Q ΔMethane undergoes several different exothermic reactions...

Q $\Delta$ Methane undergoes several different exothermic reactions with gaseous chlorine. One of these forms chloroform, $\mathrm{CHCl}_{3}(\mathrm{~g})$. $$ \begin{aligned} \mathrm{CH}_{4}(\mathrm{~g})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CHCl}_{3}(\mathrm{~g})+3 \mathrm{HCl}(\mathrm{g}) \\ \Delta H_{\mathrm{rxn}}^{0}=-305.2 \mathrm{~kJ} / \mathrm{mol} \mathrm{rxn} \end{aligned} $$ Average bond energies per mole of bonds are: $\mathrm{C}-\mathrm{H}=$ $413 \mathrm{~kJ} ; \mathrm{Cl}-\mathrm{Cl}=242 \mathrm{~kJ} ; \mathrm{H}-\mathrm{Cl}=432 \mathrm{~kJ} .$ Use these to calculate the average $\mathrm{C}-\mathrm{Cl}$ bond energy in chloroform. Compare this with the value in Table $15-2$.

Q $\Delta$ Methane undergoes several different exothermic reactions with gaseous chlorine. One of these forms chloroform, $\mathrm{CHCl}_{3}(\mathrm{~g})$.
$$
\begin{aligned}
\mathrm{CH}_{4}(\mathrm{~g})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CHCl}_{3}(\mathrm{~g})+3 \mathrm{HCl}(\mathrm{g}) \\
\Delta H_{\mathrm{rxn}}^{0}=-305.2 \mathrm{~kJ} / \mathrm{mol} \mathrm{rxn}
\end{aligned}
$$
Average bond energies per mole of bonds are: $\mathrm{C}-\mathrm{H}=$ $413 \mathrm{~kJ} ; \mathrm{Cl}-\mathrm{Cl}=242 \mathrm{~kJ} ; \mathrm{H}-\mathrm{Cl}=432 \mathrm{~kJ} .$ Use these to
calculate the average $\mathrm{C}-\mathrm{Cl}$ bond energy in chloroform. Compare this with the value in Table $15-2$.

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Key Concepts

Bond Energy

Bond energy, also known as bond dissociation energy, is the average amount of energy needed to break one mole of a particular type of bond in the gas phase. This concept is used to estimate the energy changes in chemical reactions based on the bonds that are broken and the bonds that are formed.

Enthalpy of Reaction

The enthalpy of reaction is the overall heat change that occurs during a chemical reaction. It can be calculated using the bond energy approach by subtracting the total energy of bonds formed from the total energy of bonds broken, with a negative value indicating an exothermic process.

Bond Energy Approach

The bond energy approach involves using tabulated average bond energies to estimate the enthalpy change for reactions. This method calculates reaction enthalpy by accounting for the energy required to break bonds in reactants and the energy released upon bond formation in products.

Reaction Energetics

Reaction energetics is a fundamental concept in chemistry that studies the energy changes during chemical reactions. It focuses on understanding how energy is absorbed or released as bonds are broken and formed, which is key to predicting reaction spontaneity and stability.

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