Which statements are correct about degrees of freedom?
(A) A molecule with n degrees of freedom has n2 different ways of storing energy.
(B) Each degree of freedom is associated with (1/2)RT average energy per mole.
(C) A monatomic gas molecule has 1 rotational degree of freedom whereas diatomic molecule has 2 rotational degrees of freedom.
(D) CH4 has a total of 6 degrees of freedom.
Choose the correct answer from the option given below:
Which statements are correct about degrees of freedom?
(A) A molecule with n degrees of freedom has n2 different ways of storing energy.
(B) Each degree of freedom is associated with (1/2)RT average energy per mole.
(C) A monatomic gas molecule has 1 rotational degree of freedom whereas diatomic molecule has 2 rotational degrees of freedom.
(D) CH4 has a total of 6 degrees of freedom.
Choose the correct answer from the option given below:
- (B) and (C) only
- (B) and (D) only
- (A) and (B) only
- (C) and (D) only
The Correct Option is B
Solution and Explanation
The correct answer is (B) : (B) and (D) only
Statement A is incorrect, statement B is correct by equipartition of energy. Statement C is incorrect as monoatomic does not have any rotational degree of freedom and CH4 is a polyatomic gas so it has 6 degree of freedom.
So only B and D are correct.
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Concepts Used:
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Postulates of Kinetic Theory of Gases:
- Gases consist of particles in constant, random motion. They continue in a straight line until they collide with each other or the walls of their container.
- Particles are point masses with no volume. The particles are so small compared to the space between them, that we do not consider their size in ideal gases.
- Gas pressure is due to the molecules colliding with the walls of the container. All of these collisions are perfectly elastic, meaning that there is no change in energy of either the particles or the wall upon collision. No energy is lost or gained from collisions. The time it takes to collide is negligible compared with the time between collisions.
- The kinetic energy of a gas is a measure of its Kelvin temperature. Individual gas molecules have different speeds, but the temperature and
kinetic energy of the gas refer to the average of these speeds. - The average kinetic energy of a gas particle is directly proportional to the temperature. An increase in temperature increases the speed in which the gas molecules move.
- All gases at a given temperature have the same average kinetic energy.
- Lighter gas molecules move faster than heavier molecules.
