From the enthalpies of reaction H₂(g) + F₂(g) → 2 HF(g) ΔH = -537 kJ C(s) + 2 F₂(g) → CF₄(g) ΔH = -680 kJ 2 C(s) + 2 H₂(g) → C₂H₄(g) ΔH = +52.3 kJ Calculate H for the reaction of ethylene with F₂: C₂H₄(g) + 6 F₂(g) → 2 CF₄(g) + 4 HF(g)

검증된 단계별 안내

Identify the target reaction: \( \text{C}_2\text{H}_4(g) + 6 \text{F}_2(g) \rightarrow 2 \text{CF}_4(g) + 4 \text{HF}(g) \).

Use Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step of the reaction.

Write the given reactions and their enthalpy changes: \( \text{H}_2(g) + \text{F}_2(g) \rightarrow 2 \text{HF}(g) \), \( \Delta H = -537 \text{ kJ} \); \( \text{C}(s) + 2 \text{F}_2(g) \rightarrow \text{CF}_4(g) \), \( \Delta H = -680 \text{ kJ} \); \( 2 \text{C}(s) + 2 \text{H}_2(g) \rightarrow \text{C}_2\text{H}_4(g) \), \( \Delta H = +52.3 \text{ kJ} \).

Manipulate the given reactions to match the target reaction: Reverse the third reaction to form \( \text{C}_2\text{H}_4(g) \) as a reactant, which changes its \( \Delta H \) to \( -52.3 \text{ kJ} \).

Add the enthalpy changes of the manipulated reactions to find the total \( \Delta H \) 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 enthalpy changes for complex reactions.

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. It is particularly useful in multi-step reactions, like the one presented in the question.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It provides the ratios in which substances react and form products, which is essential for determining the enthalpy changes in reactions. In the context of the question, stoichiometry helps in relating the amounts of C2H4 and F2 to the products CF4 and HF, allowing for accurate enthalpy calculations.

From the enthalpies of reaction H2(g) + F2(g) → 2 HF(g) ΔH = -537 kJ C(s) + 2 F2(g) → CF4(g) ΔH = -680 kJ 2 C(s) + 2 H2(g) → C2H4(g) ΔH = +52.3 kJ Calculate H for the reaction of ethylene with F2: C2H4(g) + 6 F2(g) → 2 CF4(g) + 4 HF(g)