What is ideal gas? Under what conditions can real gas be treated by ideal gas model?

What is ideal gas? Under what conditions can real gas be treated by ideal gas model?

The gas that strictly obeys the equation of state (PV = (M / M) rt = NRT) is called ideal gas. From the microscopic point of view, it refers to the gas whose volume of the molecule itself and the force between the molecules are negligible, which is called ideal gas
The ideal gas should be such a gas:
1. The molecular volume is negligible compared with the gas volume;
2. There is no mutual attraction between molecules;
3. The collision between molecules and between molecules and the wall does not cause kinetic energy loss
4. In the container, the velocity exchange occurs when the gas molecules collide without kinetic energy loss
5. When solving thermal problems, we simply think that the molecular potential energy is zero and the molecular kinetic energy is not zero
6. The internal energy of ideal gas is the sum of molecular kinetic energy
In real gases, the properties of gases which are not easy to liquefy themselves are very similar to ideal gases, among which hydrogen and helium are the closest to ideal gases. Generally, the properties of gases are also very close to ideal gases when the pressure is not too high and the temperature is not too low. Therefore, real gases are often treated as ideal gases, In particular, the calculation can be greatly simplified
When the gas is at high pressure or low temperature, their state changes will deviate from the gas state equation significantly, and the equation needs to be modified according to the actual situation

What is the method of controlling some factors to keep them unchanged and then finding out the relationship between other factors?

It's very simple. It's called control variable method