Alcohol Combustion

Topics: Measurement, Carbon dioxide, Thermodynamics Pages: 5 (1553 words) Published: August 16, 2012
To find out difference in the heat of combustion for different types of alcohols.

The higher the number of carbon atoms in an alcohol is, the higher the energy for the heat of combustion. Alcohol is a homologous series, a series of organic compounds with similar formula and chemical properties, and increase in molecular size and mass. When the equations for combustion of these alcohols are listed in the order of increasing number of carbon atoms, Methanol 1 CH3OH(l) + 3/2 O2(g) ⋄ 1 CO2(g) + 2 H2O(l)

Ethanol 1 C2H5OH(l) + 3 O2(g) ⋄ 2 CO2(g) + 3 H2O(l)
Propanol 1 C3H7OH(l) + 9/2 O2(g) ⋄ 3 CO2(g) + 4 H2O(l)
Butanol 1 C4H9OH(l) + 6 O2(g) ⋄ 4 CO2(g) + 5 H2O(l)
Pentanol 1 C5H11OH(l) + 15/2 O2(g) ⋄ 5 CO2(g) + 6 H2O(l) The number of CO2 molecule increases in a linear fashion, as well as H2O. In the formation of carbon dioxide, C=O bonds are formed, releasing 1486 kJ per mol[i] in each molecule. As the coefficient for carbon dioxide is the same as the number of carbon atoms in the alcohol, the coefficient increases linearly in the increase in the homologous series of alcohol. The energy for combustion increases in the order of methanol ⋄ ethanol ⋄ propanol ⋄ butanol ⋄ pentanol (and that in linear fashion) because the increase in the number of molecules of carbon dioxide means that more energy must be released for the formation of the C=O bond.

5 spirit lamps for methanol, ethanol, propanol, butanol, and pentanol. Water
100ml beakers
Stop watch
Retort stand
Ceramic tile

Method and Variables
Pour 50ml of water into a beaker.
Place the beaker in the clamp connected to the retort stand on a ceramic tile. Measure and record the mass of lamp and the temperature of the water. Heat the beaker for 1 minute.
Measure and record the final mass of lamp and the temperature of water. Repeat step 1-5 for 3 more times.
Repeat the experiment with different types of alcohols.

Type of alcohol will be changed each time as independent variable, whereas for the dependent variable the heat of combustion will be measured. Other variables that should be kept under constant condition will be the height from the lamp to the beaker, equipments (thermometer, beakers, cylinder, etc.), room temperature, etc.

Table 1. Table to Show the Initial and Final Mass of Lamp and the Temperature of Water Before and After the Combustion | | |Trial 2 | |Trial 3 | |Trial 4 | |Trial 2 | |Trial 3 |

Trial 4 |ΔH Heat of Combustion (KJmol-1) |146.67 |270.39 |440.59 |648.57 |836.00 | | |Percentage Uncertainty (%) |20.51 |29.47 |21.79 |22.84 |30.09 | | |Absolute Uncertainty (KJmol-1) |±30.08 |±79.68 |±96.00 |±148.13 |±251.55 | |

Table 3. The Literature Values of Heat of Combustion for Different Types of Alcohol[ii] Alcohol |Methanol |Ethanol |Propanol |Butanol |Pentanol | |Literature Value of Heat of Combustion (KJmol-1) |-715 |-1371 |-2010 |-2673 |(no data) | |




Qualitative Data:
After boiling for a while, the bottom of the beakers that was directly exposed to the heat started to get covered by soot. The amount of the soot seemed to be more when alcohol with more carbons was used, but the actual...
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