Question

Is increase in entropy a Criterion for spontaneity ? explain ?

Answer 1

Explanation: Although spontaneous reactions are often exothermic, this is not a criterion for spontaneity. The best indicator of spontaneity in a reaction is the change in Entropy (S or DS). The Second Law of Thermodynamics states that for a reaction to be spontaneous, there must be an increase in entropy.

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Answer 2

i) Mixing of the two gases

ii) Spreading of a drop of ink in water beaker

These are isolated systems this process are accompanied by increase of randomness and hence increase of Entropy

Hence, it may be concluded that for spontaneous processes in the isolated systems the entropy change is positive

$\mathsf{\therefore}$ For all spontaneous process the total entropy change must be positive

$\\ \boxed{ \mathsf \red{ \Delta \: S_{Total} \: \: = \: \Delta \: S_{system} + \Delta \: S_{surr} \: > 0}}$

Criterion for the spontaneity in terms of entropy changes is as follows

a) if $\mathsf{ \Delta \: S_{Total}}$ is positive the process is spontaneous

b) if $\mathsf{ \Delta \: S_{Total}}$ is negative the direct process is non spontaneous

c) if $\mathsf{ \Delta \: S_{Total}}$ is zero the process is in equilibrium