Question

Determine the standard heat of each of the following reactions at 25 C:

1. CH3OH (g) + 1/2 O2 (g) --> HCHO (g) + H2O (g)

2. C2H4 (g) + 1/2 O2 (g) --> {(CH2)2}O (g)

3. H2S (g) + 2 H2O (g) --> 3H2 (g) + SO2 (g)

Answer 1

For this we will make use of standard heat of formation data available in standard literature

Following is the heat of formation Data

Name	Hf (KJ/mol)
CH3OH	-238.6
O2	0
HCHO	-108
H2O	-241.8
C2H4	52.3
(CH2)2O	-52
H2S	-20.1
H2	0
SO2	-296.1

Now,

Standard Heat of reaction = (Sum of heat of formation of products) - (Sum of heat of formation of reactants)

We will use the above equation to solve the given problem

For Reaction 1

	CH3OH	+	(1/2)O2	--->	HCHO	+	H2O
Hf	-238.6		0		-108		-241.8

Hreactions = (-108 + (-241.8)) - ((-238.6) +0) = -111.2 KJ/mol

For Reaction 2

	C2H4	+	(1/2)O2	--->	(CH2)2O
Hf	52.3		0		-52

Hreaction = (-52) - (52.3 +0) = - 104.3 KJ/mol

For reaction 3

	H2S	+	2 H2O	--->	3 H2	+	SO2
Hf	-20.1		-241.8		0		-296.1

Hreaction = ( (3*0)+(-296.1)) - ( -20.1 + 2*(-241.8)) = 207.6 KJ/mole