Question

(delta)S is positive for the reaction __________.

		a. Pb(NO3)2 (aq) + 2KI(aq) -> PbI2 (s) + 2KNO3 (aq)
		b. 2H2O (g) -> 2H2 (g) + O2 (g)
		c. H2O (g) -> H2O (s)
		d. NO (g) + O2 (g) -> NO2 (g)
		e. Ag+ (aq) + Cl- (aq) -> AgCl (s)

Answer 1

Delta S is positive if the number of moles of products will be more.

Also the order of disorderness is :

gases> liquids > solids

We know that the degree of disorderness is a measure of entropy.

So the order of entropy is : gases>liquids>solids

(a) products has less number of moles so deltaS is negative

(b) products have more number of moles so deltaS is positive

(c) gas converts to solid disorderness decreases so deltaS negative

(d) products have less number of moles so deltaS is negative

(e) here also the products having less disorderness so deltaS is negative

Therefore the correct option is (b)