# Why the kinetic energy is same as internal energy of ideal gas?

1. Jun 20, 2014

### Hardik Batra

Why the kinetic energy is same as internal energy of ideal gas?

2. Jun 20, 2014

### Matterwave

In an ideal gas (that we regularly study), there is assumed to be no interactions between the gas molecules. No interactions means no potential energy, so the only form of energy left is kinetic.

3. Jun 20, 2014

### Hardik Batra

Another question. Why are we use rms speed of gas molecules rather than average speed of gas molecules?

4. Jul 4, 2014

### Hardik Batra

for ideal gas P.E.=0
No interaction means no potential energy how?

5. Jul 4, 2014

### Staff: Mentor

Potential energy is defined in terms of an interaction force, specifically a conservative force.
$$V(P) = - \int_{P_0}^P {\vec F \cdot d \vec r}$$

6. Jul 5, 2014

### Hardik Batra

Potential energy for ideal gas is zero.
But what is the potential energy for real gas. how the potential energy of real is changing?
I don't get it from the equation? Could you explain by words?

7. Jul 5, 2014

### DrStupid

The internal energy of an ideal gas also includes the rest energy of the particles and the potential energy due to gravity but these energies are usually constant or negligible.

8. Jul 5, 2014

### Staff: Mentor

When two atoms or molecules come very close to each other, they exert small electrical forces on each other. Even though each atom or molecule has zero net charge, their charge distributions become distorted so that the net force between them becomes nonzero. For a simple example, two electric dipoles can exert forces on each other even though they each have zero net charge. This force is associated with a potential energy as per the equation above.

For more details, try searching for "van der Waals force" and "van der Waals potential".