Answer
$-610\text{ kJ}$
Work Step by Step
$P_4O_{10(s)}\Rightarrow P_{4(s)}+5O_{2(g)}$ 2967.3 kJ
$6PCl_{s(g)}\Rightarrow 6PCl_{3(g)}+6Cl_{2(g)}$ 505.2kJ
$P_{4(s)}+6Cl_{2(g)}\Rightarrow 4PCl_{3(s)}$ -1225.6 kJ
$10PCl_{3(g)}+5O_{2(g)}\Rightarrow 10Cl_3PO_{(g)}$ -2857 kJ
Summing all of these enthalpy values, we reach the final value of $-610\text{ kJ}$.
