The standard enthalpy change for the combustion of 1 mole of ethylene is -1303.1 kJ
C2H4(g) + 3 O2(g) ----> 2 CO2(g) + 2 H2O
Calculate the change of Hf for ethylene based on the following standard molar enthalpies of formation.
molecules Change in Hf (kJ/mol)
CO2 -393.5
H2O -241.8
Given,
delta H (combustion) = -1303.1 kJ for the reaction,
C2H4(g) + 3 O2(g) ----> 2 CO2(g) + 2 H2O
delta H (combustion) = delta H (products) - delta H (reactants)
delta H (products) = 2 x delta H (CO2) + 2 x delta H (H2O)
=> delta H (products) = 2 x (-393.5) + 2 x (-241.8) = -1270.6 kJ
delta H (reactants) = delta H (C2H4) + 3 x delta H (O2)
=> delta H (reactants) = delta H (C2H4) + 3 x 0 = delta H (C2H4)
(delta H (O2) = 0)
delta H (combustion) = delta H (products) - delta H (reactants)
=> -1303.1 = -1270.6 - delta H (C2H4)
=> delta H (C2H4) = 32.5 kJ
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