Physical significance of temperature

[kelvin490]

Some books say when heat flows into a monatomic gas at constant volume, all of the added
energy goes into an increase in random translational molecular kinetic energy. But when the temperature is increased by the same amount in a diatomic or polyatomic gas, additional heat is needed to supply the increased rotational and vibrational energies. Thus polyatomic gases have larger molar heat capacities
than monatomic gases.

Does the absolute temperature reflect translation kinetic energy of gases only? If all types of kinetic energy of gas particles are related to temperature, why polyatomic gases have larger molar heat capacities than monatomic gases?

 

[CWatters]

Perhaps see..
http://www.Newton.dep.anl.gov/askasci/phy05/phy05161.htm

 

[kelvin490]

What confuses me, however, is that the principle of equipartition of energy says every degree of freedom contributes to 1/2 kT so total kinetic energy of diatomic molecule including rotational kinetic energy is 5/2 kT. How can we say absolute temperature relates only to translational degrees of freedom?

 

[Bystander]

when heat flows into a monatomic gas at constant volume, all of the added
energy goes into an increase in random translational molecular kinetic energy

Monatomic.

total kinetic energy of diatomic molecule including rotational kinetic energy is 5/2 kT

Diatomic.

How can we say absolute temperature relates only to translational degrees of freedom?

Because that statement is referring only to a monatomic molecule.

 

[sardar]

The physical significance of temperature is that it is a measure of the average kinetic energy of the particles in a substance. In the case of gases, this refers to the random translational motion of the gas molecules. However, in diatomic or polyatomic gases, there are additional forms of kinetic energy such as rotational and vibrational motion that contribute to the overall temperature of the gas.

When heat is added to a monatomic gas at constant volume, all of the added energy goes into an increase in random translational molecular kinetic energy. This is because monatomic gases consist of single atoms that can only move in a straight line, so their kinetic energy is solely related to their translational motion. On the other hand, when the temperature is increased by the same amount in a diatomic or polyatomic gas, additional heat is needed to supply the increased rotational and vibrational energies of the gas molecules. This is why polyatomic gases have larger molar heat capacities than monatomic gases.

In other words, the absolute temperature does reflect all types of kinetic energy of gas particles, including translational, rotational, and vibrational. However, in polyatomic gases, there are more ways for the molecules to store this kinetic energy, leading to a larger molar heat capacity. This is because polyatomic gases have more degrees of freedom, meaning they can move and rotate in more ways than monatomic gases.

In summary, while the absolute temperature reflects the average translational kinetic energy of gas particles, it also takes into account the additional forms of kinetic energy in diatomic and polyatomic gases, which contribute to their larger molar heat capacities. This is an important consideration in understanding the behavior of different types of gases at different temperatures.