Clarifying Standard Enthalpies of Formation and Standard Reaction Enthalpy

[Jack Amos 2I]

Does each molecule in a given reaction have a standard enthalpy of formation? Or is my understanding of the difference between standard reaction enthalpy and standard enthalpy of formation incorrect?

[905783577]

Each molecule does, however lone elements do not.

[Sujin Lim 1H]

Standard Enthalpy of Formation is the enthalpy change of a reaction (i.e. reaction enthalpy) for a chemical reaction done under standard conditions where one mole of a substance is formed from the most simple/stable elements that make up that substance. On the other hand Standard Reaction Enthalpy is just the reaction enthalpy for a chemical reaction done under standard conditions. The Standard Reaction Enthalpy value does not necessarily have to be for a chemical reaction where the products are formed from the most stable elements, but the standard enthalpy of formation does.

[Michelle_Duong_3H]

Hello,

Standard enthalpy of formation is the enthalpy change when 1 mole of substance is formed from its elements in their most stable forms. The standard enthalpy of formation for an element in its most stable form is equal to 0.

Standard reaction enthalpy is the enthalpy of a reaction when the reactants and products are in standard state. For a gas, this is at 1 atm and for a solution, this is 1 M. For both, the temperature is 25 degrees C. This does not necessarily mean that a compound is being formed from its elements.

Hope this helps!

[Mia Yamada 1J]

To calculate the standard enthalpy change of formation, take the sum of the standard enthalpies of formation of the products and subtract from it the sum of the standard enthalpies of formation of the reactants.