Question

The ∆H and ∆S of the reaction H2 + Cl2 gives HCL are respectively -92KJ and -95J calculate the value of ∆G and predict the reaction spontaeous or non spontaneous

Answer 1

Answer : The value of standard Gibbs free energy is -91.81 kJ and the reaction is spontaneous.

Explanation :

Gibbs free energy : It is defined as the amount of energy that is available to do useful work.

A reaction to be spontaneous when $\Delta G<0$

A reaction to be non-spontaneous when $\Delta G>0$

For the reaction to be spontaneous, the Gibbs free energy of the reaction $\Delta G$ is negative or we can say that the value of $\Delta G$ is less than zero.

Formula used :

$\Delta G^o=\Delta H^o-T\Delta S^o$

where,

$\Delta G^o$ = standard Gibbs free energy  = ?

$\Delta H^o$ = standard enthalpy = -92 kJ = -92000 J

$\Delta S^o$ = standard entropy = -95 J/K

T = temperature of reaction = 298 K  (room temperature)

Now put all the given values in the above formula, we get:

$\Delta G^o=(-92000J)-(298K\times -95J/K)$

$\Delta G^o=-91810J=-91.81kJ$

Thus, the value of standard Gibbs free energy is -91.81 kJ and the reaction is spontaneous.