Question

Calculate the enthalpy of solution of potassium chloride if its $\Delta_{\text{L}\text{H} = 700 \text{ kJ mol}^{-1}$ and $\Delta_{\text{hyd}} \text{ H} = -680 \text{ kJ mol}^{-1}$

• A. 20 kJ mol$^{-1}$
• B. 345 kJ mol$^{-1}$
• C. 690 kJ mol$^{-1}$
• D. 1380 kJ mol$^{-1}$

Hint:

Enthalpy of solution is the sum of Lattice Enthalpy (always positive) and Hydration Enthalpy (always negative).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The enthalpy of solution is the net heat change when one mole of an ionic compound dissolves. It involves breaking the lattice and hydrating the ions.
Step 2: Key Formula or Approach:
\[ \Delta_{\text{sol}}\text{H} = \Delta_{\text{L}}\text{H} + \Delta_{\text{hyd}}\text{H} \] Note: \(\Delta_{\text{L}}\text{H}\) is energy consumed to break the lattice (positive), and \(\Delta_{\text{hyd}}\text{H}\) is energy released during solvation (negative).
Step 3: Detailed Explanation:
Given values:
\(\Delta_{\text{L}}\text{H} = +700 \text{ kJ/mol}\)
\(\Delta_{\text{hyd}}\text{H} = -680 \text{ kJ/mol}\)
\[ \Delta_{\text{sol}}\text{H} = 700 + (-680) = 20 \text{ kJ/mol} \] Step 4: Final Answer:
The enthalpy of solution is 20 kJ mol$^{-1}$.