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May 23, 2024
Van Der Waals Equation

The Van der Waals equation provides a valuable tool for describing and understanding the behavior of real gases under conditions where the ideal gas law falls short. It has applications in diverse scientific and industrial fields, contributing to our understanding of gas properties and facilitating the design and operation of processes involving gases.

वैन डेर वाल्स समीकरण उन परिस्थितियों में वास्तविक गैसों के व्यवहार का वर्णन करने और समझने के लिए एक मूल्यवान उपकरण प्रदान करता है जहां आदर्श गैस कानून कम पड़ता है। इसमें विविध वैज्ञानिक और औद्योगिक क्षेत्रों में अनुप्रयोग हैं,

जो गैस गुणों की हमारी समझ में योगदान देता है और गैसों से जुड़ी प्रक्रियाओं के डिजाइन और संचालन को सुविधाजनक बनाता है।

Van Der Waals Equation


Importance in Real-world Applications:

  • Industry: The Van der Waals equation is applied in chemical engineering for the design and optimization of processes involving gases.
  • Environmental Science: It aids in understanding gas behavior in various environmental conditions.
  • Cryogenics: When dealing with gases at extremely low temperatures, the Van der Waals equation becomes crucial.

Van der Waals Equation:

    • Empirical Nature: this equation is empirical and specific to each gas. Constants and must be determined experimentally.
    • Does Not Capture All Behavior: While the Van der Waals equation improves upon the ideal gas law, it still does not account for all complexities of real gases. For instance, it neglects molecular repulsions at short distances.
  • Reduced Variables: Scientists often use reduced variables (dimensionless quantities) to express this equation more universally. For example, the reduced pressure () and reduced temperature () allow for comparisons between different gases.
  • Van der Waals Isotherms: These are graphical representations of this equation, showing the relationship between pressure and volume at constant temperature. Isotherms exhibit behavior such as the presence of a critical point,

1. Ideal Gas Law and Its Limitations:

The ideal gas law, PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature, provides a simple and convenient model for describing the behavior of gases under many conditions.

However, it has limitations, especially at high pressures and low temperatures, where real gases deviate significantly from ideal behavior.

2. Deviations from Ideal Behavior:

Real gases differ from the ideal gas behavior due to two main factors: the finite size of gas molecules and intermolecular forces (attractions and repulsions) between them.

The ideal gas law assumes that gas molecules have no volume and do not interact with each other, which is not the case for real gases.

3. Van der Waals Equation:

The Van der Waals equation was developed to correct the shortcomings of the ideal gas law. It is expressed as:



  • is the pressure.
  • is the volume.
  • is the number of moles.
  • is the ideal gas constant.
  • is the temperature.
  • and are Van der Waals constants specific to each gas.

The term  accounts for the attractive forces between molecules, and adjusts for the volume occupied by the gas molecules.

4. Physical Significance of Van der Waals Constants:

: Represents the strength of intermolecular attraction. The larger the value, the stronger the attractive forces, and the more likely the gas will deviate from ideal behavior.

: Represents the volume occupied by one mole of gas molecules. It corrects for the finite size of gas molecules.

5. Application and Interpretation:

  • Deviation from Ideal Gas Behavior: The Van der Waals equation is particularly useful when dealing with gases under conditions where the ideal gas law fails. For example, at high pressures or low temperatures, where the volume occupied by gas molecules and intermolecular attractions become significant.
  • Critical Phenomena: The Van der Waals equation helps in understanding critical phenomena, such as the critical temperature and critical pressure, where a gas can exist as both a liquid and a vapor.


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