For Ideal Gases, the important assumptions are as below:
The intermolecular forces (Attractive Force or Repulsive Force) between the gas molecules are entirely negligible.
The volume occupied by the gas molecules themselves is entirely negligible relative to the volume of the container.
By the assumptions above, we can sure that there are no "Ideal Gas" in our real world.
However, scientists formulate the concept of Ideal Gases to make sure some gas law will always true. Or else, more errors will present in our calculations or data.
On the other hand, errors do exist when we dealt with Real Gases. We shall discuss this later.
If you are well with Ideal Gases, then here is the Ideal Gas Law:
is for Pressure, with the unit .
is for Volume, with the unit .
is the Number of moles, with the unit .
is a Constant, which is .
is for Temperature, with the unit .
Now, there is an example:
At a standard status (we mean by and ), what is the volume of a ?
First, we convert the units.
We now have all the details we wanted, by the formula we have
Thus, the volume is .