Hess's Law

[Maegan Abutin 2C]

Hi. Can someone please explain limitations of Hess's Law and where it might not be applicable/acurrate in finding enthalpy changes?

[405981594]

Hess's law does not apply when enthalpy changes are not additive, when the reaction is additive, when energy is exchanged with the surroundings in another form other than heat.

[605988349]

The limitations for Hess'a Law is that it's not valid for reactions that involved significant changes in temperature, that is because the enthalpy of a reaction is temperature dependent. Also, if there are drastic changes to the pressure between reaction, all these limitations should be taken into considering since it would not be applicable in using Hess' s Law.

[405963118]

There is also potential energy or heat lost when the reactions take place. Hess's law assumes none of this happens. It neglects environmental factors which are necessary to finding the true values of energy.