Question

The heat of atomisation of $P{H}_3(g)$ and $P_2{H}_4(g)$ are $954kJmo{l}^{-1}$ and $1485kJmo{l}^{-1}$ respectively .The P-P bond energy in $kJmo{l}^{-1}$ is

• A. 213
• B. 426
• C. 318
• D. 1272.

Answer 1

Answer: (A)

In $P{H}_{3(g)}$, energy required to break $3P-H$ bonds

$=954kJmo{l}^{-1}$

$\therefore$ Energy required to break $1P-H$ bond

$=\frac{954}{3}=318kJmo{l}^{-1}$

In $P_2{H}_{4(g)}$, energy of $1P-P$ bond

$+4P-H$ bonds $=1485kJmo{l}^{-1}$

$\because$ Energy of $1P-H$ bond $=318kJmo{l}^{-1}$

$\therefore$ Energy of $4P-H$ bonds

$=318\times 4=1272kJmo{l}^{-1}$

Thus, the $P-P$ bond energy $=1485-1272=213kJmo{l}^{-1}$