Final answer:
A thermochemical equation links a reaction's stoichiometry to its enthalpy change, depicted as ΔHrxn, which represents the heat of reaction.
Step-by-step explanation:
A thermochemical equation links a reaction's stoichiometry to its enthalpy change or ΔHrxn. This ΔH value represents the heat of reaction, signifying the amount of heat either absorbed or released during the reaction, involving the number of moles of reactants and products as indicated in the chemical equation. For example, the combustion of methane can be represented by the thermochemical equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ΔH = -890.4 kJ, where the negative enthalpy change indicates an exothermic reaction in which the system releases heat.
The practice of using such equations often involves Hess's law, which outlines that the enthalpy change for a total process is equal to the sum of the enthalpy changes of its stepwise processes, due to enthalpy being a state function.
Enthalpy changes in chemical reactions are critical and are frequently measured using calorimetry, providing essential insights into the energy dynamics of chemical processes.