How To Calculate Boiling Point At Different Pressures

Clausius-Clapeyron Equation:

\[ T_b = \frac{1}{\frac{1}{T_0} - \frac{R}{\Delta H_{vap}} \ln \left( \frac{P}{P_0} \right)} \]

Reference Boiling Point (T₀):

Enthalpy of Vaporization (ΔH_vap):

J/mol

Pressure (P):

Reference Pressure (P₀):

Boiling Point (T_b):

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1. What is the Clausius-Clapeyron Equation?

The Clausius-Clapeyron equation describes the relationship between vapor pressure and temperature for a substance. It allows calculation of boiling points at different pressures by relating the vapor pressure to temperature changes.

2. How Does the Calculator Work?

The calculator uses the Clausius-Clapeyron equation:

\[ T_b = \frac{1}{\frac{1}{T_0} - \frac{R}{\Delta H_{vap}} \ln \left( \frac{P}{P_0} \right)} \]

Where:

\( T_b \) — Boiling point at pressure P (K)
\( T_0 \) — Reference boiling point at pressure P₀ (K)
\( R \) — Gas constant (8.314 J/mol·K)
\( \Delta H_{vap} \) — Enthalpy of vaporization (J/mol)
\( P \) — Pressure (Pa)
\( P_0 \) — Reference pressure (Pa)

Explanation: The equation shows how boiling point changes with pressure - higher pressure increases boiling point, lower pressure decreases it.

3. Importance of Boiling Point Calculation

Details: Accurate boiling point calculation is crucial for chemical engineering processes, distillation systems, high-altitude cooking, and understanding phase behavior of substances under different pressure conditions.

4. Using the Calculator

Tips: Enter reference boiling point in Kelvin, enthalpy of vaporization in J/mol, pressure and reference pressure in Pascals. All values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: Why does boiling point change with pressure?
A: Boiling occurs when vapor pressure equals atmospheric pressure. Changing pressure changes the temperature required to reach that vapor pressure.

Q2: What are typical enthalpy of vaporization values?
A: Water has ΔH_vap ≈ 40.7 kJ/mol at 100°C. Organic solvents typically range from 20-40 kJ/mol.

Q3: How accurate is the Clausius-Clapeyron equation?
A: It provides good approximations for many substances, though it assumes constant enthalpy of vaporization and ideal gas behavior.

Q4: Can this be used for mixtures?
A: The equation is primarily for pure substances. Mixtures require more complex calculations due to varying compositions.

Q5: What units should be used for pressure?
A: Pascals (Pa) are recommended, but any consistent pressure unit can be used as long as P and P₀ use the same units.