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Difficulty: Very hardPostulates of Kinetic Theory and States of Matter

Based on the postulates of the Kinetic Molecular Theory, a gas is considered ideal when intermolecular forces are negligible and the actual volume of the gas molecules is insignificant compared to the container volume. Under high pressure and low temperature conditions, real gases deviate markedly from this ideal behavior and undergo liquefaction. Which of the following best explains the microscopic behavior of gas particles under these extreme conditions?

  1. The average kinetic energy of the molecules decreases sufficiently for intermolecular attractive forces to become dominant, while the actual volume of the gas particles becomes a significant fraction of the total container volume.Answer
  2. B
    The average kinetic energy of the molecules increases dramatically, causing collisions against container walls to become completely inelastic and resulting in rapid loss of momentum.
  3. C
    The intermolecular attractive forces completely vanish as particles draw closer together, forcing the gas volume to shrink linearly to zero at absolute zero temperature.
  4. D
    High pressure increases the speed of the gas molecules, causing repulsive forces to dominate over attractive forces and preventing condensation.

Answer

The average kinetic energy of the molecules decreases sufficiently for intermolecular attractive forces to become dominant, while the actual volume of the gas particles becomes a significant fraction of the total container volume.
According to the kinetic theory of matter, ideal gases assume no intermolecular attraction and zero molecular volume. At low temperatures, the decreased kinetic energy allows attractive forces between gas particles to overcome thermal motion. Simultaneously, at high pressures, gas particles are packed closely, making their individual volume significant relative to the total volume. These combined effects violate the ideal gas postulates and cause the gas to condense into a liquid.

Step-by-Step Solution

1
Analyze the effect of low temperature on particle kinetic energy
Decreasing temperature lowers the average kinetic energy of gas molecules (Ek∝TE_k \propto T), slowing them down.
Slower-moving molecules spend more time in proximity, allowing weak intermolecular attractive forces (Van der Waals forces) to overcome kinetic energy and pull particles together.
2
Analyze the effect of high pressure on gas particle volume
High pressure compresses the total volume of the container, forcing gas particles close together.
As the space between particles diminishes, the finite volume of the gas molecules themselves is no longer negligible relative to the reduced total container volume.
3
Synthesize the breakdown of Kinetic Molecular Theory postulates leading to liquefaction
Both key assumptions of ideal behavior (zero intermolecular forces and negligible particle volume) fail simultaneously.
The dominant attractive forces and significant molecular volume cause real gases to deviate from ideal gas laws and condense into a liquid state.

Key Concept

Deviations of Real Gases from Kinetic Molecular Theory Postulates
Estimated Time:1m 30s
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Topics

Postulates of Kinetic Theory and States of Matter