Question

Which of the reactions below will likely have the largest increase in entropy (ΔSrxn)?

1.) N2H4 (g) + H2 (g) -> 2 NH3 (g)

2.) C5H12 (l) + 8 O2 (g) -> 6 H2O (g) + 5 CO2 (g)

3.) Na+ (g) + Cl- (g) -> NaCl (s)

4.) S3 (g) + 9 F2 (g) -> 3 SF6 (g)

Answer 1

we know that gases have more randomness (more entropy ) than liquids and solids.

Thus the reactions which yield more number of gaseous products than the reactants lead to greater increase in entropy.

Hence

reaction 2

C5H12(l) + 8O2(g) --------------> 6H2O(g) + 5Co2(g)

yields 11 moles of gases as products against 8 moles of gas reactants.

In all the other reactions the gaseous products are less than the moles of reactant gases.

Thus OPTION 2 is the one with highest entropy increase.