# Energy of Ideal Gas: Internal E & Kinetic E

• B
• Bhope69199
In summary: The model also breaks down at high pressures and low temperatures, I imagine most physicists would be aware of this or at least suspect it.
Bhope69199
Hi,

When calculating the energy of an ideal gas we neglect the potential energy and calculate the kinetic energy using:

K.E = 3 /2 n R T

My question is why do we not consider the electrostatic energy of the gas?

If I am trying to work out the internal energy of 1 mol of Radon, why do I only require the kinetic energy and not the energy that was required to bring the electrons and protons together? Is this energy not held within the gas?

That's the meaning of ideal gas, a gas whose particles don't interact with each other. Its an approximation! Of course you can consider interactions and have a more precise model, but that means you should do harder calculations.

If your gas is so hot that electrons can be removed from atoms (=your gas is actual a plasma), you cannot approximate it as ideal gas any more.

Bhope69199 said:
Hi,

When calculating the energy of an ideal gas we neglect the potential energy and calculate the kinetic energy using:

K.E = 3 /2 n R T

My question is why do we not consider the electrostatic energy of the gas?

If I am trying to work out the internal energy of 1 mol of Radon, why do I only require the kinetic energy and not the energy that was required to bring the electrons and protons together? Is this energy not held within the gas?
When snooker balls collide it is not necessary to consider the "electrostatic energy" of the snooker balls..molecules are considered to be 'snooker balls' in the simple kinetic theory of gases

Bhope69199 said:
Hi,

When calculating the energy of an ideal gas we neglect the potential energy and calculate the kinetic energy using:

K.E = 3 /2 n R T
Be aware that this formula is only valid for a monatomic ideal gas. It is not valid if the gas molecules have 2 or more atoms -- e.g. O2, N2, CO2, etc.

I've personally known physics teachers who were unaware of this.

vanhees71
Redbelly98 said:
Be aware that this formula is only valid for a monatomic ideal gas. It is not valid if the gas molecules have 2 or more atoms -- e.g. O2, N2, CO2, etc.

I've personally known physics teachers who were unaware of this.

oops...should perhaps have qualified 'translational kinetic energy'
this is more or less implied among physicists when the model is based on snooker balls, as far as I know there are no diatomic snooker balls.
Such a simple model has many limitations but is surprisingly informative.
The model also breaks down at high pressures and low temperatures, I imagine most physics teachers would be aware of this or at least suspect it.

## 1. What is the internal energy of an ideal gas?

The internal energy of an ideal gas is the total energy of all the molecules in the gas, including their kinetic energy and potential energy.

## 2. How is the internal energy of an ideal gas related to its temperature?

The internal energy of an ideal gas is directly proportional to its temperature. This means that as the temperature of the gas increases, so does its internal energy.

## 3. What is kinetic energy in the context of an ideal gas?

Kinetic energy in an ideal gas refers to the energy that the gas molecules possess due to their motion. It is a type of mechanical energy and is related to the speed and mass of the molecules.

## 4. How does the kinetic energy of an ideal gas relate to its pressure?

The kinetic energy of an ideal gas is directly proportional to its pressure. This means that as the pressure of the gas increases, so does its kinetic energy.

## 5. Can the internal energy of an ideal gas change?

Yes, the internal energy of an ideal gas can change. It can change due to changes in temperature, pressure, or volume. It can also change when the gas undergoes a physical or chemical change.

• Classical Physics
Replies
18
Views
1K
• Classical Physics
Replies
15
Views
2K
• Classical Physics
Replies
14
Views
1K
• Classical Physics
Replies
5
Views
5K
• Introductory Physics Homework Help
Replies
4
Views
2K
• Classical Physics
Replies
4
Views
2K
• Classical Physics
Replies
6
Views
361
• Introductory Physics Homework Help
Replies
5
Views
181
• Classical Physics
Replies
2
Views
1K
• Classical Physics
Replies
2
Views
1K