For an ideal gas, which one of the following statements does not hold true?
The speed of all gas molecules is same.
The kinetic energies of all gas molecules are not same.
The potential energy of the gas molecules is zero.
There is no interactive force between the molecules.
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC CDS-1 – 2019
A) The speed of all gas molecules is same. This is false for an ideal gas. At any given temperature, the speeds of the molecules in an ideal gas follow a distribution (like the Maxwell-Boltzmann distribution), meaning molecules have a wide range of speeds.
B) The kinetic energies of all gas molecules are not same. This is true. Since the speeds are not the same (from point A), and kinetic energy is proportional to speed squared ($KE = 1/2 mv^2$), the kinetic energies of individual molecules are also not the same. The average kinetic energy, however, is directly proportional to the absolute temperature.
C) The potential energy of the gas molecules is zero. This is true for an ideal gas. A key assumption of the ideal gas model is that there are no intermolecular forces between the molecules. Potential energy due to interparticle interactions is therefore considered zero.
D) There is no interactive force between the molecules. This is true. This is another fundamental assumption of the ideal gas model, simplifying calculations by ignoring attractions and repulsions.
The question asks which statement does *not* hold true for an ideal gas. Statement A is the one that is false for an ideal gas.
– Ideal gas molecules have no intermolecular forces.
– Potential energy due to intermolecular forces is zero in an ideal gas.