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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Brown 15th EditionCh.5 - Thermochemistry문제 64
5장, 문제 64

From the enthalpies of reaction 2 C(s) + O2(g) → 2 CO(g) ΔH = -221.0 kJ 2 C(s) + O2(g) + 4 H2(g) → 2 CH3OH(g) ΔH = -402.4 kJ Calculate ΔH for the reaction CO(g) + 2 H2(g) → CH3OH(g)

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1
Identify the target reaction: CO(g) + 2 H_2(g) → CH_3OH(g).
Use Hess's Law, which states that the total enthalpy change for a reaction is the same, no matter how many steps the reaction is carried out in.
Write the given reactions and their enthalpy changes: 1) 2 C(s) + O_2(g) → 2 CO(g), ΔH = -221.0 kJ; 2) 2 C(s) + O_2(g) + 4 H_2(g) → 2 CH_3OH(g), ΔH = -402.4 kJ.
Manipulate the given reactions to derive the target reaction. Divide both given reactions by 2 to match the stoichiometry of the target reaction.
Subtract the enthalpy of the first reaction from the second to find the enthalpy change for the target reaction.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Enthalpy of Reaction

Enthalpy of reaction (ΔH) is the heat change associated with a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). Understanding ΔH is crucial for predicting the energy changes during reactions and for applying Hess's law to calculate unknown enthalpies.
추천 영상:
가이드 코스
02:34
Enthalpy of Formation

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps, regardless of the pathway taken. This principle allows chemists to calculate the enthalpy change for a reaction that may be difficult to measure directly by using known enthalpy changes of related reactions.
추천 영상:
가이드 코스
02:03
Hess's Law

Stoichiometry in Reactions

Stoichiometry involves the quantitative relationships between the reactants and products in a chemical reaction. It is essential for balancing chemical equations and determining the amounts of substances consumed or produced. In this context, stoichiometry helps in relating the enthalpy changes of the given reactions to find the ΔH for the target reaction.
추천 영상:
가이드 코스
01:16
Stoichiometry Concept
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Given the data N2(g) + O2(g) → 2 NO(g) ΔH = +180.7 kJ 2 NO(g) + O2(g) → 2 NO2(g) ΔH = -113.1 kJ 2 N2O(g) → 2 N2(g) + O2(g) ΔH = -163.2 kJ use Hess's law to calculate ΔH for the reaction N2O(g) + NO2(g) → 3 NO(g)

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교과서 질문

Consider the following hypothetical reactions: A → B ΔH = +30 kJ B → C ΔH = +60 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.

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We can use Hess's law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethane: 2 CH4(g) → C2H6(g) + H2(g) Calculate the ΔH° for this reaction using the following thermochemical data: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = -890.3 kJ 2 H2(g) + O2(g) → 2 H2O(l) H° = -571.6 kJ 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l) ΔH° = -3120.8 kJ

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