Question

Enthalpy of combustion of graphite H2 and ethanol is – 94 Kcal , -68.4 Kcal and – 327 Kcal Calculate the enthalpy of formation of ethanol

Answer 1

Answer:

2C(s)+3H

2

(g)+

2

1

O

2

(s)⟶C

2

H

5

OH(l)

Given: C(s)+O

2

(g)⟶

ΔH

1

=−94Kcal

CO

2

(g)

.....(i)

H

2

(s)+

2

1

O

2

(g)⟶

ΔH

2

=−68Kcal

H

2

O(l)

......(ii)

C

2

H

5

OH(l)+3O

2

(g)⟶

ΔH

3

=−372Kcal

2CO

2

(g)

+3H

2

O(l)......(iii)

Operate: 2(i)+3(ii)−(iii) to get Δ

f

H=2(ΔH

1

)+3(ΔH

2

)−ΔH

3

=2(−94)+3(−68)−(−327) =65Kcalmol

−1

Hence, the heat of formation of ethyl alcohol is 65 Kcal/mol.