Solid White Phosphorous undergoes polymerization to give red Phosphorous. What would be the bond enthalpy of P – P bond in red Phosphorous joining the two units of white phosphorous? Given that enthalpy of sublimation of white phosphorous is 59 KJ/mol and enthalpy of atomization is 316.25 KJ/mol of P(g)

P4(solid)$\to$   P4(gas)   $\Delta H^0=59KJ$
 P4(solid)  $\to$ 4P(gas)  $\Delta H^0=316.25\times 4=+1265KJ$
 P4(solid)  $\to$ 4P(gas)  $\Delta H^0=1265-59=1206KJ$
In P4 tetrahedral of white phosphorous, there are six identical P–P  bonds, therefore average     P–P  bond energy is   $\frac{1206}{6}=201KJ$.
In polymerization, on average one P–P  bond joining the two tetrahedral unit is formed,
 201-x = - 104 
                   x = 305 KJ/mole.