Question

(i) Use the expressions
${CX}_4$(g) $⟶$ C(s) + ${2X}_2$(g)
$\Delta H={-\Delta H}_f$
$C\left(s\right)⟶C\left(g\right)$ ; $\Delta H$=718 kJ/mol
and
${2X}_2$(g) $⟶$ 4X(g) ; $\Delta$H = 2D(X X)
where $X=F,Cl$ to the enthalpy change for the two processes
${CX}_4\left(g\right)⟶C\left(g\right)+4X\left(g\right)$
What is the average $CX$ bond energies for the species ${CX}_4$(g) ?

(where $X=F,Cl$)

• A. 329.5 kJ/mol, 426.75 kJ/mol
• B. 426.75 kJ/mol, 329.5 kJ/mol
• C. 329.5 kJ/mol, 526.75 kJ/mol
• D. All of the above

Answer 1

Answer: (B)

426.75 kJ/mol, 329.5 kJ/mol

Add eq. (i), (ii) and (iii)
$X_1$(g) $⟶$ C(g) + 4X
$\Delta H={-\Delta H}_1+718+2D\left(XX\right)X=F$
$\Delta$H = +679.6 + 718 + 2 $\times$154.7
$\Delta$H = 1707
Average bond energy of C F bond
=$\frac{1707}{4}$ =426.75
(C F 1055)
X = Cl
$\Delta$H = 106.6 + 718 + 2(246.7) = 1318
Average bond energy of C Cl bond = 329.5 Kg