Calculate The Molal Boiling Point Elevation Constant

Molal Boiling Point Elevation Constant Formula:

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

Boiling Point (T_b):

Solvent Molar Mass (M_solv):

g/mol

Enthalpy of Vaporization (ΔH_vap):

J/mol

Molal Boiling Point Elevation Constant (K_b):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Molal Boiling Point Elevation Constant?

The molal boiling point elevation constant (K_b) is a property of a solvent that quantifies how much the boiling point of the solvent increases when a non-volatile solute is added. It represents the boiling point elevation per molal concentration of solute particles.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

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

Explanation: This equation relates the boiling point elevation constant to fundamental thermodynamic properties of the solvent.

3. Importance of K_b Calculation

Details: 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 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 constant molal rather than molar?
A: Boiling point elevation depends on the number of solute particles per mass of solvent (molality), not per volume of solution (molarity).

Q3: Does K_b depend on temperature?
A: Yes, K_b is temperature-dependent as it involves the square of the boiling point temperature.

Q4: What are the limitations of this calculation?
A: The formula assumes ideal solution behavior and that the solute is non-volatile and non-electrolytic.

Q5: How is K_b used in practical applications?
A: It's used to determine molecular weights of unknown compounds and to calculate boiling point elevations in various industrial processes.