Vapor Pressure Calculator Chemistry

Vapor Pressure Equation:

\[ P = P^* \times \exp\left(\frac{\Delta H_{vap}}{R} \left(\frac{1}{T_b} - \frac{1}{T}\right)\right) \]

Reference Pressure (P*):

atm

Enthalpy of Vaporization (ΔH_vap):

J/mol

Boiling Point (T_b):

Temperature (T):

Vapor Pressure (P):

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1. What is the Vapor Pressure Equation?

The vapor pressure equation calculates the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. It's derived from the Clausius-Clapeyron relation and is important in chemistry and chemical engineering.

2. How Does the Calculator Work?

The calculator uses the vapor pressure equation:

\[ P = P^* \times \exp\left(\frac{\Delta H_{vap}}{R} \left(\frac{1}{T_b} - \frac{1}{T}\right)\right) \]

Where:

\( P \) — Vapor pressure (atm)
\( P^* \) — Reference pressure (atm)
\( \Delta H_{vap} \) — Enthalpy of vaporization (J/mol)
\( T_b \) — Boiling point temperature (K)
\( T \) — Current temperature (K)
\( R \) — Universal gas constant (8.314 J/mol·K)

Explanation: The equation shows how vapor pressure changes with temperature based on the substance's heat of vaporization.

3. Importance of Vapor Pressure Calculation

Details: Vapor pressure is crucial for understanding evaporation rates, boiling points, and the volatility of substances. It's essential in distillation, drying processes, and predicting environmental fate of chemicals.

4. Using the Calculator

Tips: Enter all values in the correct units. The reference pressure is typically the vapor pressure at the boiling point (often 1 atm). All temperatures must be in Kelvin.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between P and P*?
A: P* is the reference vapor pressure (usually at boiling point), while P is the vapor pressure at your temperature of interest.

Q2: How do I convert Celsius to Kelvin?
A: Add 273.15 to the Celsius temperature to get Kelvin.

Q3: Where can I find ΔH_vap values?
A: These are typically found in chemical handbooks or thermodynamic tables for specific substances.

Q4: What are typical vapor pressure values?
A: Vapor pressure ranges from near 0 for non-volatile substances to 1 atm at boiling point for many liquids.

Q5: Is this equation valid for all temperatures?
A: It works best near the boiling point. For wider temperature ranges, more complex equations like Antoine equation may be better.