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Thermochemical Equation Thermochemical equations are chemical reaction equations with the enthalpy of reaction (∆Hrxn) written directly after the equation. Example of a thermochemical equation 2 H2 (g) + O2 (g)→ 2 H2O (l) ∆Hrxn = -571.6 kJ The negative value for ∆Hrxn is telling you that heat is lost to the surrounding Also that the equation is exothermic Rules for manipulating thermochemical equations If the thermochemical equation is multiplied by some factor, the value of ∆H for the new equation is equal to the ∆H in the original equation multiplied by that factor If the chemical equation is reversed, the sign of ∆H must be reversed Example, if you were to reverse the direction of the equation mentioned above you would get: 2 H2O (l)→ 2 H2 (g) + O2 (g) ∆Hrxn = +571.6 kJ...