Determination of Enthalpy Change of a Reaction from Enthalpies of Combustion using Hess's Law

For the formation of butane from its elements in their standard states,4C(s) + 5H₂(g) → C₄H₁₀(g)The enthalpy of formation of butane would be impossible to measure because carbon and hydrogen form so many compounds alongside butane.The enthalpy of formation can be determined from the enthalpies of combustion of the reactants and products.4C(s) + 5H₂(g) → C₄H₁₀(g)
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      4CO₂ + 5H₂OΔH_f butane = 4 x ΔH_c carbon + 5 x ΔH_c hydrogen- ΔH_c butane