How To Calculate Boiling Point Elevation Constant

Boiling Point Elevation Constant Formula:

\[ K_b = \frac{R T_b^2 M_{solv}}{1000 \Delta H_{vap}} \]

Solvent Boiling Point (T_b):

Solvent Molar Mass (M_solv):

g/mol

Enthalpy of Vaporization (ΔH_vap):

J/mol

Boiling Point Elevation Constant (K_b):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Boiling Point Elevation Constant?

The boiling point elevation constant (K_b) is a colligative property constant that quantifies how much the boiling point of a solvent increases when a non-volatile solute is added. It is specific to each solvent and relates the molal concentration of solute particles to the boiling point elevation.

2. How Does the Calculator Work?

The calculator uses the boiling point elevation constant formula:

\[ K_b = \frac{R T_b^2 M_{solv}}{1000 \Delta H_{vap}} \]

Where:

\( K_b \) — Boiling point elevation constant (°C·kg/mol)
\( R \) — Gas constant (8.314 J/mol·K)
\( T_b \) — Solvent boiling point (K)
\( M_{solv} \) — Solvent molar mass (g/mol)
\( \Delta H_{vap} \) — Enthalpy of vaporization (J/mol)

Explanation: The formula derives from thermodynamic principles and relates the boiling point elevation to the solvent's physical properties.

3. Importance of K_b Calculation

Details: Knowing the boiling point elevation constant is essential for determining molecular weights of unknown solutes, calculating boiling point elevations in solutions, and understanding colligative properties in physical chemistry.

4. Using the Calculator

Tips: Enter the solvent boiling point in Kelvin, solvent molar mass in g/mol, and enthalpy of vaporization in J/mol. All values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values of K_b for common solvents?
A: Water: 0.512 °C·kg/mol, Ethanol: 1.22 °C·kg/mol, Benzene: 2.53 °C·kg/mol, Chloroform: 3.63 °C·kg/mol.

Q2: Why is the gas constant used in this formula?
A: The gas constant (R) appears because the formula derives from the Clausius-Clapeyron equation and ideal solution theory.

Q3: How does K_b relate to molality?
A: The boiling point elevation (ΔT_b) is calculated as ΔT_b = K_b × m, where m is the molality of the solution.

Q4: Can K_b be negative?
A: No, K_b is always positive since all parameters in the formula are positive values.

Q5: What units should be used for accurate calculation?
A: Consistent SI units must be used: temperature in Kelvin, molar mass in g/mol, enthalpy in J/mol, and the result will be in °C·kg/mol.