1. What is Relative Lowering of Vapour Pressure?

Definition: The Relative Lowering of Vapour Pressure is the lowering of vapour pressure of pure solvent on addition of solute.

Purpose: This calculator helps determine how much the vapour pressure of a solvent decreases when a solute is added, based on boiling point elevation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RLVP \) — Relative Lowering of Vapour Pressure
• \( \Delta H_{vap} \) — Molar Enthalpy of Vaporization (J/mol)
• \( \Delta T_b \) — Boiling Point Elevation (K)
• \( R \) — Universal gas constant (8.314 J/mol·K)
• \( T_{bp} \) — Solvent boiling point (K)

Explanation: The formula relates the boiling point elevation to the relative lowering of vapour pressure through thermodynamic principles.

3. Importance of This Calculation

Details: Understanding vapour pressure lowering is crucial for colligative properties studies, industrial processes, and solution chemistry.

4. Using the Calculator

Tips: Enter the molar enthalpy of vaporization (default 40700 J/mol), boiling point elevation (default 0.99 K), and solvent boiling point (default 15 K). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is typical molar enthalpy of vaporization for water?
A: For water at 100°C, it's approximately 40.7 kJ/mol (40700 J/mol).

Q2: How does boiling point elevation relate to vapour pressure?
A: Adding solute lowers vapour pressure, which requires higher temperature to boil (elevation).

Q3: What units should I use?
A: Use consistent SI units: Joules for energy, Kelvin for temperature.

Q4: Can I use this for any solvent?
A: Yes, as long as you have the correct parameters for your solvent.

Q5: Why is the boiling point squared in the formula?
A: This comes from the thermodynamic derivation relating these properties.