$\mathrm{NaCl}(\mathrm{s}) \longrightarrow \mathrm{Na}(\mathrm{g})+\mathrm{Cl}(\mathrm{g})$

$\mathrm{NaCl}(\mathrm{s}) \longrightarrow \mathrm{Na}^{+}(\mathrm{g})+\mathrm{Cl}^{-}(\mathrm{g})$

$\mathrm{Na}(g)+\mathrm{Cl}(g) \longrightarrow \mathrm{NaCl}(s)$

$\mathrm{Na}^{+}(g)+\mathrm{Cl}^{-}(g) \longrightarrow \mathrm{NaCl}(\mathrm{s})$

$\mathrm{H}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{H}(\mathrm{g})$

Liquid water crystallises to ice

Temperature of ice is raised from 10 K to 115 K

$2 \mathrm{NaHCO}_3$ (s) $\longrightarrow \mathrm{Na}_2 \mathrm{CO}_3$ (s) $+\mathrm{CO}_2$ (g) $+\mathrm{H}_2 \mathrm{O}$ (s)

The energy of the isolated system plus the energy of the surrounding is constant.

The energy of the isolated system minus the energy of the surrounding is constant.

The energy of an isolated system is constant.

The energy of an isolated system varies.

$e^8$

$e^9$

$e^{10}$

$e^{11}$