How to Calculate Vapor Pressure
What is Vapor Pressure?
Vapor pressure increases exponentially with temperature (Clausius-Clapeyron): ln(P₂/P₁) = -ΔH_vap/R × (1/T₂ - 1/T₁).
Step-by-Step Guide
- 1Input substance, temperature(s), enthalpy of vaporization
- 2Calculate vapor pressure
- 3Predict boiling point
Worked Examples
Input
Water at 25°C: P = 23.8 mmHg
Result
At 100°C: P = 760 mmHg (boiling point)
Common Mistakes to Avoid
- ✕Using Clausius-Clapeyron beyond valid range
- ✕Not assuming constant ΔH_vap
Frequently Asked Questions
What's normal boiling point?
Temperature where vapor pressure equals 1 atm; varies with atmospheric pressure.
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