Vapor Pressure Calculation Formula

Raoult's Law Formula:

\[ P = \gamma \times x \times P_{sat} \]

Activity Coefficient (γ):

dimensionless

Mole Fraction (x):

dimensionless

Saturation Pressure (P_sat):

atm

Vapor Pressure (P):

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1. What is Raoult's Law?

Raoult's law states that the vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution. It's a fundamental law in thermodynamics and physical chemistry.

2. How Does the Calculator Work?

The calculator uses the modified Raoult's law formula:

\[ P = \gamma \times x \times P_{sat} \]

Where:

\( P \) — Vapor pressure of the solution (atm)
\( \gamma \) — Activity coefficient (dimensionless)
\( x \) — Mole fraction of the component (dimensionless)
\( P_{sat} \) — Saturation vapor pressure of the pure component (atm)

Explanation: The activity coefficient accounts for non-ideal behavior in real solutions, modifying the ideal Raoult's law.

3. Importance of Vapor Pressure Calculation

Details: Vapor pressure calculations are crucial for designing distillation columns, predicting evaporation rates, and understanding phase equilibria in chemical engineering processes.

4. Using the Calculator

Tips: Enter the activity coefficient (γ ≥ 1 for positive deviation, γ ≤ 1 for negative deviation), mole fraction (0 ≤ x ≤ 1), and saturation pressure of the pure component. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: When does Raoult's law apply exactly?
A: Raoult's law applies exactly to ideal solutions where intermolecular forces between different components are equal to those between like components.

Q2: What does the activity coefficient represent?
A: The activity coefficient (γ) accounts for deviations from ideal behavior. γ = 1 for ideal solutions, >1 for positive deviations, and <1 for negative deviations.

Q3: Can this be used for multi-component mixtures?
A: This calculator is for binary systems. For multi-component systems, you would need to calculate partial pressures for each component and sum them.

Q4: What are typical values for activity coefficients?
A: Activity coefficients typically range from 0.5 to 2.0 for most common solutions, but can be higher for highly non-ideal systems.

Q5: How does temperature affect vapor pressure?
A: Temperature primarily affects P_sat through the Antoine equation or similar correlations. The activity coefficient may also vary with temperature.