The standard enthalpy of the reaction SiCl4(g) + 2 Mg(s)  2 MgCl2(s) + Si(s) at 25 C is 625.6 kJ mol1. Mg(s) and Si(s) are, respectively, the stable forms of the elements magnesium and silicon at 25 C and 1 bar. The standard enthalpy of formation of MgCl2(s) is 641.2 kJ mol1. What is the standard enthalpy of formation of SiCl4(g)? A. 656.8 kJ mol1 B. 15.6 kJ mol1 C. +15.6 kJ mol1 D. 1282.4 kJ mol1 E. 656.8 kJ mol1