Thermochemistry with Equation Stoichiometry
Key Questions
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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?
Questions
Thermochemistry
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Energy Change in Reactions
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Enthalpy
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Exothermic processes
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Specific Heat
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Calorimetry
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Thermochemistry of Phase Changes
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Thermochemistry with Equation Stoichiometry
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Hess' Law
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Spontaneous and Non-Spontaneous Processes
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Entropy
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Gibbs Free Energy
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Endothermic processes
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Born-Haber Cycle - Formation
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Born-Haber Cycle - Solution