How do you use Hess's Law to calculate the enthalpy change for the reaction?

#WO_3(s) + 3H_2(g) -> W(s) + 3H_2O(g)#
from the following equations:
#2W(s) + 3O_2(g) -> 2WO_3(s)#
#Delta H = -1685.4 kJ#
#2H_2(g) + O_2(g) -> 2H_2O(g)3#
#Delta H = -477.84 kJ#

1 Answer
P dilip_k
Apr 16, 2016

#2WO_3(s)->2W(s)+3O_2(g),DeltaH =+1685.4kJ#
Dividing the eq by 2 we have
#WO_3(s)->W(s)+3/2O_2(g),DeltaH =+842.7kJ....(.1)#
Again
#2H_2(g)+O_2(g)->2H_2O(g),DeltaH=-477.8kJ#
Multiplying this eq by #3/2#
#3H_2(g)+3/2O_2(g)->3H_2O(g),DeltaH=-716.7kJ.....(2)#

Adding Eq(1) with eq (2)

#WO_3(s)+3H_2(g)->W(s)+H_2O(g), Delta H =842.7-716.7=126kJ#

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