Comparing The Enthalpy Change Of Combustion Of Different Alcohols :: GCSE Chemistry Coursework Investigation

Comparing The Enthalpy Change Of Combustion Of Different AlcoholsThe depend of my experiment is to investigate the enthalpy of combustionof a range of alcohols. The standard enthalpy of combustion is theenthalpy change that occurs when 1 mole of a arouse is burned completelyin oxygen under standard conditions 1 atmosphere pressure and 298K.All combustion reactions ar exothermic which is why I am expectingall the values for the enthalpy change of combustion to always benegative.Prediction==========I predict that the greater the number of carbon atoms in that location are in thealcohol molecule, the greater the enthalpy change of combustion itwill have. This is because in a chemical reaction energy is needed inorder to break bonds and energy is released when bonds are made. If Iwere to look at these two values the energy required to break thebonds of the reactants and the energy released when the bonds of theproduct are made then I am able to work go forth the enthalpy change ofc ombustion of the alcohol. In order to do this we need to have it away thebong enthalpies of the bonds in the process. The quantity of energyneeded to break a particular bond in a molecule is called the bondenthalpy. Below is a table containing the bond enthalpies of the bondsthat occur in the combustion of an alcohol.BondsWe use the average bond enthalpies as the exact value of a bondenthalpy depends on the particular compound in which the bond isfound. GRAPHDH1By looking at the equation for the reaction that occurs when analcohol burns, we realise that the reaction involves both time outbonds and making new ones. From the equation of the process we stubtell how many of the different number of bonds are broken and made andso work out the enthalpy change of combustion. We can work out theenthalpy of combustion of methanol by using the bond enthalpy valuesCH3OH + 1.5O2CO2 + 2H2OWe can use the enthalpy cycle above to work out the value for theenthalpy change of combustion of methanol, represented by DH1. Thecalculation is done as shown belowDH2 = enthalpy change when bonds are broken= 3 E(C-H) + 1 E(C-O) + 1 E(O-H) + 1.5 E(O=O)= 3(413) + 358 + 464 + 1.5(498)= 2808 kJ mol-1DH3 = enthalpy change when bonds are made