Calculate the entropy change (`DeltaS`) for the following reaction at `25^@C`.
`SO_2(g) + 1/2O_2(g) to SO_3(g)`
The absolute entropies at `25^@C` and 1 atm pressure for `SO_2(g), O_2(g) and SO_3(g)` are 248.5, 205.0 and 256.2 J K^(-1) mol^(-1)` respectively.

Explanation

We know that, `DeltaS^(@)= Sigma Delta S_(("products"))^(@) - Sigma DeltaS_(("reactants"))^(@)`
`= {Delta S^(@) [SO_(3)(g)]}- {Delta S[SO_(2)(g)] + (1)/(2) xx Delta S^(@) [O_(2)(g)]}`
`Delta S^(@)= {256.2}- {248.5 + (1)/(2) xx 205.0}`
`Delta S^(@)= 256.2- 351.0`
`= -94.8 JK^(-1) mol^(-1)`
`therefore` The standard entropy change `DeltaS^(@)` for the reactant is is `-94.8JK^(-1) mol^(-1)`