1. What is Van der Waals Constant a?

Definition: Van der Waals constant 'a' represents the magnitude of attractive forces between gas molecules. It corrects the ideal gas law for intermolecular forces.

Purpose: This calculator determines the 'a' constant based on the critical temperature and 'b' constant of a gas.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( a \) — Van der Waals constant (Pa·m⁶/mol²)
• \( b \) — Van der Waals constant (m³/mol)
• \( R \) — Universal gas constant (8.314 J/mol·K)
• \( T_c \) — Critical temperature (K)

Explanation: The formula relates the constants at the critical point where the distinction between gas and liquid phases disappears.

3. Importance of Van der Waals Constants

Details: These constants are crucial for accurate gas behavior predictions, especially at high pressures and low temperatures where real gases deviate from ideal behavior.

4. Using the Calculator

Tips: Enter the Van der Waals constant b (m³/mol) and critical temperature (K). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for Van der Waals constant b?
A: For common gases, b ranges from about 3 × 10⁻⁵ m³/mol (He) to 5 × 10⁻⁵ m³/mol (larger molecules like CO₂).

Q2: What is critical temperature?
A: The highest temperature at which a gas can be liquefied by pressure alone. Above this temperature, no amount of pressure can liquefy the gas.

Q3: Why is the universal gas constant used?
A: R appears in the derivation of the Van der Waals equation from the critical point conditions.

Q4: What units does this calculator use?
A: SI units are used throughout (m³, mol, K, Pa) for consistency with standard physical chemistry practice.

Q5: How accurate is this calculation?
A: This provides theoretical values based on critical point conditions. Experimental values may differ slightly.