Question

${\Delta }_{r}H$ of which reaction correctly represents the lattice enthalpy of $NaCl(s)?$

• A. $NaCl(s)\to Na(g)+Cl(g)$
• B. $NaCl(s)\to N{a}^{+}(g)+C{l}^{-}(g)$
• C. $Na(g)+Cl(g)\to NaCl(s)$
• D. $N{a}^{+}(g)+C{l}^{-}(g)\to NaCl(s)$

Answer 1

Answer: (B)

Lattice enthalpy of an ionic solid like $NaCl(s)$ is the energy required to completely separate one mole of solid ionic compound into gaseous constituent ions. For $NaCl(s)$
$\underset{1\text{mole}}{NaCl(s)}\stackrel{\text{Lattice enthalpy}}{\to }N{a}^{+}(g)+C{l}^{+}(g)$
So here, ${\Delta }_{u}H={\Delta }_{r}H=$ enthalpy of reaction.