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

4al + 3o2 → 2al2o3 what does the "3" in front of o2 stand for? a) it indicates that there are 5 oxygen atoms after you add the coefficient and the subscript. b) it indicates that that there are are total of 6 oxygen atoms all bonded together as a single molecule. c) it indicates that there are 3 oxygen molecules chemically bonded to each other in the reaction. d) it indicates that there are 3 separate oxygen molecules in the reaction.