Stoichiometry of Thermochemical Equations

A thermochemical equation is a balanced equation that includes the heat of reaction (Af/rxn)- Keep in mind that the A//,xn value shown refers to the amounts (moles) of substances and their states of matter in that specific equation. The enthalpy change of any process has two aspects  

The sign of A// depends on whether the reaction is exothermic (-) or endothermic (-h). A forward reaction has the opposite sign of the reverse reaction. 

Magnitude. The magnitude of AH is proportional to the amount of substance reacting. 

Formation of 1 mol of water from its elements (half the amount in the preceding equation)  

Note that, in thermochemical equations, we often use fractional coefficients to specify the magnitude of A//,xn for a particular amount of substance. Moreover, in a particular reaction, a certain amount of substance is thermochemically equivalent to a certain quantity of energy. In the reaction just shown, 

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Second, these equations take into account, besides temperature, a variety of factors affecting the decomposition kinetics, such as the composition, stoichiometry, and thermochemical characteristics of the reaction, the pressure of the excess gaseous products and of the foreign (inert) gas in the reactor, and even, physical properties of the reactant (the size of particles, molar mass, and density). 

The thermochemical equation for this reaction is shown above. This equation provides a link to convert the amount of NO formed to the energy absorbed. As in any other stoichiometry problem, we will work with moles of substance, which we can obtain from the given mass. Note that the stated AH° value is for the production of two moles of NO because two moles appear in the equation. 

Energy and Its Units Heat of Reaction Enthalpy and Enthalpy Change Thermochemical Equations Applying Stoichiometry to Heats of Reaction... 

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