Which of the following would you predict to have a positive value for º ?

agcl(s) → ag+(aq) + cl-(aq)

h2o(g) → h2o(l)

2 na(s) + cl2(g) → 2nacl(s)

br2(l) → br2(s)

Given:

AgCl (s) ===> Ag+ (aq) + Cl- (aq)
- negative entropy

H2O(g) ===> H2O(l)
- positive entropy

2Na (s) + Cl2 (g) ===> 2NaCl (s)
- positive entropy

Br2(l) ===> Br2 (s)
-positive entropy

They are identified to have positive or negative values of entropy based on the phases of the reactants and products. 

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged