Question

White phosphorus exists as $P_{4}$ molecules with phosphorus atoms at the corners of a tetrahedron. (IMAGE NOT COPY) (a) Elemental phosphorus reacts with $\mathrm{Cl}_{2}$ to form $\mathrm{PCl}_{3}$ Write a balanced chemical equation for this reaction. (b) The standard enthalpy of formation $\left(\Delta_{f} H\right)$ of $\mathrm{P}_{4}(\mathrm{g})$ is $+58.9 \mathrm{kJ} / \mathrm{mol} ;$ for $\mathrm{PCl}_{3}(\mathrm{g})$ it is $-287.0 \mathrm{kJ} / \mathrm{mol}$ Use these numbers to calculate the enthalpy of the reaction of $\mathrm{P}_{4}(\mathrm{g})$ and $\mathrm{Cl}_{2}(\mathrm{g})$ to give $\mathrm{PCl}_{3}(\mathrm{g})$ (c) Based on the equation in (a), determine what bonds are broken and what bonds are formed. Then, use this information along with the value of $\Delta_{\mathrm{r}} H$ calculated in (b) and the bond dissociation enthalpies for the $P-P$ and $C l-C l$ bonds from Table 8.9 to estimate the bond dissociation enthalpy for the $\mathrm{P}-\mathrm{Cl}$ bonds. How does your estimate compare with the value in Table $8.9 ?$

          White phosphorus exists as $P_{4}$ molecules with phosphorus atoms at the corners of a tetrahedron.
(IMAGE NOT COPY)
(a) Elemental phosphorus reacts with $\mathrm{Cl}_{2}$ to form $\mathrm{PCl}_{3}$ Write a balanced chemical equation for this reaction.
(b) The standard enthalpy of formation $\left(\Delta_{f} H\right)$ of $\mathrm{P}_{4}(\mathrm{g})$ is $+58.9 \mathrm{kJ} / \mathrm{mol} ;$ for $\mathrm{PCl}_{3}(\mathrm{g})$ it is $-287.0 \mathrm{kJ} / \mathrm{mol}$ Use these numbers to calculate the enthalpy of the reaction of $\mathrm{P}_{4}(\mathrm{g})$ and $\mathrm{Cl}_{2}(\mathrm{g})$ to give  $\mathrm{PCl}_{3}(\mathrm{g})$
(c) Based on the equation in (a), determine what bonds are broken and what bonds are formed. Then, use this information along with the value of $\Delta_{\mathrm{r}} H$ calculated in (b) and the bond dissociation enthalpies for the $P-P$ and $C l-C l$ bonds from Table 8.9 to estimate the bond dissociation enthalpy for the $\mathrm{P}-\mathrm{Cl}$ bonds. How does your estimate compare with the value in Table $8.9 ?$

Added by Robert F.

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