# Throttling Ideal Gas: Is Temperature Change Involved?

• starryskiesx
In summary, the conversation discusses the concept of throttling in relation to an ideal gas. It is mentioned that when forcing the gas through a capillary into a vacuum, there will be no temperature change. However, this thought experiment may not be practical in reality due to various factors such as work, internal heat, and external pressure. Therefore, caution should be exercised when applying this concept in experiments.
starryskiesx

I've read that for an ideal gas, if you force it through a capillary into a vacuum and allow it to equilibrate, it will experience no temperature change. I was wondering if this is correct, and if anything changes when you're forcing it through with a piston for example.

Even with an ideal gas, this sort of thought experiment is very misleading and about impossible to make in practice...

First, the gas would take the temperature of the capillary.

Then, the gas that at some time remains in the bottle pushes the gas that goes out, gives a work, and loses internal heat. It cools down, while the flowing gas receives some work that it may transform into internal heat, depending on the experiment, or into kinetic energy, or into work against the external pressure.

It's only after a very long time that the gas may regain some form of equilibrium - between the part flown first out and the part flown last - that the temperature is uniform, and then, with a ideal gas, you may observe the same temperature as before the expansion.

So it's much more a question of setup and time than of the gas being ideal. In two words: be careful.

## 1. What is throttling of an ideal gas?

Throttling of an ideal gas refers to the process of allowing the gas to expand rapidly through a small opening, which results in a decrease in pressure and temperature.

## 2. How does throttling affect the temperature of an ideal gas?

Throttling causes a decrease in temperature of an ideal gas due to the rapid expansion of the gas. This is known as the Joule-Thomson effect.

## 3. Is a temperature change involved in throttling an ideal gas?

Yes, a temperature change is involved in throttling an ideal gas. As the gas expands, the temperature decreases due to the decrease in pressure.

## 4. Why does the temperature decrease during throttling of an ideal gas?

The temperature decreases during throttling of an ideal gas due to the conversion of internal energy to kinetic energy as the gas expands. This results in a decrease in the average kinetic energy and therefore, a decrease in temperature.

## 5. How is the Joule-Thomson coefficient related to throttling of an ideal gas?

The Joule-Thomson coefficient is a measure of the change in temperature during throttling of an ideal gas. It is equal to the slope of the temperature-pressure curve and can be used to determine if the temperature will increase or decrease during throttling.

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