Standard Reaction Enthalpies

[Chelsea Culi 3F]

I'm not quite sure I understand the difference between the standard reaction enthalpy (delta H) and the standard enthalpy of formation (delta Hf). How do we know when we are dealing with delta H or delta Hf?

[Mona Reddy Kurra 1J]

Hi! Standard reaction enthalpy (ΔH°) refers to reactions where all reactants and products are in their standard states at 1 atm while standard enthalpy of formation (ΔHf°) deals with formation of one mole of a substance from the elements in their most stable form. I think the key difference in the two is that standard enthalpy of formation is attributed to one mole of the substance. Because of this, standard enthalpies of formation can be used to determine the standard reaction enthalpy through the formula ΔH°= ∑ΔHf°(P) - ΔHf°(R). Standard enthalpies of formation can be calculated for a certain compound when given the standard reaction enthalpy through molar ratios. I hope that helps!

[905695298]

I think standard enthalpy of formation is the change of enthalpy in the formation of one mole of the compound from its element, while the standard enthalpy of reaction is the change of enthalpy when one mole of the compound is transformed by the chemical reaction. So I think the key difference is that one is the formation from element to compound and one is during the reaction of the compound.

[Lauren Brotman 2F]

Standard enthalpy of formation is specifically the enthalpy for the formation of 1 mole of a substance from its elements in their most standard forms. Standard reaction enthalpy is the change in enthalpy for a whole reaction under standard conditions. You can also use standard enthalpy of formation to calculate standard reaction enthalpy.