Question: how is the standard enthalpy of reaction calculated?
Answer: The standard enthalpy of reaction, ΔH⊖rxn Δ H r x n ⊖ , can be calculated by summing the standard enthalpies of formation of the reactants and subtracting the value from the sum of the standard enthalpies of formation of the products. ... The enthalpy of reaction is calculated under standard conditions (STP).