How Does the Ideal Gas Theory Account for Volume and Mass?

[wanderlust44]

This might be a stupid question, but I am confused about the ideal gas theory. I know that we assume high temperatures and low pressures, and that the volume is negligible when we compare it to a container, but my textbook is very confusing about this point.

It says assume zero/negligible volume and mass, but then goes on to calculate 1 mol of any gas at STP is 22.4L. Also, it says that the conditions of ideal gas do assume that there is no volume or IMF, but that it would have some mass. How can it have no volume and a 22.4L volume (and no mass)? I think I need clarification with regards to what it is talking about. Is it talking about the particles?

Also, if we look at the graph of pressure and temperature, wouldn't negligible volume mean 0K rather than 273.15K? Thanks for the clarification.

 

[lisab]

Could the text be saying, assume zero/negligible *change* in mass and volume?

 

[SteamKing]

It would be better for us to provide direct quotes from your text on this point. All we are doing now is playing a game of Telephone.

 

[Yanick]

No volume refers to the volume taken up by a specific atom of gas, not the bulk gas as a whole. The 22.4L of 1mol at 1bar pressure is only an approximation and does not hold for real gases, in reality the small/light monatomic gases are close to 22.4L but not exactly there. The discrepancy lies in the fact that each particle of gas does in fact take up some volume and that there are slight intermolecular forces.

 

[LudusRex]

It is not a stupid question at all! The ideal gas theory can be confusing, so let's break it down.

Firstly, the ideal gas theory is a simplified model that helps us understand the behavior of gases at high temperatures and low pressures. It is not a perfect representation of real gases, but it is a good approximation in many situations.

Now, let's address the issue of volume and mass. When we say that an ideal gas has zero or negligible volume, we are referring to the volume of the particles themselves. In other words, we are assuming that the particles of the gas have no size and can be squeezed into any container without taking up any space. This is obviously not true for real gases, but it helps us simplify the calculations and understand the underlying principles.

On the other hand, when we talk about the volume of a gas at STP (standard temperature and pressure), we are referring to the volume of the container that the gas is in. This is why we say that 1 mol of any gas at STP has a volume of 22.4L. This is the volume of the container, not the volume of the gas particles themselves.

Now, let's talk about mass. The ideal gas theory does assume that particles of an ideal gas have mass, but it is not a significant factor in the calculations. This is because the particles are assumed to have no volume, so their mass does not contribute to the overall volume of the gas.

Finally, regarding the graph of pressure and temperature, it is true that at 0K, the volume of an ideal gas would be 0. However, we typically use 273.15K (or 0°C) as the starting point on the graph because it is a more practical and commonly used temperature scale. The concept of negligible volume still holds at this temperature, as the volume of the particles is still assumed to be negligible.

I hope this helps clarify the concepts of ideal gases and kinetics for you. Remember, the ideal gas theory is just a simplified model and may not always accurately represent real gases. But it can still be a useful tool for understanding the behavior of gases.