Question

Given that $△H=0$ for mixing of two gases. Explain whether the diffusion of these gases into each other in a closed container is a spontaneous process or not?

Answer 1

The spontaneity of any process depends on the sign of change in Gibbs free energy (i.e. $△G)$

A negative $△G$ means the reaction will be spontaneous, it includes the contribution of the other factors like enthalpy(H) and entropy(S).

For diffusion of gases in a closed container, entropy change(i.e. $△S$) is positive, as randomness increases due to mixing of gases.

Using Gibb's free energy equation,

$△G=△H-T△S$

Given, $△H=0$

$△G=-T△S=$negative

$△G$ will be negative (as positive value of $△S$ will give a negative $T△S$)

It is a spontaneous process. Although enthalpy change is zero but randomness or disorder(i.e. $△S$) increases.