standard reaction enthalpy vs reaction enthalpy

[inlovewithchemistry]

is there a difference between standard reaction enthalpy and reaction enthalpy? I don't understand why you have to use Hess's Law for 4D15 but not for 4D17, and they use the different wording. thank you!

[Mona Lee 4L]

If reactants and products are at different states or reactions take place at different pressures, the enthalpy of the reaction can be different. Therefore, the standard reaction enthalpy refers to the enthalpy when all reactants and products are in their standard states at 1atm. Reaction enthalpy refers to the enthalpy of one specific reaction which may be different from the standard because of what I explained above.