Calculate The Vapor Pressure of Water at 80 Degrees Celsius

The vapor pressure of water at 80°C is approximately 1.013 bar. This calculator uses the Antoine equation to determine vapor pressure based on temperature. The Antoine equation is widely used in chemical engineering and thermodynamics to estimate vapor pressures of pure substances.

How to calculate vapor pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (liquid or solid) at a given temperature in a closed system. For water, vapor pressure increases with temperature.

To calculate the vapor pressure of water at a specific temperature, you can use the Antoine equation, which relates vapor pressure to temperature. The equation is:

log₁₀(P) = A - (B / (T + C))

Where:

P = vapor pressure (in mmHg or bar)
T = temperature (in °C)
A, B, C = Antoine equation constants for water

The Antoine constants for water are typically:

A = 8.07131
B = 1730.63
C = 233.426

For 80°C, the calculation would be:

Convert the temperature to Kelvin if needed (though Antoine uses °C)
Plug the values into the equation
Calculate the logarithm
Convert the result to the desired pressure unit

The Antoine equation

The Antoine equation is an empirical relationship that provides a good approximation of vapor pressure for many pure substances over a range of temperatures. It's commonly used in chemical engineering and thermodynamics.

log₁₀(P) = A - (B / (T + C))

Where:

P = vapor pressure (in mmHg or bar)
T = temperature (in °C)
A, B, C = Antoine equation constants

The Antoine constants vary depending on the substance and the temperature range. For water, the constants are typically:

A = 8.07131
B = 1730.63
C = 233.426

This equation is valid for temperatures between 0°C and 100°C for water.

Example calculation

Let's calculate the vapor pressure of water at 80°C using the Antoine equation.

Given:

Temperature (T) = 80°C
Antoine constants for water:

A = 8.07131
B = 1730.63
C = 233.426

Step 1: Plug the values into the Antoine equation:

log₁₀(P) = 8.07131 - (1730.63 / (80 + 233.426))

Step 2: Calculate the denominator:

80 + 233.426 = 313.426

Step 3: Divide B by the denominator:

1730.63 / 313.426 ≈ 5.523

Step 4: Subtract from A:

8.07131 - 5.523 ≈ 2.548

Step 5: Convert from log₁₀ scale to linear scale:

P = 10²·⁵⁴⁸ ≈ 363.6 mmHg

Step 6: Convert to bar (1 bar = 750.062 mmHg):

363.6 / 750.062 ≈ 0.4846 bar

The vapor pressure of water at 80°C is approximately 0.4846 bar.

Frequently asked questions

What is the Antoine equation used for?: The Antoine equation is used to estimate the vapor pressure of pure substances based on temperature. It's widely used in chemical engineering and thermodynamics.
What are the Antoine constants for water?: The Antoine constants for water are typically A = 8.07131, B = 1730.63, and C = 233.426 for temperatures between 0°C and 100°C.
How accurate is the Antoine equation for water?: The Antoine equation provides a good approximation for water vapor pressure over a range of temperatures, but it's not as precise as experimental data for specific conditions.
Can I use the Antoine equation for other substances?: Yes, the Antoine equation can be used for many pure substances, but the constants (A, B, C) will vary depending on the substance and temperature range.
What units does the Antoine equation use?: The Antoine equation typically uses temperature in °C and vapor pressure in mmHg, but can be converted to other units as needed.