Consider the following data
Heat of combustion of H 2 (g) =-241.8 kJ mol -1 Heat of combustion of C (s) =-393.5 kJ mol
-1
Heat of combustion of C 2 H 5 OH(a)=-1234.7 kJ mol -1
The heat of formation of C 2 H 5 OH(a) is (-)_____kJ mol -1 (Nearest integer).
Text Solution
Verified by Experts278
(278) C 2 H 5 OH(l) 
2 CO 2 (g)+3H 2 O(l)+ + 3O 2 (g)
Heat of combustion = Heat of formation of products - Heat of formation of reactants
Heat of combustion of hydrogen is equal to heat formation of water, and heat of combustion of carbon is equal to heat of formation of carbon dioxide.
H C =[2 
H f °(CO 2 )+3 
H f 0 (H 2 O)]-[ 
H f 0 (C 2 H 5 OH(a))]
-1234.7 = [2 x (-393.5) + 3 x (-241.8)] -[ 
H f °(C 2 H 5 OH(a))]
H f °C 2 H 5 OH = -277.7 kJ / mol
-278 kJ/mol
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