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Thermochemical equations are just like other balanced equationsexcept they also specify the heat flow for the reaction. The heat flow is listed to the right of the equation using the symbol ΔH. The most common units are kilojoules, kJ. Here are two thermochemical equations: H 2 (g) + ½ O 2 (g) → H 2 O (l); ΔH = -285.8 kJ HgO (s) → Hg (l) + ½ O 2 (g); ΔH = +90.7 kJ When you write thermochemical equations, be sure to keep the following points in mind: Coefficients refer to the number of moles. Thus, for the first equation, -282.8 kJ is the ΔH when 1 mol of H 2 O (l) is formed from 1 mol H 2 (g) and ½ mol O 2 . Enthalpy changes for a phase change, so the enthalpy of a substance depends on whether is it is a solid, liquid, or gas. Be sure to specify the phase of the reactants and products using (s), (l), or (g) and be sure to look up the correct ΔH from heat of formation tables. The symbol (aq) is used for species in water (aqueous)...
