Ch.7 - Thermochemistry

Tro - Chemistry: A Molecular Approach 6th Edition

Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217당신이 사용하는 게 아니라요?교과서 변경

Tro 6th Edition

Ch.7 - Thermochemistry

문제 81c

7장, 문제 81c

For each generic reaction, determine the value of ΔH₂ in terms of ΔH₁.
c. A → B + 2 C ΔH₁
1/2 B + C → 1/2 A ΔH₂ = ?

검증된 단계별 안내

Identify the stoichiometry of the reactions given. The first reaction is A → B + 2C with a heat change ΔH₁. The second reaction is 1/2 B + C → 1/2 A with a heat change ΔH₂.

To find ΔH₂, we need to reverse and adjust the stoichiometry of the first reaction to match the second reaction. Reversing the first reaction gives B + 2C → A, and the heat change for this reversed reaction would be -ΔH₁.

Adjust the coefficients of the reversed reaction to match those of the second reaction. Divide all coefficients in the reversed reaction by 2 to get 1/2 B + C → 1/2 A.

Since the coefficients of all substances in the reversed reaction are halved, the heat change for this new reaction will also be half of -ΔH₁, which is -1/2 ΔH₁.

Thus, ΔH₂ for the reaction 1/2 B + C → 1/2 A is -1/2 ΔH₁.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

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

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows us to calculate the enthalpy change for a reaction by combining known enthalpy changes of related reactions.

Enthalpy Change (ΔH)

Enthalpy change (ΔH) is a measure of the heat content of a system 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 associated with chemical reactions.

Stoichiometry in Reactions

Stoichiometry involves the quantitative relationships between the reactants and products in a chemical reaction. It allows us to relate the amounts of substances consumed and produced, which is essential for calculating enthalpy changes when reactions are manipulated or combined.

관련 실천

교과서 질문

For each generic reaction, determine the value of ΔH₂ in terms of ΔH₁.

a. A + B → 2 C ΔH₁

2 C→ A + B ΔH₂ = ?

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교과서 질문

For each generic reaction, determine the value of ΔH₂ in terms of ΔH₁.

b. A + 1/2 B → C ΔH₁

2 A + B → 2 C ΔH₂ = ?

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교과서 질문

Calculate ΔH_rxn for the reaction:

Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g)

Use the following reactions and given ΔH's:

2 Fe(s) + 3/2 O₂(g) → Fe₂O₃(s) ΔH = –824.2 kJ

CO(g) + 1/2 O₂(g) → CO₂(g) ΔH = –282.7 kJ

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교과서 질문

Instant cold packs used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the endothermic reaction: NH₄NO₃(s) → NH₄⁺(aq) + NO₃^– (aq) In order to measure the enthalpy change for this reaction, 1.25 g of NH₄NO₃ is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 °C and the final temperature (after the solid dissolves) is 21.9 °C. Calculate the change in enthalpy for the reaction in kJ. (Use 1.0 g/mL as the density of the solution and 4.18 J/g•°C as the specific heat capacity.)

Consider the generic reaction:

A + 2 B → C + 3 D ΔH = 155 kJ

Determine the value of ΔH for each related reaction.

a. 3 A + 6 B → 3 C + 9 D

b. C + 3 D → A + 2 B

c. 1/2 C + 3/2 D → 1/2 A + B

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