Boiling Point
Normal boiling point: temperature when vapor pressure equals 1 atm. Governed by intermolecular forces and Clausius-Clapeyron. Lower P → lower BP.
Why This Chemistry Calculation Matters
Why: Boiling point depends on pressure. Normal BP at 1 atm. Distillation and high-altitude cooking rely on this relationship.
How: ln(P₂/P₁) = -(ΔHvap/R) × (1/T₂ - 1/T₁). Solve for T₂ or P₂. Temperatures in Kelvin.
- ●Water: 100°C at 1 atm; ~82°C at 0.5 atm.
- ●ΔHvap reflects intermolecular force strength.
- ●Lower pressure = lower boiling point.
- ●R = 8.314 J/(mol·K).
Boiling Point Examples
💧 Water at Sea Level
Standard atmospheric pressure
🏔️ Water at High Altitude
Lower pressure = lower boiling point
🍷 Ethanol Boiling Point
Ethanol at different pressures
📊 Pressure from Boiling Point
Calculate pressure at given temperature
⚗️ Methanol Boiling Point
Methanol vapor pressure calculation
🧪 Acetone Boiling Point
Acetone at reduced pressure
🔬 Benzene Boiling Point
Benzene vapor pressure
💨 Ammonia Boiling Point
Ammonia at different pressures
⚙️ Distillation Process
Reduced pressure distillation
🔥 High Pressure Boiling
Increased pressure increases BP
🧬 Toluene Boiling Point
Toluene vapor pressure
📝 Custom Substance
Calculate with custom values
Calculate Boiling Point
⚠️For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
Normal BP: vapor pressure = 1 atm.
— IUPAC
ln(P₂/P₁) = -(ΔHvap/R)(1/T₂ - 1/T₁).
— NIST
Water ΔHvap ≈ 40.7 kJ/mol.
— CRC
Stronger IMFs → higher BP.
— Physical chem
📋 Key Takeaways
- • ln(P₂/P₁) = -(ΔHvap/R) × (1/T₂ - 1/T₁)
- • Lower pressure = lower boiling point
- • ΔHvap = enthalpy of vaporization (kJ/mol)
- • R = 8.314 J/(mol·K)
What is the Clausius-Clapeyron Equation?
Describes how vapor pressure depends on temperature. Fundamental for phase transitions and distillation.
ln(P₂/P₁) = -(ΔHvap/R) × (1/T₂ - 1/T₁)
How to Calculate
Given T₁, P₁, P₂ and ΔHvap: solve for T₂. Or given T₁, T₂, P₁: solve for P₂. Temperatures must be in Kelvin.
When to Use
Distillation
Design reduced-pressure distillation.
High-Altitude Cooking
Understand boiling at different pressures.
Formulas
ln(P₂/P₁) = -(ΔHvap/R) × (1/T₂ - 1/T₁)
Rearrange for T₂ or P₂ as needed.
Common Substances
| Substance | Normal BP (°C) | ΔHvap (kJ/mol) |
|---|---|---|
| Water | 100 | 40.7 |
| Ethanol | 78.37 | 38.6 |
| Methanol | 64.7 | 35.2 |
| Acetone | 56.2 | 29.1 |
| Benzene | 80.1 | 30.8 |
| Toluene | 110.6 | 33.2 |
| Chloroform | 61.2 | 29.2 |
| Diethyl ether | 34.6 | 26.5 |
| Ammonia | -33.34 | 23.3 |
| Carbon tetrachloride | 76.7 | 30 |
Practical Examples
Water at 0.5 atm boils at ~82°C. Ethanol at 0.8 atm boils at ~72°C.
📚 Official Data Sources
⚠️ Disclaimer: Consult NIST and CRC for precision work.