Physical significance of temperature

In summary: For a diatomic or polyatomic molecule, additional heat is needed to supply the increased rotational and vibrational energies, resulting in a larger molar heat capacity. The principle of equipartition of energy states that every degree of freedom contributes to 1/2 kT, so the total kinetic energy of a diatomic molecule includes both translational and rotational energy. This explains why polyatomic gases have larger molar heat capacities than monatomic gases. In summary, when heat is added to a monatomic gas at constant volume, all of the added energy goes into an increase in translational kinetic energy. However, in diatomic or polyatomic gases, additional heat is needed to supply the increased rotational and vibrational energies, resulting in a larger m
  • #1

kelvin490

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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?
 
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  • #3
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?
 
  • #4
kelvin490 said:
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.

kelvin490 said:
total kinetic energy of diatomic molecule including rotational kinetic energy is 5/2 kT
Diatomic.
kelvin490 said:
How can we say absolute temperature relates only to translational degrees of freedom?
Because that statement is referring only to a monatomic molecule.
 
  • #5


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.
 

1. What is the physical significance of temperature?

The physical significance of temperature is its ability to measure the average kinetic energy of particles in a substance. It is a fundamental property of matter and is closely related to the amount of heat energy present in a system.

2. How is temperature measured?

Temperature can be measured using a thermometer, which contains a temperature-sensitive material such as mercury or alcohol. The material expands or contracts in response to temperature changes, allowing us to read the temperature on a calibrated scale.

3. What is the difference between temperature and heat?

Temperature and heat are often used interchangeably, but they are actually two distinct concepts. Temperature is a measure of the average kinetic energy of particles, while heat is the transfer of thermal energy from a hotter object to a cooler object.

4. How does temperature affect matter?

Temperature affects matter in many ways. As temperature increases, the kinetic energy of particles also increases, causing them to vibrate faster and take up more space. This can lead to changes in state, such as melting or boiling, as well as changes in chemical reactions and physical properties.

5. What is absolute zero?

Absolute zero is the theoretical lowest possible temperature, at which all molecular motion ceases. It is typically measured as 0 Kelvin or -273.15 degrees Celsius. At this temperature, all matter would be in a solid state and no heat energy would be present in a system.

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