At constant temperature and pressure, determine the entropy change, $\Delta S$ (> 0, < 0 or = 0) for the following processes and give the reasons:
(1) HCl(g) is dissolved in water to produce HCl(aq) solution;
(2) The decomposition of $NH_4Cl(s) \rightarrow NH_3(g) + HCl(g)$;
(3) 1 dm³ ($N_2$, g) + 1 dm³ (Ar, g) → 2 dm³ ($N_2$ + Ar, g);
(4) 1 dm³ ($N_2$, g) + 1 dm³ (Ar, g) → 1 dm³ ($N_2$ + Ar, g).