Question

Use the bond energies provided to estimate ?H°rxn for the reaction below.

PCl3(g) + Cl2(g) ? PCl5(l)
?H°rxn = ?
Bond Bond Energy (kJ/mol)
Cl-Cl 243
P-Cl 331

Answer 1

The estimated enthalpy change for the reaction PCl3(g) + Cl2(g) → PCl5(l), using the provided bond energies, is 409 kJ.

Step-by-step explanation:

To estimate the enthalpy change (ΔH°rxn) for the given chemical reaction using bond energies, we must consider the energy required to break the reactant bonds and the energy released upon forming the product bonds.

Given reaction: PCl3(g) + Cl2(g) → PCl5(l)

1. Calculate the energy required to break bonds in reactants (Endothermic process):
   1 P-Cl bond × 331 kJ/mol = 331 kJ/mol (as PCl3 has 3 P-Cl bonds)
   1 Cl-Cl bond × 243 kJ/mol = 243 kJ/mol
   Total energy required = 331 × 3 + 243 = 1246 kJ
2. Calculate the energy released upon forming bonds in products (Exothermic process):
   Since PCl5 has 5 P-Cl bonds,
   5 P-Cl bonds × 331 kJ/mol = 1655 kJ
3. Subtract the energy required from the energy released to find the enthalpy change:
   ΔH°rxn = Energy of bonds formed - Energy of bonds broken
   ΔH°rxn = 1655 kJ - 1246 kJ = 409 kJ

Therefore, the estimated enthalpy change for the reaction is 409 kJ.

Answer 2

The estimated enthalpy change for the reaction PCl3(g) + Cl2(g) → PCl5(l) is 419 kJ, determined by calculating the energy to break the bonds of the reactants and subtracting it from the energy released by forming the products.

Step-by-step explanation:

The question involves estimating the enthalpy change (ΔH°rxn) for a chemical reaction using bond energies. To solve this, you need to consider the energies required to break the bonds in the reactants and the energies released when new bonds are formed in the products. For the given reaction PCl3(g) + Cl2(g) → PCl5(l), you would follow these steps:

1. Calculate the total energy required to break the bonds of the reactants: 1 mole of P-Cl bonds (3 × 331 kJ/mol for PCl3) and 1 mole of Cl-Cl bonds (243 kJ/mol).
2. Calculate the energy released by forming the products: 5 moles of P-Cl bonds in PCl5 (5 × 331 kJ/mol).
3. Subtract the energy required to break the bonds from the energy released to form the new bonds to get the net ΔH°rxn.

Using the values provided:

• Energy required to break bonds = (3 × 331) + 243 = 1236 kJ
• Energy released in forming bonds = 5 × 331 = 1655 kJ
• Enthalpy change (ΔH°rxn) = Energy released - Energy required = 1655 kJ - 1236 kJ = 419 kJ

Therefore, the estimated ΔH°rxn for the reaction is 419 kJ.