Question
Question: One mole of anhydrous MgCl2 dissolves in water and librates 25 cal/mol of heat. \(\Delta\)Hhydration...
One mole of anhydrous MgCl2 dissolves in water and librates 25 cal/mol of heat. ΔHhydration of MgCl2 = –30 cal/mol. Heat of dissolution of MgCl2.H2O is
A
+5 cal/mol
B
–5 cal/mol
C
55 cal/mol
D
–55 cal/mol
Answer
+5 cal/mol
Explanation
Solution
MgCl2.H2O ⟶ MgCl2(aq) ΔH1 = ?
MgCl2(aq) ⟶ Mg2+(aq) + 2Cl–(aq) ΔH2 = –30 cal/mol
MgCl2 (s) ⟶ Mg2+(aq) + 2Cl– (aq) ΔH3 = – 25 cal/mol
ΔH1 + ΔH2 = ΔH3
ΔH1 = ΔH3 – ΔH2 = –25 + 30 = + 5 cal/mol.