Internal energy of a substance.

[shenjie]

Hi all, I was taught that internal energy of an ideal gas in depending on the temperature which mean during isothermal process, the change in internal energy is equal to zero. Is this statement true?

How about the change in the internal energy of a substance when it is condensed from saturated vapour to saturated liquid isothermally?

Sincerely thanks to those who help me :)

 

[Chestermiller]

Hi all, I was taught that internal energy of an ideal gas in depending on the temperature which mean during isothermal process, the change in internal energy is equal to zero. Is this statement true?

Yes.

How about the change in the internal energy of a substance when it is condensed from saturated vapour to saturated liquid isothermally?

No. During the condensation, it is not an ideal gas. It's part vapor and part liquid.

 

[hilbert2]

Hi all, I was taught that internal energy of an ideal gas in depending on the temperature which mean during isothermal process, the change in internal energy is equal to zero. Is this statement true?

That's true for an ideal gas, but in real gases there's a slight dependence of internal energy on volume, i.e. the partial derivative $\left(\frac{\partial U}{\partial V}\right)_{T,n}$ is not exactly zero. This is related to the Joule-Thomson effect.

 

[BruceW]

yeah, for a 'true' ideal gas, the internal energy only depends on the temperature (assuming the number of molecules is constant). I think some people call this 'true' ideal gas a 'perfect' gas.

 

[PJC01]

I can confirm that the internal energy of a substance is indeed dependent on its temperature. This is because the internal energy is a measure of the microscopic energy of the particles within the substance, and temperature is a measure of the average kinetic energy of those particles. Therefore, as the temperature of a substance changes, so does its internal energy.

Regarding the statement about an ideal gas and an isothermal process, it is partially true. In an ideal gas, the internal energy is solely dependent on the temperature and does not change during an isothermal process. However, this is only true for an ideal gas, which follows specific assumptions such as no intermolecular forces and negligible volume of the particles. In real gases, there may be a slight change in internal energy during an isothermal process due to deviations from these ideal conditions.

As for the change in internal energy during the condensation of a substance from saturated vapor to saturated liquid, it would depend on the specific substance and its properties. In an ideal scenario, the internal energy would remain constant as the temperature remains constant. However, in real substances, there may be a slight change in internal energy due to the release of latent heat during the phase change.

In conclusion, the statement about the internal energy of a substance being dependent on temperature is generally true, but there are certain factors that may affect this relationship, such as the properties of the substance and the ideal gas assumptions. It is important to consider these factors when studying the internal energy of a substance.