Skip to content
GK24
Prime
General ScienceHard

Which of the following is NOT a postulate of the kinetic theory of gases?

  1. A.Gas molecules are in constant random motion
  2. B.Collisions between gas molecules are perfectly elastic
  3. C.Gas molecules attract one another strongly at all times
  4. D.The volume of the molecules is negligible compared with the volume of the container

Correct answer

C. Gas molecules attract one another strongly at all times

Explanation

The correct answer is C, gas molecules attract one another strongly at all times. The kinetic theory of an ideal gas assumes exactly the opposite: that there are no forces of attraction or repulsion between molecules except during the brief moment of a collision. It is this assumption that fails for real gases, and van der Waals added a pressure correction term to the ideal gas equation precisely to account for intermolecular attraction. A, constant random motion is the first postulate, and it explains both pressure and diffusion. B, perfectly elastic collisions is a postulate as well, and it is what keeps the total kinetic energy, and hence the temperature, constant in an isolated container. D, the negligible volume of molecules is another postulate, and its failure at high pressure is corrected by van der Waals through the volume term. Questions of this kind usually hide the real-gas property among the ideal-gas postulates.

Read the full article: Gas Laws and Kinetic Theory of Gases: Formulas and PYQs

Practice Questions

View all
Q1.General ScienceEasy

Boyle's law states that at constant temperature, the volume of a fixed mass of gas is

  1. A.Directly proportional to its pressure
  2. B.Inversely proportional to its pressure
  3. C.Independent of its pressure
  4. D.Proportional to the square of its pressure
Show answer
Correct answer: B. Inversely proportional to its pressure

Boyle's law, established in 1662, says that for a fixed mass of gas at constant temperature the product of pressure and volume stays constant, so doubling the pressure halves the volume.

Q2.General ScienceEasy

A hot air balloon rises because warm air

  1. A.Becomes denser than the surrounding air
  2. B.Expands and becomes less dense than the surrounding air
  3. C.Loses its mass on heating
  4. D.Has a lower specific heat than cold air
Show answer
Correct answer: B. Expands and becomes less dense than the surrounding air

By Charles's law the volume of a fixed mass of gas at constant pressure is proportional to its absolute temperature, so heating the air inside the envelope makes it expand; some of it escapes from the open mouth, the mass of air left inside falls, its density becomes lower than…

Q3.General ScienceEasy

Absolute zero of temperature is equal to

  1. A.0 degrees Celsius
  2. B.-100 degrees Celsius
  3. C.-273.15 degrees Celsius
  4. D.-373.15 degrees Celsius
Show answer
Correct answer: C. -273.15 degrees Celsius

Extending the straight line of Charles's law backwards shows that the volume of an ideal gas would become zero at minus 273.15 degrees Celsius, and this point is taken as the zero of the kelvin or absolute scale, at which molecular motion carries its least possible energy.

Q5.General ScienceMedium

The volume occupied by one mole of an ideal gas at 273.15 K and one atmosphere pressure is about

  1. A.11.2 litres
  2. B.22.4 litres
  3. C.44.8 litres
  4. D.1 litre
Show answer
Correct answer: B. 22.4 litres

Substituting one mole, 273.15 kelvin and one atmosphere in the ideal gas equation gives a volume of 22.4 litres, the molar volume at standard temperature and pressure, and this is the figure used in mole calculations; with the modern standard pressure of one bar the value works out to about…