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Ch.6 - Thermochemistry
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.6 - ThermochemistryProblema 88
Capitolo 6, Problema 88

Use standard enthalpies of formation to calculate ΔH° for the reaction: C(s) + H2O(g) → CO(g) + H2(g).

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Identify the standard enthalpy of formation (ΔH_f°) for each substance involved in the reaction. Remember that the standard enthalpy of formation for any element in its standard state, such as C(s), is zero.
Write the balanced chemical equation for the reaction: C(s) + H2O(g) → CO(g) + H2(g).
Use the formula for calculating the standard enthalpy change of the reaction: ΔH° = Σ(ΔH_f° of products) - Σ(ΔH_f° of reactants).
Substitute the standard enthalpies of formation into the formula: ΔH° = [ΔH_f°(CO) + ΔH_f°(H2)] - [ΔH_f°(C) + ΔH_f°(H2O)].
Calculate the sum of the enthalpies of formation for the products and subtract the sum of the enthalpies of formation for the reactants to find ΔH° for the reaction.

Concetti chiave

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Standard Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial value used in thermodynamics to calculate the overall enthalpy change of a reaction. Each substance has a specific ΔH°f, which is typically found in tables and is measured under standard conditions (1 atm pressure and 25°C).
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Enthalpy of Formation

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken to achieve the reaction. This principle allows for the calculation of the enthalpy change of a reaction by summing the enthalpy changes of individual steps, making it possible to use standard enthalpies of formation to find ΔH° for complex reactions. It emphasizes the state function nature of enthalpy.
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Hess's Law

Enthalpy Change of a Reaction

The enthalpy change of a reaction (ΔH°) is the difference between the total enthalpy of the products and the total enthalpy of the reactants. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). By using the standard enthalpies of formation of the reactants and products, one can calculate ΔH° using the formula: ΔH° = ΣΔH°f(products) - ΣΔH°f(reactants).
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Enthalpy of Formation
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