Question

What is the heat of solution of sodium chloride from following data?
Hydration energy of $Na^+ = - 389.4\, kJ\, mol^{-1}$
Hydration energy of $Cl^- = - 382.3\, kJ\, mol^{-1}$
Lattice energy of $NaCl = - 776 \,kJ \,mol^{-1}$

• A. $+ 8.6\, kJ\, mol^{-1}$
• B. $+ 4.3\, kJ\, mol^{-1}$
• C. $- 4.3\, kJ\, mol^{-1}$
• D. $- 8.6\, kJ\, mol^{-1}$

Answer 1

Answer: (B)

Hydration energy of $NaCl = - 389.4 - 382.3$
$= -771.7\, kJ \,mol^{-1}$
$ΔH_{sol}. =$ Hydration energy - Lattice energy
$= - 771.7 - (-776) = + 4.3 \,kJ \,mol^{-1}$