Question

The diagram below shows the energy changes that occur when sodium chloride dissolves in water. Study it and answer the questions that follow.

1. What do ∆H1, ∆H2 and ∆H3 represent? 
2. Given that the lattice energy of NaCl (s) is -776 kJmol^-1 and hydration energies of Na⁺(g) and Cl^-(g) are -407 kJmol^-1 and -364 kJmol^-1 respectively. Calculate the heat of solution (∆Hsol) of 1 mole NaCl (s). 

Answer 1

1.   
   • ∆H1 : Lattice energy
   • ∆H2 : Hydration energy
   • ∆H3 :Heat of solution
2.    
   • (∆Hsol) = ∆H1 + ∆H2
     = 776 + (-407-364) = + 5 kJmol^-1