Moderate

The behaviour of a real gas is usually depicted by plotting compressibility factor Z versus P at a constant temperature. At high temperatures and high pressure, Z is usually more than one. This fact can be explained by van der Waals equation when:

Correct answer: A. the constant 'a' is negligible and not 'b'

  • A. the constant 'a' is negligible and not 'b'
  • B. the constant 'b' is negligible and not 'a'
  • C. both constants 'a' & 'b' are negligible
  • D. both the constants 'a' & 'b' are not negligible

Explanation

At low pressure, b can be ignored as the volume of the gas is very high. At high temperature, a can be ignored as the pressure of the gas is high. Solution is given below.

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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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