All calculatorsBoiling Point at Altitude Calculator
Estimate the boiling point at a given altitude or ambient pressure. Choose Water (Antoine) or a custom liquid (Clausius–Clapeyron). See steps and a mini chart.
Background
A liquid boils when its saturation vapor pressure equals the ambient pressure. With altitude, atmospheric pressure drops, so boiling temperature decreases. This tool uses the standard atmosphere to convert altitude→pressure (0–11 km), the Antoine equation for water’s saturation pressure (1–100 °C), and the Clausius–Clapeyron relation for custom liquids.
How this calculator works
- Convert altitude h to pressure with the standard atmosphere (0–11 km): P = P₀ (1 − Lh/T₀)gM/(RL).
- Water mode: use Antoine: log₁₀ P(mmHg) = A − B/(C + T(°C)) → invert for T.
- Custom mode: Clausius–Clapeyron: ln(P₂/P₁) = −ΔHᵥₐₚ/R (1/T₂ − 1/T₁) with P₁ = 1 atm at the normal boiling point T₁, solve for T₂ at ambient P₂.
Formula & Equation Used
Standard atmosphere (0–11 km): P = P₀ (1 − Lh/T₀)gM/(RL)
Antoine (water, 1–100 °C): log₁₀ P(mmHg) = 8.07131 − 1730.63/(233.426 + T(°C))
Clausius–Clapeyron: ln(P₂/P₁) = −ΔHᵥₐₚ/R (1/T₂ − 1/T₁)
Example Problems & Step-by-Step Solutions
Example 1 — Boiling point of water in Denver
h ≈ 1609 m → P ≈ 83.3 kPa. Antoine inversion gives T ≈ 94.6 °C.
Example 2 — Ethanol at 2000 m
T₁ = 78.37 °C (351.52 K) at 1 atm; ΔHᵥₐₚ ≈ 38.6 kJ·mol⁻¹; P(2000 m) ≈ 79.5 kPa.
ln(P₂/P₁) = −ΔHᵥₐₚ/R(1/T₂ − 1/T₁) → T₂ ≈ 73.7 °C.
Example 3 — Water at 90 kPa
P = 90 kPa → 675 mmHg. Antoine inversion gives T ≈ 96.7 °C.
Frequently Asked Questions
Q: Does humidity or weather matter?
This calculator uses the standard atmosphere. Real weather can shift pressure a bit, changing Tb by ~±0.2–0.5 °C.
Q: Why Antoine only for water?
Water’s Antoine constants are standard and accurate in 1–100 °C. For other liquids, reliable constants vary; we use Clausius–Clapeyron with ΔHᵥₐₚ.
Q: What if I already know local pressure?
Enter it directly (mmHg, kPa, or atm). It overrides altitude.
