The reactants' total Standard Enthalpy of Formation,`DeltaH_f^0`, is a component of the Standard Enthalpy of Reaction, `DeltaH_r^0`, along with the products' total Standard Enthalpy of Formation.

Reactants' Standard Enthalpy of Formations `(DeltaH_f^0)` = `sum_"reactants" v_i * (DeltaH_f^0)_i` .

• `v_i` - stoichiometric coefficient for `"reactant"_i`
• `(DeltaH_f^0)_i` - Standard Enthalpy of Formation for `"reactant"_i`

This equation allows you to sum Standard Enthalpy of Formation for up to ten reactants.  

Notes

Enthalpy, H, of the system is equal to the internal energy of the system, U,  plus the product of pressure and volume of the system, PV.  The enthalpy of a homogeneous systems is proportional to the size of the system. For various molecular substances the specific enthalpy can be specified as H/m, where M is mass.

The Standard Enthalpy of Reaction is the enthalpy change (change in chemical potential energy of the system) that occurs when one mole of matter undergoes a chemical reaction under standard conditions.  The Standard Enthalpy of Reaction is typically measured in units of kJ/mole. Likewise the Standard Enthalpy of a Formation is also measured typically in kJ/mole.

The Standard Enthalpies of a Formation, `DeltaH_f^0`, are computed under standard conditions that include:

• standard temperature - 25 degrees C
• standard pressure (for gases) - 1 atmosphere
• standard Molar concentration (for solute in an ideal solution) - 1 M
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