Find the amount (in moles) of C-C bonds that must be broken when 1.0 mole of C(g) is formed from

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Find the amount (in moles) of C-C bonds that must be broken...

Find the amount (in moles) of $\mathrm{C}-\mathrm{C}$ bonds that must be broken when $1.0$ mole of $\mathrm{C}(g)$ is formed from $\mathrm{C}$ (diamond). Calculate the $\Delta H$ of sublimation of diamond from the data in Appendix II, Table $\mathrm{B}$. Then do the calculation using the $\mathrm{C}-\mathrm{C}$ bond energy in Table 9.3. Suggest a reason for the difference between the two values.

Key Concepts

Bond Energy

Bond energy is the amount of energy required to break one mole of a specific chemical bond in a substance in the gas phase. In problems involving the breaking or formation of bonds, bond energy provides an estimate of the energy change associated with these processes. It is a fundamental concept for understanding reaction energetics and can be used to approximate the enthalpy changes in chemical reactions, though it often neglects the effects of the surrounding environment and solid-state interactions.

Enthalpy of Sublimation

The enthalpy of sublimation is the heat required to convert a substance from its solid phase directly into its gaseous phase at a constant pressure. This concept is essential for understanding phase transitions and is experimentally determined for different allotropes of an element. In thermochemical calculations, it represents the energy needed to overcome the lattice energies holding a solid together, providing a practical measure of the energy required to detach atoms from a structured lattice.

Crystal Structure and Bonding in Solids

Crystal structure and bonding in solids refer to how atoms are arranged and connected by chemical bonds in a crystalline material. In the context of diamond, each carbon atom is tetrahedrally coordinated to four other carbon atoms by strong covalent bonds. Understanding the coordination number and the nature of these bonds is critical when calculating how many bonds must be broken to liberate atoms from the crystalline lattice, such as in sublimation processes.

Thermochemical Cycle Analysis

Thermochemical cycle analysis involves constructing a hypothetical cycle of steps whose total energy change sums to the observed enthalpy change of a reaction. This concept allows one to compare theoretical calculations using bond energies with experimental enthalpy values, like the sublimation of diamond. Discrepancies between these values can arise due to factors such as lattice energy, bond strain in the crystal, or approximations made in not accounting for all energetic contributions in the bonding environment.

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