A-LevelChemistryChemical energeticsOct/Nov 2015Paper 1 Q61 Mark
Hess' law may be used to determine enthalpy changes using average bond energies, as shown in the diagram. [Figure showing U, V, W for reactants, products, isolated gaseous atoms] U is the sum of the average bond energies of the reactants, and V is the sum of the average bond energies of the products. For the reaction shown below, which expression will give a value for W, the enthalpy change of combustion of methane? CH4 + 2O2 → CO2 + 2H2O
AU – V
BU + V
C2(U – V)
DV – U
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The correct answer is A. This question tests the candidate's understanding of chemical energetics within the Chemistrysyllabus. The examiner's mark scheme requires...
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