Critical Pressure Formula:
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Definition: Critical pressure is the minimum pressure required to liquify a substance at its critical temperature.
Purpose: This calculator determines the critical pressure using the Redlich-Kwong equation parameters a and b.
The calculator uses the formula:
Where:
Explanation: The formula derives from the Redlich-Kwong equation of state and relates the critical pressure to the equation parameters.
Details: Critical pressure is essential for understanding phase behavior, designing chemical processes, and working with real gases.
Tips: Enter the Redlich-Kwong parameters a and b (must be positive values). The calculator uses the universal gas constant automatically.
Q1: What are typical values for parameters a and b?
A: These vary by substance. For example, water has a ≈ 142.59 and b ≈ 0.0211 in appropriate units.
Q2: Why is the universal gas constant included?
A: The Redlich-Kwong equation relates to thermodynamic properties, requiring the gas constant for dimensional consistency.
Q3: What units should I use for parameters a and b?
A: Use consistent units that match the gas constant (J/mol·K). The calculator will output pressure in Pascals.
Q4: Can I use this for any gas?
A: Yes, as long as you have the correct Redlich-Kwong parameters for that specific gas.
Q5: How accurate is this calculation?
A: It provides theoretical critical pressure based on the Redlich-Kwong model, which is more accurate for real gases than ideal gas law.