Question

Molar heat capacity of `CD_(2)O` (deuterated form of formaldehyde) at constant pressure in `9 cal mol^(-1) K^(-1) at 1000K`. Calculate the entropy change associated with cooling of `3.2 g` of `CD_(2)O` vapour from `1000 to 900K`.

Answer 1

`DeltaH` for cooling `CD_(2)O = mS DeltaT = (3.2)/(32) xx 9 xx 100 = 90 cal`
Therefore, cooling is exothermic, `DeltaH =- 90 cal`
Now, `DeltaS = (DeltaH)/(T) = - (90)/(900) =- 0.1 cal deg^(-1)`