Question

Dissolution of which compound in water is exothermic?

• A. $S{O}_2$
• B. $N{H}_{4}N{O}_3$
• C. $LiCl$
• D. Both $A$ and $C$

Answer 1

Answer: (D)

Both $A$ and $C$

Heat of hydration is given out when sulphur dioxide dissolves in water as it results in the formation of sulphuric acid. It is an exothermic process and heat is given out.
${2SO}_2+{2H}_{2}O+O_2\to 2H_2{SO}_4$

Heat of hydration is given out when lithium chloride dissolves in water as it results in the formation of $L{i}^{+}$${}_{\left(aq\right)}$ and $C{l}^{-}$${}_{\left(aq\right)}$. Its an exothermic process as heat of solution of $L{i}^{+}$${}_{\left(g\right)}$ and $C{l}^{-}$${}_{\left(g\right)}$is greater than lattice energy of $LiCl$${}_{\left(s\right)}$.

But Heat of hydration is positive when ammonium nitrate dissolves in water as it results in the formation of $N{H}_4^{+}$${}_{\left(aq\right)}$ and $N{O}_3^{-}$${}_{\left(aq\right)}$. Its an endothermic process as heat of solution of $N{H}_4^{+}$${}_{\left(g\right)}$ and $N{O}_3^{-}$${}_{\left(g\right)}$is less than lattice energy of $N{H}_{4}N{O}_3$${}_{\left(s\right)}$.