Two compounds are isomers if they have the same chemical formula but different arrangements of atoms. Use Table 8.3 to estimate H for each of the following gas-phase isomerization reactions and indicate which isomer has the lower enthalpy. (d) Methyl isocyanide → Acetonitrile

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Identify the chemical formulas for methyl isocyanide and acetonitrile. Both compounds have the formula C2H3N.

Use Table 8.3 to find the standard enthalpy of formation (\( \Delta H_f^\circ \)) for each compound: methyl isocyanide and acetonitrile.

Calculate the enthalpy change (\( \Delta H \)) for the isomerization reaction using the formula: \( \Delta H = \Delta H_f^\circ (\text{products}) - \Delta H_f^\circ (\text{reactants}) \).

Substitute the \( \Delta H_f^\circ \) values from Table 8.3 into the equation to find \( \Delta H \) for the reaction: Methyl isocyanide → Acetonitrile.

Determine which isomer has the lower enthalpy by comparing the \( \Delta H_f^\circ \) values of methyl isocyanide and acetonitrile. The isomer with the lower \( \Delta H_f^\circ \) value is more stable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Isomerism

Isomerism refers to the phenomenon where two or more compounds share the same molecular formula but differ in the arrangement of atoms. This can lead to distinct physical and chemical properties, making isomers an important concept in organic chemistry. Isomers can be classified into structural isomers, which differ in connectivity, and stereoisomers, which differ in spatial arrangement.

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). In the context of isomerization reactions, comparing the enthalpy changes helps determine which isomer is more stable, as lower enthalpy corresponds to greater stability.

Gas-Phase Reactions

Gas-phase reactions occur when reactants and products are in the gaseous state, allowing for different kinetic and thermodynamic behaviors compared to reactions in solution or solid states. In gas-phase isomerization, factors such as molecular interactions and energy barriers play a crucial role in determining the reaction pathway and the stability of the resulting isomers.

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