers Of Bonds 1 Bond Energy Total Bond Energy

C-C 5 346 1730 C-O 12 745 8940

C-H 13 413 5369 O-H 14 464 6496

C-O 1 358 358

O-H 1 464 464

O--O 9 497 4473

Total 12394 - 15436 = -3042

Equation: C6H13OH + 9O2 = 6CO2 +7H2O - 3042J

Prediction: The tables below show the theoretical calculation of the energy released during the combustion of alcohol.

Conclusion

Correction of 11-12: I could seal the calorimeter, and move all the wicks to the same height.

Limitations of apparatus

The apparatus in this experiment is very bad, because heat is a bad way to transfer energy, without any loss of it. Any molecule, of any thing will conduct heat to a greater or lesser extent, radiation happens and can be reduced but not stopped, and the most limiting factor of this experiment is the convection of air, and to a lesser extent of water. In all the transfers of heat through the apparatus, you are giving energy to things other than the water. The wick, air, calorimeter, thermometer, burner, the not combusted alcohol clamp, boss and stand, are all given energy that, ideally should go to the water and be kept by it. During the experiment, some water will evaporate, and so your temperature/water mass readings will change because of this, your temperature reading might go up a little bit.

All the above paragraph with the exception of the last sentence, would decrease the readings.

Validity

Not every value of the test variable was tested, and the ones I did do need to be repeated to get better-backed results. Specifically Methanol, Butan-1ol and Hexan-1ol. This experiment would be improved if we could have used pure ethanol (drinking alcohol) apposed to methylated spirits, and perhaps if a wider range of alcohols was tested, then a better graph and graph could have been attained. Perhaps if I started the experiment below room temperature, so that the amount of gained energy, from room temperature, might equal the energy lost at temperatures higher than room temperature, then the experiment could produce better results. Another way to reduce heat loss from the water, is to use a Nutfield calorimeter, as shown on the following page, also using a bomb calorimeter is also feasible, shown on the next page.

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