Question

Define molal depression constant. How is it related to enthalpy of fusion?

Hint:

Molal depression constant helps determine freezing point depression. It depends on the solvent properties, including its enthalpy of fusion and molar mass.

Answer 1

Step 1: Definition of Molal Depression Constant Molal depression constant (\( K_f \)) is the depression in freezing point observed when one mole of a non-volatile solute is dissolved in 1 kg (1000 g) of solvent. Step 2: Relationship with Enthalpy of Fusion The molal depression constant is mathematically expressed as: \[ K_f = \frac{R \times M_{\text{solvent}} \times T_f^0}{1000 \times \Delta_{\text{fus}} H^0} \] where:
- \( R \) is the universal gas constant,
- \( M_{\text{solvent}} \) is the molar mass of the solvent,
- \( T_f^0 \) is the freezing point of the pure solvent,
- \( \Delta_{\text{fus}} H^0 \) is the enthalpy of fusion of the solvent.