If a process leads to the arrangement in a system, it will have a negative entropy, whereas if disorder increases, the entropy will be positive. When the number of moles of a gas increases, or ice melts, the disorder increases. Freezing of water, crystallization, combination reactions etc, leads to an arrangement.

${\mathrm{CO}}_2 \left(\mathrm{s}\right)\to {\mathrm{CO}}_2 \left(\mathrm{g}\right); ∆\mathrm{S}=+\mathrm{ve} \left(∆{\mathrm{n}}_{\mathrm{g}}>0\right)$

${\mathrm{N}}_2 \left(\mathrm{g}\right)+3{\mathrm{H}}_2 \left(\mathrm{g}\right)\to 2{\mathrm{NH}}_3\left(\mathrm{g}\right); ∆\mathrm{S}=-\mathrm{ve} \left(∆{\mathrm{n}}_{\mathrm{g}}=-\mathrm{ve}\right)$

${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\to \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right); ∆\mathrm{S}=+\mathrm{ve} \left(∆{\mathrm{n}}_{\mathrm{g}}>0\right)$

Dissolution of ${\text{I}}_2$ in ${\mathrm{H}}_2\mathrm{O}; \mathrm{\Delta S}=+\mathrm{ve}$.