Vapor Pressure Calculator

Vapor Pressure Equation:

\[ P = P_0 \times e^{\left(\frac{-\Delta H_{vap}}{R} \times \left(\frac{1}{T} - \frac{1}{T_0}\right)\right)} \]

Initial Pressure (P₀):

kPa

Enthalpy of Vaporization (ΔH):

kJ/mol

Initial Temperature (T₀):

Temperature (T):

Vapor Pressure (P):

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1. What is Vapor Pressure?

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature. It's a measure of a substance's tendency to evaporate.

2. How Does the Calculator Work?

The calculator uses the Clausius-Clapeyron equation:

\[ P = P_0 \times e^{\left(\frac{-\Delta H_{vap}}{R} \times \left(\frac{1}{T} - \frac{1}{T_0}\right)\right)} \]

Where:

\( P \) — Vapor pressure at temperature T (kPa)
\( P_0 \) — Known vapor pressure at temperature T₀ (kPa)
\( \Delta H_{vap} \) — Enthalpy of vaporization (kJ/mol)
\( R \) — Universal gas constant (0.008314 kJ/(mol·K))
\( T \) — Temperature for which vapor pressure is calculated (K)
\( T_0 \) — Reference temperature (K)

Explanation: The equation describes how vapor pressure changes with temperature for a pure substance.

3. Importance of Vapor Pressure Calculation

Details: Vapor pressure is crucial in chemical engineering, meteorology, and industrial processes. It affects boiling points, distillation, and evaporation rates.

4. Using the Calculator

Tips: Enter all values in the specified units. Temperatures must be in Kelvin. Ensure all values are positive and temperatures are above absolute zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between vapor pressure and boiling point?
A: Boiling point is the temperature at which vapor pressure equals atmospheric pressure. Vapor pressure exists at all temperatures below boiling point.

Q2: Why must temperature be in Kelvin?
A: The equation requires absolute temperature because it's derived from thermodynamic principles where 0 represents absolute zero.

Q3: What affects enthalpy of vaporization?
A: Molecular weight, intermolecular forces, and temperature all affect ΔH_vap. It typically decreases with increasing temperature.

Q4: Is this calculator valid for all substances?
A: It works best for pure substances over limited temperature ranges. For solutions or wide temperature ranges, more complex models are needed.

Q5: How accurate is this calculation?
A: It provides reasonable estimates but assumes ΔH_vap is constant with temperature, which isn't strictly true over wide ranges.