calculate the enthalpy of formation of ethane at 298k, if the enthalpies of combustion at ch2 and c2 h6 are -94.14, -68.47 and -373 k cal respectively.
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The fuel efficiency can be predieted from the amount of heat evolved for every gram of fule consumed.
(i) The combustion of methane is as follows :
CH
4(g)
+20
2(g)
→CO
2(g)
+2H
2
O
(1)
DHc=890.3KJmol−1
Molar mass of CH
4
=16
Heat produced per gram =
16
890.3
=55.64KJg
−1
(ii) The combustion of ethane is as follows :
C
2
H
6(g)
+
2
7
O
2(g)
→2CO
2(g)
+3H
2
O
(1)
DH
c
=1559.7KJmol
−1
Molar mass of C
2
H
6
=30
Heat produced per gram =
30
1559.7
=51.99KJg
−1
Thus, methane has greater fuel efficiency then ethane.
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