Question

6. For the chemical reaction C2H5OH(ℓ) + 3O2 (g) → 2CO2 + 3H2O (ℓ), if change in internal energy at 298K is 1368 KJ/mole, the change in enthalpy will be
(A) greater than 1368
(B) less than 1368
(C) equal to zero
(D) negative

Answer 1

the chemical reaction C2H5OH(ℓ) + 3O2 (g) → 2CO2(g) + 3H2O (ℓ).

from above chemical equation,

$\Delta n_g RT=(2 - 3)RT=-RT$

[ where ∆ng is the difference of number of gaseous compound of products to gaseous compound of reactants ]

given, change in internal energy, ∆U = 1368 KJ/mol

so, change in enthalpy , ∆H = ∆U + ∆$n_g$RT

= 1368 - RT < 1368 KJ/mole .

hence, it is clear that the change in enthalpy will be less than 1368.

hence, option (B) is correct choice.