Question

In which of the following cases is the sign of the entropy change (ΔS) positive?

options:

2 KCl(g) + 3 O2(g) --> 2 KClO3(s)

2 HgO(s) --> 2 Hg(l) + O2(g)

4 NH3(g) + 7 O2(g) --> 4 NO2(g) + 6 H2O(g)

2 H2S(g) + SO2(g) --> 3 S(s) + 2 H2O(g)

2 Na(s) + Cl2(g) --> 2 NaCl(s)

Answer 1

Entropy is a measure of randomness. Entropy os sollid< liquid <gas.

Entropy changeS is positive if No of moles of product is grater than No. of moles of reactants.

or when  n = n_p - n_r is >1

When we consider the heterogeneous equilibrium we consider only the number of moles of gaseous reactants, because randomness is maximum for gaseous reactans and this cannot be compared with randomness of pure liquid or solid

A) 2KCl  _g + 3O_{2 g} 2KClO_{3 s}

_ng  = 0 - (2+3) = -5 ;S is negative

B) 2HgO _s    2Hg _l  + O_{2  g   ng} = 1+0 -0 = 1

S is positive

C)  ng = (4+6) - (4+7) = 10 -11 = -1

S is negative

D)ng = 2 - (2+1) =2 - 3 = -1

S is negative

E) S = 0 - (0+1) = -1

S is negative

S is positive only for option 2