Determination of the Enthalpy Change of a Reaction :: GCSE Chemistry Coursework Investigation

Determination of the Enthalpy Change of a ReactionDetermine the enthalpy careen of the thermic decomposition of atomic number 20 carbonate by an indirect method based on Hess law.Determination of the Enthalpy Change of a ReactionDetermine the enthalpy change of the thermic decomposition of calciumcarbonate by an indirect method based on Hess law.Using the proposed method of obtaining results, these values weregatheredReaction 1 CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) graph in both cases represents the mean of the data.Using the equation for enthalpy change H = mcTWhere m = Mass of liquid to which fire up is transferred to (g)c = Specific heat capacity of aqueous solution (taken as water = 4.18J.g-1.K-1)T = Temperature change (oK)We can thus determine the enthalpy changes of reception 1 and reaction2 using the mean () of the data obtained.Reaction 1 H = 50 x 4.18 x -2.12H = -443.08This value is for 2.51g of calcium carbonate, not 100.1g which i s its molecular weight. thence H = -443.08 x (100.1 / 2.51) = -17670.2 J.mol-1.H = -17.67 kJ.mol-1.Reaction 2 H = 50 x 4.18 x -10.3H = -2152.7This value is for 1.37g of calcium oxide, not 56.1g which is itsrelative molecular mass.Therefore H = -2152.7 x (56.1 / 1.37) = -88150.7 J.mol-1.H = -88.15 kJ.mol-1.Hess law states that 1The total enthalpy change for a chemicalreaction is independent of the route by which the reaction takesplace, provided initial and final conditions are the same.This means that therefore the enthalpy change of a reaction can bemeasured by the advisement of 2 other reactions which relate directlyto the reactants used in the first reaction and provided the samereaction conditions are used, the results will not be affected.We watch the problem set by the experiment to determine the enthalpychange of the thermal decomposition of calcium carbonate. This isdifficult because we cannot accurately measure how much thermal energyis taken from the surroundings and pro vided via thermal energy from aBunsen flame into the reactants, due to its endothermic nature.Therefore using the enthalpy changes obtained in reaction 1 andreaction 2 we can set up a Hess cycleThus using Hess law we can calculate the enthalpy change of reaction3.Reaction 3 H = Reaction 1 - Reaction 2H = -17.67 - (-88.15) = +70.48 kJ.mol-1.Comparing the value +70.