Question

Which is not true about the Kinetic Molecular Theory?
A. Gas molecules have forces of attraction for each other.
B. Gas molecules move in a random, straight line motion.
C. Gas molecules have a negligible volume compared to the volume they occupy.
D. Collisions between gas molecules lead to a transfer of energy that is conserved.
E. All of the above statements are correct.

Answer 1

Hint: The Kinetic Molecular Theory describes a gas as a collection of the large number of identical submicroscopic particles (atoms or molecules), all of which are in constant, rapid, random motion. Their size is assumed to be much smaller than the average distance between the particles. The particles undergo random elastic collisions between themselves and with the enclosing walls of the container.

Complete step by step answer:
According to the Kinetic Molecular Theory, there are salient features that determine the property of the gases. The various assumptions made by this theory are:
(i) The gas consists of very small particles that are known as molecules. Their size is such that the total volume of the individual gas molecules added up is negligible compared to the volume of the smallest open ball containing all the molecules. This is equivalent to stating that the average distance separating the gas particles is large compared to their size.
(ii) These particles have the same mass.
(iii) The number of molecules is so large that statistical treatment can be applied.
(iv) The rapidly moving particles constantly collide among themselves and with the walls of the container. All these collisions are perfectly elastic. This means the molecules are considered to be perfectly spherical in shape and elastic in nature.
(v) Except during collisions, the interactions among molecules are negligible.
(vi) The average kinetic energy of the gas particles depends only on the absolute temperature of the system. The kinetic theory has its own definition of temperature, not identical with the thermodynamic definition.
(vii) The elapsed time of a collision between a molecule and the container's wall is negligible when compared to the time between successive collisions.
(viii) Because they have mass, gravity will accelerate molecules.
Based on the above assumptions, the correct option is: A. Gas molecules have forces of attraction for each other.

So, the correct answer is “Option A”.

Note:
More modern developments relax these assumptions and are based on the Boltzmann equation. These can accurately describe the properties of dense gases, because they include the volume of the molecules. The necessary assumptions are the absence of quantum effects, molecular chaos and small gradients in bulk properties. Expansions to higher orders in the density are known as virial expansions.