Sand Is Converted to Pure Silicon in a Three Step

Multiple Choice

Sand is converted to pure silicon in a three step process. The third step is
SiCl₄(g) + 2Mg(s)  2MgCl₂(s) + Si(s) H = -625.6 kJ
What is the enthalpy change when 25.0 mol of silicon tetrachloride is converted to elemental silicon?

A) -25.0 kJ
B) -7820 kJ
C) -1.56 × 10⁴ kJ
D) -3.13 × 10⁴ kJ
E) none of the above