Consider the given data : (a) HCl(g) + 10H2O(l) HCl 10H2O; H = -69.01 kJ mol-1 (b) HCl(g) + 40H2O(l) HCl 40H2O; H = -72.79 kJ mol-1 Choose the correct statement :
- The heat of dilution for the HCl (HCl 10H2O to HCl 40H2O) is 3.78 kJ mol-1.
- Dissolution of gas in water is an endothermic process.
- The heat of solution depends on the amount of solvent.
- The heat of formation of HCl solution is represented by both (a) and (b).
Answer
(3) The heat of solution depends on the amount of solvent.
Solution
(1) (b) – (a): HCl 10H2O + 30H2O HCl 40H2O
Hdil = -72.79 - (-69.01) = -3.78 kJ mol-1
Heat of dilution is -3.78 kJ mol-1 (heat is released), not +3.78 kJ mol-1. Incorrect.
(2) Both ΔH values are negative dissolution of HCl gas in water is exothermic. Incorrect.
(3) ΔH changes from -69.01 to -72.79 kJ mol-1 when the amount of water changes from 10 to 40 mol heat of solution depends on the amount of solvent. Correct.
(4) Heat of formation refers to formation from elements ( 12H2 + 12Cl2), not from HCl(g); (a) and (b) are enthalpies of solution. Incorrect.
Answer: (3)