How to calculate water vapor pressure using the Antoine equation

The Antoine equation is a mathematical formula used to estimate the vapor pressure of pure substances like water at different temperatures. It’s written as:

log⁡₁₀ P=A−B/C+T

where:

• P = vapor pressure (usually in mmHg or bar)
• T = temperature in °C
• A,B,C = constants specific to the substance

For water, one commonly used set of constants is:

A = 8.07131, B = 1730.63, C = 233.426 (valid for 1°C to 100°C).

Steps:

• Substitute the temperature (°C) into the formula.
• Calculate the right-hand side.
• Find P by taking the antilog of the result (since it’s in log₁₀ form).

Example: For water at 50°C,

log₁₀ P= 8.07131 − 1730.63 / 233.426+50 = 1.933

So P=10^1.933 =85.6 mmHg