Phosphorus and Chlorine Gases Combine to Produce Phosphorus Trichloride $P _ { 2 }$

Phosphorus and chlorine gases combine to produce phosphorus trichloride:
$P _ { 2 }$ (g) + $\mathrm { 3Cl } _ { 2 }$ (g) ? $2 \mathrm { PCl } _ { 3 }$ (g)
?_rG° at 298 K for this reaction is -642.9 kJ mol^-1.The value of ?_rG at 298 K for a reaction mixture that consists of $1.8 \text { atm } P _ { 2 }$ $1.2 \mathrm {~atm} \mathrm { Cl } 2$ and $0.66 \text { atm } \mathrm { PCl } _ { 3 }$ is ________ kJ mol^-1.

A) -5.51 × 10³
B) -90.0
C) -71.1
D) -4.87 × 10³
E) -647.8