Thermochemistry with Equation Stoichiometry

Key Questions

  • What is thermochemistry with equation stoichiometry?

    Answer:

    Consider an exothermic combustion reaction. The amount of heat may be treated as a stoichiometric product, precisely dependent on the amount of hydrocarbon combusted.

    Explanation:

    Methane combustion drives our civilization to a very great degree:

    CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O, DeltaH = -890 kJ mol^-1.

    The quoted enthalpy of combustion is per mole of reaction as written. You don't have to know these; you do have to know how to balance the equation. Because this energy is associated with the combustion of 1 mol of methane, I could also treat the evolved energy as a reagent or product in the reaction:

    i.e. CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O + 890 kJ.

    It would be on the reactant side if the reaction was endothermic. In other words the minus sign denotes evolution of heat. Alternatively, 890 kJ of heat are evolved from the above reaction, so I am treating energy as a product just as carbon dioxide and water are (as indeed it is; of course the heat is a consequence of the formation of water and carbon dioxide bonds). If less than 16 g (1 mol) methane are combusted, the heat evolved will diminish stoichiometrically. Does this address your question?

    anor277 · 1 · Oct 5 2015

Questions

Thermochemistry