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Hess' law cycles-Standard enthalpy changes

I am going over Hess' law cycles and I can't seem to remember why standard enthalpy change of formation always needs 1 mole of product on the right hand side and why combustion always has 1 mole of elements and compounds on the left side of the equation.

All I know is that it does! But whyyy?

Thanks
Reply 1
To do it in a standard way.
Reply 2
Formation is forming products- chemists need a way to calculate enthalpy change keeping most things constant so they calculate for 1 mol of products formed.

Combustion is reacting 1 mol of o2 and reactants.

Basically its all to do it in a standard way.
Reply 3
Original post by ETRC
Formation is forming products- chemists need a way to calculate enthalpy change keeping most things constant so they calculate for 1 mol of products formed.

Combustion is reacting 1 mol of o2 and reactants.

Basically its all to do it in a standard way.


It is 1 mol of substance with as many mol of O2 as required for complete combustion.
Reply 4
By definition - "The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy from the formation of 1 mole of the compound from its constituent elements, with all substances in their standard states at 1 atmosphere."
Reply 5
Original post by Pigster
It is 1 mol of substance with as many mol of O2 as required for complete combustion.


oh yeah i worded it wrong, i was typing quickly

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