Or if there is little oxygen at all there can be pure carbon.
Hydrocarbon (fuel) + Insufficient Oxygen Carbon + Water
Complete combustion of Ethanol.
Ethanol + oxygen carbon dioxide + water.
C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l)
If the oxygen supply is restricted - meaning that there's not enough air - then the combustion of alkanes produces the poisonous gas carbon monoxide.(See equation showing the combustion of methane in a restricted supply of air)
COMPLETE COMBUSTION
Hydrocarbon (fuel) + Oxygen Carbon dioxide + Water
INCOMPLETE COMBUSTION
Hydrocarbon (fuel) + Insufficient Oxygen Carbon Monoxide + Water
Or if there is little oxygen at all there can be pure carbon.
Hydrocarbon (fuel) + Insufficient Oxygen Carbon + Water
The reaction involved in burning Hydrocarbons is Exothermic because heat is given out to its surroundings. The reaction’s energy is higher than that of the product. Exothermic reactions occur when the hydrocarbon takes energy in from its surroundings therefore the temperature increases. The energy is given out when forming the bonds between the new water and carbon dioxide molecules. The amount of energy produced by exothermic reactions can be calculated by using the solution calorimetry formula which uses temperature changes to work out energy changes. The calculation is:-
Mass of substance × rise in Temperature × SHC (specific heat capacity)
The specific heat capacity is the number of joules required to heat one gram of water by 1°C. I have chosen water because it the most easily available substance and is reliable and safe. The specific heat capacity for water is known to be 4.2.
Prediction: I predict that the more bonds there are holding the Carbon, Oxygen and Hydrogen atoms together; more energy will be required to break them down. The larger the molecule, more energy will be required to break its bonds, therefore more heat will be produced. This is because large molecules have many bonds, but small molecules have fewer bonds.
So the smaller molecules use up less energy trying to break down their bonds and will be able to release a bigger amount of energy producing heat. This is known as complete combustion. Where as the bigger molecules spend quite a lot of their energy trying to break up their bonds so will release less energy this is known as incomplete combustion. Paraffin has larger molecules than ethanol so I predict the burning of the paraffin will cause the greatest rise in temperature of the water.
Method:
To demonstrate the effect of complete and incomplete combustion a preliminary investigation
will be done by placing a glass beaker containing 100cm3 of water on a tripod and gauze. The starting temperature will be recorded. The Bunsen burner will be turned on to safety flame (low oxygen availability) and the change in temperature recorded at 1 minute intervals. The procedure will be repeated for the roaring flame (high oxygen) and a second set of results recorded. These will be tabulated and a graph plotted of temperature against time.
Things that I will keep constant throughout the investigation include:
Volume of water 100cm3
Type of beaker ((glass)
Surrounding temperature
Height of beaker from bunsen
Same set of scales
Same thermometer
The method I will use is as follows: Measure 100cm3 of water into a copper beaker. Place the copper beaker into the grasp of a clamp stand. Take the starting temperature of the water and gather a chosen fuel burner and weigh it on the scales with the lid off. Place the chosen fuel burner under the beaker and adjust the clamp if needs be until the flame is just touching the bottom of the beaker. Leave to heat up until the temperature of the water reaches 20°C more than the starting temperature of the water. Weigh the fuel burner and calculate the difference in weight as well as the change in temperature. Record all results.
Things that I will keep constant throughout the investigation include:
Volume of water 100cm3
Type of beaker (copper )
Surrounding temperature
Height of beaker from the wick
Same set of scales
Same temperature rise of 20 degrees
Same thermometer
Apparatus: Clamp, Stand, Copper Beaker, Fuel burner, Scales, Thermometer, Measuring cylinder, 100cm water, Paraffin, Ethanol.
Results:
Comparing complete combustion and incomplete combustion
Safety flame Energy produced Roaring flame Energy produced a change
a change in temperature of 36 degrees in temperature of 52 degrees in
in five minutes. five minutes.
The energy gained by the water was The energy gained by the water was
100×36×4.2=1512 Joules 100×52×4.2=21840 Joules
Here is a graph to show how effective combustion was in terms of temperature
The roaring flame caused a higher rise in temperature because the combustion was more complete.
Results for the efficiency of ethanol and paraffin as fuels
Energy produced
Ethanol 1st test 100×4.2×23=9660 Joules
Ethanol 2nd test 100×4.2×23=9660 Joules
Paraffin1st test 100×4.2×20=8400 Joules
Average=8190 Joules
Paraffin 2nd test 100×4.2×19=7980Joules
Energy per gram J/g = Joules per gram
Ethanol 1st test J/g 9660÷1.56=6192.3
Average=6359.65 J/g
Ethanol 2nd test J/g 9660÷1.48=6527
Paraffin1st test J/g 8400÷1.18=7118.6
Average=6884.3 J/g
Paraffin 2nd test J/g 7980÷1.2=6650
It appears that the paraffin caused the greatest rise in temperature and therefore must have released the bigger amount of energy when burned.
Evaluation
I believe my results were very inaccurate. Below is a list of reasons why it was an inaccurate experiment.
1. Energy given off through sound and light
2. Heat conducted and convected away through the air. 3. Radiation of heat out into the atmosphere. The beaker was made of copper which is a very good conductor of heat.
4. The fact that the beaker gets hot.
5. Heat may be take away through air currents.
6. The fact that at higher temperatures, heat is lost faster to the air and out of the beaker, due to the bigger heat difference, making the higher temperatures more inaccurate. 7 By incomplete combustion.
8. The availability of fuel for the wick to burn, if not enough then the wick would burn not the fuel which would give an inaccurate result.
9. Evaporation of water so there will be less water to heat, making the water hotter.
10. The size of the wick.
11 The water may not have been at the same temperature.
12. The flame size changed due to the type of fuel, hence it was a different distance away from the beaker each time. 13. Different burners were used for each of the fuels and these may have different efficiencies and wicks which would affect the rate of fuel burning.
14. The two different fuels may have had differing rates of evaporation.
The equipment that I used in this experiment was very inaccurate because heat is a bad way of transferring energy without any loss of it. I feel that the most limiting factor of the experiment is the convection of air and to a lesser extent, of water. Also during the experiment, some of the water will have evaporated, thus the water mass/temp reading will be altered.
I should have weighed the spirit burner with the lid on and not off to reduce the chance of evaporation of fuel.
I feel that this experiment could have been improved by using a wider range of fuels such as methanol and butanol. This would give a wider range of results to support a firm conclusion. Next time reducing heat lost would be my main priority. Improving insulation techniques would be useful in obtaining the most reliable data I could.
Another error is that of incomplete combustion. Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide (carbons atoms bond with two oxygen atoms).
If there is a limited supply of oxygen then you get carbon monoxide (each carbon atom can only bond with one oxygen atom). This is when incomplete combustion has occurred. This is so because the carbon monoxide could react some more to make carbon dioxide. If the oxygen supply is very limited then you get some atoms of carbon released before they can bond with any oxygen atoms. This is what we call soot. Since heat is given out when bonds form, less energy is given out by incomplete combustion. So this is why it affects the outcome of the experiment. To overcome this problem, I would have to make sure a sufficient supply of oxygen was involved in the reaction.
