(b) Determine ΔH for the atomization of naphthalene using Hess’s law and the data in Appendix C. (ΔHf° of solid naphthalene is 77.1 kJ/mol and the molar heat of sublimation of naphthalene is 72.9 kJ/mol.)

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

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Identify the process of atomization for naphthalene, which involves converting solid naphthalene into gaseous atoms.

Use Hess's Law, which states that the total enthalpy change for a reaction is the same, no matter how many steps the reaction is carried out in.

Recognize that the enthalpy change for atomization can be found by adding the enthalpy of sublimation to the enthalpy of formation of gaseous naphthalene.

Calculate the enthalpy of formation of gaseous naphthalene by adding the enthalpy of formation of solid naphthalene to the molar heat of sublimation.

The enthalpy change for atomization is the sum of the enthalpy of formation of gaseous naphthalene and the energy required to break all bonds in the gaseous naphthalene to form individual atoms.

주요 개념

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Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for each step of the reaction, regardless of the pathway taken. This principle allows us to calculate the enthalpy change for a reaction by using known enthalpy changes of related reactions, making it essential for determining ΔH in complex processes like atomization.

Standard Enthalpy of Formation (ΔHf°)

The standard enthalpy of formation (ΔHf°) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. For naphthalene, the given ΔHf° of 77.1 kJ/mol indicates the energy required to form solid naphthalene from its constituent elements, which is crucial for calculating the overall enthalpy change during atomization.

Molar Heat of Sublimation

The molar heat of sublimation is the amount of energy required to convert one mole of a solid directly into a gas at constant pressure. For naphthalene, the molar heat of sublimation of 72.9 kJ/mol represents the energy needed to transition from solid to gas, which is a key component in determining the total enthalpy change for the atomization process.