Sand is converted to pure silicon in a three step process. The third step isSiCl4 (g) + 2Mg (s) ? 2MgCl2 (s) + Si (s) ? H = - 625.6 kJWhat is the enthalpy change when 12.5 mol of silicon tetrachloride is converted to elemental silicon? A 12.5 kJB 3910 kJC 0.78 x 10^4 kJD 1.56 x 10^4 kJ

(C) 0.78*10⁴ kJ

Explanation:

The enthalpy of the reaction = - 625.6 kJ (Negative sign signifies heat released).

From the reaction,

1 mole of silicon tetrachloride undergoes reaction to produce 1 mole of elemental silicon with the release of energy 625.6 kJ

So,

For 12.5 moles of silicon tetrachloride:

The enthalpy is : - 625.6 * 12.5 kJ = 7820 kJ.

Rearranging in the form of answer as 7820 kJ = 0.78*10⁴ kJ (C)