Lab Report: Enthalpy Of Combustion Of Butanol Research Paper

1. Introduction The meaning of enthalpy of combustion is defined as “under standard condition”, how the energy will change when a substance contains 1 mole and burns in excess oxygen. In this experiment, alcohol (butanol) is used for burning. Alcohols are organic compounds containing Oxygen, Hydrogen and Carbon. They are a family of hydrocarbons that contain the -OH group. In this experiment butanol compounds by oxygen in air to form CO2 if there is a sufficient amount of oxygen. Alcohol is used and its formula of butanol is C4H90H.Combustion is principally the oxidation of cae hydrogen in a compound forms H20. Combustion produces heat as well as carbon dioxide and water (Kenneth,2005)…. Butanol + oxygen = carbon dioxide & water C4H9OH(aq) +602(g) → 4CO2(g)+5H20(aq)

1.Introduction Definition o Background/scientific theory to the topic (inc. any laws or equations you may be using) O Statement about the topic to be investigated Why the work was carried out Brief statement of the general method of approach to the problem Need academic references in this section – citations!!! 2. Aim The aim of this report is to determine the enthalpy of combustion of a sample of butanol and compare the result to the accepted value. 3. Method and materials 3.1 Method To begin with , 100cm3 of water was carefully put in a baker and it was placed on the tripod stand. Secondly, the temperature of the water was taken. After the temperature was taken, the draught shield was put around the tripod stand. Next, the spirit burner and butanol was weighed and they were placed under the tripod stand. After that, the burner was lit and it was burned for 5 minutes. Lastly, the final temperature of the water and the final weight of the burner were measured. 3.2 Materials 100cm3 of water Beaker Tripod stand Thermometer Draught shield Balance

Spirit Burner 4. Results Table 1: Results of water temperature Initial temperature of water оС. Final temperature of water °C Total change of temperature of water °C Methanol 22 55 33 Ethanol 22 55 33 Propanol 26 59 33 Butanol 26 59 33 Table 2: Results of burner mass

Initial mass of burner Final mass of burner Total change of mass of burner Methanol 85.6 81.8 3.8 Ethanol 85.6 63.9 21.7 Propanol 83.1 80.9 2.2 Butanol 83.1 81.1 5. Discussion

The data was collected and analyzed for each alcohol as given below: Methanol: Before Heating: Mass of spirit lamp = 46.2 g Mass of spirit lamp with methanol = 85.6 g Mass of methanol = 85.6 g – 46.2 g = 39.4 g Volume of Water = 100 cm3 Mass of Water (m) = Volume x Density = 100 cm3 x 1g/cm3 = 100 g Initial Temperature = 22°C After Heating: Final Temperature = 55 °C Temperature Change (AT) = Final Temperature – Initial Temperature = 55 °C – 22°C = 33 °C Temperature Change (AT) = 33 K Mass of spirit lamp and Methanol = 81.8 g Mass of Methanol burnt = 85.6 g -81.8 g = 3.8 g Molar Mass of Methanol = (12.01) + (4 x 1.01) + (16) = 32.05 g/ mol 13 | Moles of Methanol burnt = Mass of Methanol Molar Mass of Methanol = 3.8 g 32.05 g/mol = 0.1186 mol Specific Heat Capacity of Water = 4.18 Jg-1 K-1 Enthalpy Change during combustion = Mass of Water x Specific Heat Capacity x Temperature Rise of Water Enthalpy Change during combustion (AH) = mcAT = 100 g x 4.18]g-1 K-1 x 33 K = 13794) = 13.794 kJ Standard Enthalpy of Combustion of Methanol (AH°comb) = Enthalpy Change during combustion (AH) Number of Moles of Methanol = 13.794 kJ 0.1186 mol = 116.3 kJ/ mol Number of Carbon atoms in methanol = 1 From the following experimental data, it can be calculated that the standard enthalpy of combustion of methanol (AH°comb) is 116.3 kJ/mol.

Similar procedures are followed to determine the standard enthalpy of combustion of the rest of the alcohols. The results are tabulated in the table 3 Thus, all the 4 alcohols have been tested for their standard enthalpy of combustions. The overall results are as shown in a tabular form below: Table 3: The Standard Enthalpy of combustion of alcohol No. Alcohol Number of carbon Atom Standard Enthalpy of Combustion (AH °comb) (kJ/mol) Methanol -116.3 Ethanol 2 -254.3 propanol -376.9 4. butanol 4. -625.3

The above table of results can also be explained graphically. The graph relating the number of carbon atoms in an alcohol and its Standard Enthalpy of Combustion is shown below: Number of carbon atoms in an alcohol vs. Standard Enthalpy of Combustion AH°comb Bbb Figure 3. No. of Carbon Atom Vs Standard Enthalpy of Combustion The graph represents the trend in the experimental results. As the number of Carbon atoms in an alcohol molecule increases, the following standard enthalpy of combustion also increases.

The blue dotted line is the best fit line. The best fit line is a linear line. As a result, it can be concluded that the standard enthalpy of combustion of alcohols is proportionate to the number of carbon atoms the alcohol chain contains. 1 Error 1) Around 90% of the heat from the spirit lamp did not reach the base of the tripod stand itself. This was the main reason of error. Heat was lost very easily. A lot of heat was lost in this manner and contributed to a lower than expected temperature change in the water. This was undoubtedly, the main source of experimental error. 2)The mass of water might not have been constant throughout the heating process. Some of the water might have evaporated off, suggesting a mass loss. This would then give different results.

3) It was observed that during the combustion of alcohols, a yellow flame was obtained at times. This is the sign of the incomplete combustion of alcohols. As a result, carbon monoxide is formed instead of carbon dioxide. Therefore, this incomplete combustion results in low standard enthalpy of combustion values as the reaction is not complete. These sources of error could have been prevented at the first place. The random errors can be prevented in that manner. However, the systematic errors need to be corrected as well. Therefore, the method of the experiment can be evaluated further.

1) This experiment could have been carried out at a place of constant temperature 2) The calorimeter could have been insulated more. A thick cotton wool could have been added. 3)Minimize the heat lost by ensuring no gas (vapour) is lost during the heating process, by adding more cotton for insulation or covering the calorimeter with a thick lid. Conclusion The experiments carried out were quite successful, and yielded valid results. It has helped determine the relationship between the number of carbon atoms in an alcohol chain and its respective standard enthalpy change of combustion. The final results of the experiment are given as follows:

Thus, the hypothesis has been proved correct. As the number of carbon atoms in an alcohol chain increases, its respective standard enthalpy change of combustion also increases. As it can be seen, the standard enthalpy combustion values increase as the number of carbon atoms increase. This can be explained by each successive member of the series contains one more methylene group (-CH2-) than the previous one. When it is burnt, there will be one extra C-C bond and two extra C-H bonds to be broken. Therefore, much more energy is required for combustion. This is proven by the readings obtained in the table above.