Non-ideal gas

Definition

A non-ideal gas is a gas that does not follow the ideal gas law under all conditions due to interactions between molecules and the volume occupied by them. Unlike ideal gases, non-ideal gases exhibit behaviors such as compressibility and deviations from expected pressure, temperature, and volume relationships, especially at high pressures and low temperatures.

5 Must Know Facts For Your Next Test

1. Non-ideal gas behavior becomes significant at high pressures where molecular volumes can no longer be ignored and at low temperatures where intermolecular forces become stronger.
2. The Van der Waals equation introduces two parameters, 'a' for attractive forces and 'b' for molecular volume, to modify the ideal gas law for non-ideal gases.
3. Real gases can condense into liquids when subjected to high pressures and low temperatures, behaviors not predicted by the ideal gas law.
4. The compressibility factor Z provides insight into how closely a gas behaves like an ideal gas; values greater than 1 indicate repulsive interactions, while values less than 1 indicate attractive interactions.
5. For many gases, particularly those with strong intermolecular forces like water vapor, non-ideal behavior can have significant implications for thermodynamic calculations.

Review Questions

• How do the properties of non-ideal gases differ from those of ideal gases in various conditions?
  • Non-ideal gases differ from ideal gases primarily in how they respond under high pressure and low temperature conditions. While ideal gases are assumed to have no intermolecular forces and occupy no volume, non-ideal gases exhibit significant intermolecular attractions and occupy physical space. This means that as pressure increases or temperature decreases, non-ideal gases will show deviations from the expected behavior described by the ideal gas law, often leading to lower pressures than predicted.
• Discuss the significance of the Van der Waals equation in understanding non-ideal gas behavior compared to the ideal gas law.
  • The Van der Waals equation is crucial for understanding non-ideal gas behavior because it incorporates adjustments for molecular size and intermolecular attractions that are not accounted for in the ideal gas law. This equation modifies the ideal gas law by introducing two constants: 'a', which corrects for attractive forces, and 'b', which accounts for finite molecular volume. These modifications allow chemists to better predict how real gases will behave under various conditions, especially when dealing with high pressures or low temperatures.
• Evaluate how understanding non-ideal gas behavior is essential for practical applications in chemistry and engineering.
  • Understanding non-ideal gas behavior is essential because it directly impacts calculations in various chemical processes and engineering applications. For instance, in designing equipment for chemical reactions or in processes like distillation, accurate predictions of gas behavior are necessary to ensure efficiency and safety. Non-ideal behavior also affects reactions under extreme conditions where assumptions based on the ideal gas law may lead to erroneous results. Therefore, being able to account for these deviations is vital for accurate modeling and predictions in both theoretical studies and practical implementations.

Related terms

Ideal Gas Law: The equation of state for an ideal gas, given by PV=nRT, which describes the relationship between pressure (P), volume (V), temperature (T), and the number of moles (n) of a gas.

Van der Waals Equation: An equation that accounts for the volume occupied by gas molecules and the attractive forces between them, providing a more accurate description of real gas behavior compared to the ideal gas law.

Compressibility Factor (Z): A dimensionless factor that describes how much a real gas deviates from ideal gas behavior; calculated as Z = PV/nRT, where Z ≠ 1 indicates non-ideal behavior.