During chemical reactions, energy is either released or absorbed, normally as either heat or light energy. There are two types of reactions that involve heat, exothermic reactions and endothermic reactions. In an exothermic reaction heat energy is released and increases the temperature of its surroundings. Conversely in an endothermic reaction heat energy is absorbed and the surrounding temperature decreases. The measurement of change in heat is called calorimetry.
The change in heat energy is known as the enthalpy change , and it is the quantity of heat released or absorbed during a reaction when 1.00 mol of a substance undergoes a chemical reaction while under constant pressure. The molar enthalpy of Combustion is the quantity of heat energy released when 1.00 mol of a substance is completely burnt in excess oxygen while under constant pressure (Liu & Lum n.d.).
This investigation tests the relationship between the Molar mass of several different alcohols against the molar enthalpy of combustion. The five alcohols being investigated are Ethanol (CH3CH2OH), Propanol (CH3 (CH2)2OH), Butanol (CH3 (CH2)3OH), Pentanol (CH3 (CH2)4OH), and Hexanol (CH3 (CH2)5OH). Each of these alcohols will be used in a combustion reaction to heat 100ml of water by 10OC. The mass of alcohol used by the reaction during that time will be recorded and the enthalpy will then be calculated.
The equations for the five reactions are listed below.
Hexanol: (Neutrium 2014)
Hypothesis: If alcohols with different molar masses are used to heat water, then the enthalpy of combustion will be greater for alcohols with a larger molar mass.
Independent Variable: The molar mass of alcohols
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...e effect of the errors listed above have altered the data readings. The percentage error calculations indicate that the experimental values were all approximately one-tenth of the literary values. As this appears to be consistent, it suggests that a systematic error was affecting the data, with heat loss appearing to be responsible.
The hypothesis “If alcohols with different molar masses are used to heat water, then the enthalpy of combustion will be greater for alcohols with a larger molar mass” was supported by the results of this investigation.
Liu, D & Lum, F n.d., Core Knowledge Chemistry Subject Guide, 7th edn, FresnelCK, Adelaide.
Neutrium 2014, HEAT OF COMBUSTION, Neutrium, accessed 10 June 2015, .
Stretton, T n.d., Organic Compounds: Physical and Thermochemical Data, Upper Canada District School Board, accessed 9 June 2015, .
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