Consider the following hypothetical reactions: A → B ΔH_I = +60 kJ B → C ΔH_II = -90 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.

검증된 단계별 안내

Identify the enthalpy changes for each reaction: \( \Delta H_{I} = +60 \text{kJ} \) for \( A \rightarrow B \) and \( \Delta H_{II} = -90 \text{kJ} \) for \( B \rightarrow C \).

Draw an enthalpy diagram with the y-axis representing enthalpy (H) and the x-axis representing the reaction progress.

Place substance A at the starting point on the y-axis. Since \( \Delta H_{I} = +60 \text{kJ} \), draw an upward arrow to represent the conversion of A to B, indicating an increase in enthalpy.

From B, draw a downward arrow to represent the conversion of B to C, since \( \Delta H_{II} = -90 \text{kJ} \), indicating a decrease in enthalpy.

Apply Hess's Law by adding the enthalpy changes of the two steps to find the overall enthalpy change for the reaction \( A \rightarrow C \).

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주요 개념

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

Enthalpy (ΔH)

Enthalpy is a thermodynamic quantity that represents the total heat content of a system. It is often expressed in kilojoules (kJ) and can indicate whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). In the given reactions, the positive and negative values of ΔH indicate the heat changes associated with the transformations between substances A, B, and C.

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the number of steps taken to achieve the reaction. This principle allows us to calculate the enthalpy change for a reaction by summing the enthalpy changes of individual steps, making it useful for constructing enthalpy diagrams and understanding the overall energy changes in a series of reactions.

Enthalpy Diagram

An enthalpy diagram visually represents the enthalpy changes of reactants and products in a chemical reaction. It typically shows the relative energy levels of the substances involved, allowing for a clear understanding of how energy is absorbed or released during the reaction process. In this case, the diagram would illustrate the transitions from A to B and then from B to C, highlighting the respective enthalpy changes.

Consider the following hypothetical reactions: A → B ΔHI = +60 kJ B → C ΔHII = -90 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.