Question

Based on your chemical intuition, do you expect the reaction of: H2 + SiH2 ? SiH4

to be exothermic or endothermic? Use chemical principles to support your argument.

Answer 1

if forming CH4 is exothermic dHf = -74.8 kJ/mol
them forming SiH4 should be

CH4 is more common than CH2
so SiH4 should be more common than SiH2
more common is more stable
more stable is less energetic
less energetic is exothermic dHf's
======================================...

form the literature:

SiH4(g) dHf = + 34 kJ/mol


SiH2 dHf = + 273kj/mol


should be exothermic:

H2 + SiH2 -> SiH4
dHrxn = (dHf prod) - (dHf reactants)
dHrxn = (34) - (273)
dHrxn = - 239 kJ/mol

that exo