Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(b)

검증된 단계별 안내

Step 1: Identify the reaction. The given reaction involves the hydrogenation of benzene (C₆H₆) with 2 moles of hydrogen gas (H₂) in the presence of a catalyst to form cyclohexene (C₆H₁₀).

Step 2: Refer to Figure 16-2 for the enthalpy values. Look for the standard enthalpy of formation (∆H°f) values for benzene (C₆H₆), hydrogen gas (H₂), and cyclohexene (C₆H₁₀). These values are typically provided in a table or graph in the figure.

Step 3: Write the equation for calculating ∆H° for the reaction. Use the formula: ∆H° = Σ∆H°f(products) - Σ∆H°f(reactants).

Step 4: Substitute the values into the equation. For the products, use the ∆H°f value of cyclohexene. For the reactants, sum the ∆H°f values of benzene and 2 moles of hydrogen gas (note that the ∆H°f of H₂ gas is usually 0).

Step 5: Perform the subtraction to determine the ∆H° for the reaction. Ensure that the units are consistent (typically kJ/mol) and interpret the sign of ∆H° (negative for exothermic reactions, positive for endothermic reactions).

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주요 개념

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

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ∆H° < 0) or endothermic (absorbs heat, ∆H° > 0). Calculating ∆H° for a reaction involves using standard enthalpy values of formation for the reactants and products, allowing chemists to predict the energy changes associated with chemical reactions.

Catalysis

Catalysis refers to the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst. Catalysts work by providing an alternative reaction pathway with a lower activation energy, thus facilitating the conversion of reactants to products without being consumed in the process. In the given reaction, a catalyst is necessary to hydrogenate benzene into cyclohexane efficiently.

Hydrogenation of Aromatic Compounds

Hydrogenation of aromatic compounds involves the addition of hydrogen (H2) to the aromatic ring, converting it into a saturated compound. This reaction typically requires a catalyst, such as palladium or platinum, to proceed under mild conditions. In this case, benzene is being hydrogenated to form cyclohexane, which is a key transformation in organic synthesis and industrial applications.

Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:(b)