Question 26
The enthalpy of hydration for the chloride ion is −364 kJ mol−1 and that for the bromide ion is −335 kJ mol−1.
(a) By describing the nature of the attractive forces involved, explain why the value for the enthalpy of hydration for the chloride ion is more negative than that for the bromide ion.
(3)
(b) The enthalpy of hydration for the potassium ion is −322 kJ mol−1. The lattice enthalpy of dissociation for potassium bromide is +670 kJ mol−1.
Calculate the enthalpy of solution for potassium bromide.
(2)
(c) The enthalpy of solution for potassium chloride is +17.2 kJ mol−1.
(i) Explain why the free-energy change for the dissolving of potassium chloride in water is negative, even though the enthalpy change is positive.
(3)
(ii) A solution is formed when 5.00 g of potassium chloride are dissolved in 20.0 g of water. The initial temperature of the water is 298 K.
Calculate the final temperature of the solution.
In your calculation, assume that only the 20.0 g of water changes in temperature and that the specific heat capacity of water is 4.18 J K−1 g−1.
(5)
(Total 13 marks)