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## Main Question or Discussion Point

Hi, I'm trying to understand why the Hess's law process which resembles addition of equations is used as opposed to other methods, such as the sum of the products minus sum of reactants formula:

ΔH°rxn = Σ ΔH°f (products) minus Σ ΔH°f (reactants)

I get how its for instances such as rust or diamond formation where a laboratory could not replicate the process conveniently, but couldn't you also use the formula in those cases, too?

Elementary books often have questions like "verify an equation addition process with the formula", but why in practice could you only use one or the other? Wouldn't you be using all the same information either way (moles and enthalpies of formation)?

Thanks.

ΔH°rxn = Σ ΔH°f (products) minus Σ ΔH°f (reactants)

I get how its for instances such as rust or diamond formation where a laboratory could not replicate the process conveniently, but couldn't you also use the formula in those cases, too?

Elementary books often have questions like "verify an equation addition process with the formula", but why in practice could you only use one or the other? Wouldn't you be using all the same information either way (moles and enthalpies of formation)?

Thanks.