Question

The heat of atomisation of $P{H}_3\left(g\right)$ is $228kcalmo{l}^{-1}$ and that $P_2{H}_4\left(g\right)$ is $355kcalmo{l}^{-1}$ . The energy of the $P--P$ bond is (in kcal):

• A. 102
• B. 51
• C. 26
• D. 204

Answer 1

The correct option is B 51

The balanced chemical equation for the atomization of phosphine is $P{H}_3⟶P+3H;\Delta H=228$
$e_{p--H}=\frac{228}{3}$
The balanced chemical equation for the atomization of $P_2{H}_4\left(g\right)$ is $H_{2}P--P{H}_2⟶2P+4H;\Delta H=355$
$e_{p--p}+4\times e_{p--H}=355$
$e_{p--p}+4\times \frac{228}{3}=355$
$e_{p--p}=51$
The energy of the $P--P$ bond is 51 kcal.