Experiment to Compare the Enthalpy Changes of Combustion of Different Alcohols :: GCSE Chemistry Coursework Investigation

Experiment to Compare the enthalpy Changes of Combustion of Different AlcoholsIntroduction This plan will try to pop outline how the experiment ofcomparing changes of electrocution of different alcohols will beconducted and what results are expected.BackgroundWhen chemical substance reactions take direct they are often accompanied byenergy changes.Chemical reactions virtually frequently occur in open vessels. That is,they take place at uninterrupted pressure. henry refers to energy atconstant pressure (volume may vary).EnthalpyAn example is best to illustrate to show enthalpy works. Methane -how much energy does its wallcules contain? The first thing needed isthe amount of methane present = 1 mole (16 g). What ever its value,the total amount of energy in a given amount of a substance (sometimescalled the Heat energy content) is known as the enthalpy, denoted H.Methane is a fuel to get energy from it, react it with oxygen.CH4(g) + 2O2(g) CO2(g) + 2H2O(l)The above chemical equa tion shows that 2 moles (64 g) of oxygenmolecules are required to burn 1 mole of methane. Again, it is unrealistic to know the total enthalpy (heat energy content) of theoxygen. Likewise, we cant know the total heat energy content of 1mole of CO2 and 2 moles of H2O (the products).Enthalpy ChangeH = (HCO2 + 2HH2O) - (HCH4 + 2HO2)In general,H = Hproducts - HreactantsBut remember, this is theoretical it is not possible to determine theabsolute value of the enthalpy of a chemical part or compound.However, H values for chemical reactions can be obtained. They can bemeasured experimentally, or calculated using Hesss Law (see later),or worked out in other ways.Exothermic and Endothermic ReactionsWhen chemical reactions take place they are often accompanied by heatchanges. The system (the reactants which form products) may give outheat to the surroundings, causing them to warm up. In this case thereactants have more stored energy (greater total enthalpy) than theproducts. Such chemical rea ctions are express to be exothermic. Thesystem may take heat from the surroundings, causing them to cool down.In this case the reactants have less stored energy (less totalenthalpy) than the products. Such chemical reactions are said to beendothermic.Exothermic reactions give out energy to the surroundings.Endothermic reactions take energy from the surroundings.Most reactions take place at constant pressure...It is possible to measure changes in heat energy that accompanychemical reactions. Most reactions take place in vessels that are opento the atmosphere, that is, they take place at constant pressure(volume may vary). The special name given to a change in heat energycontent measured at constant pressure is enthalpy change.