The real gases show deviation from ideal behaviour at:

Correct answer: C. Low temperature and high pressure

  • A. Low temperature and low pressure
  • B. High temperature and high pressure
  • C. Low temperature and high pressure
  • D. High temperature and low pressure

Explanation

Deviation from ideal gas behavior occurs primarily under high pressure and low temperature conditions. At high pressures, gas molecules are forced closer together, making the volume of the gas significantly less than predicted by the ideal gas law due to the finite volume of the molecules and intermolecular interactions. Conversely, at low temperatures, the kinetic energy of gas molecules decreases, enhancing the influence of intermolecular forces, which can lead to condensation into liquids. These factors highlight that real gases do not always follow the ideal gas law, especially near their boiling points or under conditions close to liquefaction, necessitating more complex equations of state, such as the van der Waals equation, to better describe their behavior.

This question appeared on the UHS MDCAT 2024 paper, which you can sit online with every answer explained.

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About Real and Ideal Gases

An ideal gas is modelled as particles with negligible volume and no intermolecular attraction, obeying Boyle's, Charles's and Avogadro's laws through PV = nRT. Real gases deviate from this behaviour, especially at high pressure and low temperature, because particle volume and attractive forces matter; the van der Waals equation explains these corrections.

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