Answer
See the answer below.
Work Step by Step
a) $P_4(g)+6\ Cl_2(g)\rightarrow 4\ PCl_3(g)$
b) From the data given:
$4×-287.0-1×+58.9=-1206.9\ kJ/mol$
c) Bonds broken: 6 P-P, 6 Cl-Cl
Bonds formed: 12 P-Cl
Enthalpy of reaction:
$-1206.9\ kJ/mol=6×201+6×242-12×x$
$x=322\ kJ/mol$
Table 8.8 says it's 326 kJ/mol, so it's a reasonable estimate.
