# Does 1 mole of all gas exert equal pressure

1. Jul 12, 2015

### rajeshmarndi

1 mole of all gas has equal number of molecules irrespective of their size. So I just wanted to know when 1 mole of molecules exerts pressure on the wall of a container, will it be same for all gases, irrespective of their molecules sizes.

2. Jul 12, 2015

### Avaron Cooper

When we consider them as ideal gases, it is when all the other factors like Volume and temperature are the same.
(pV = nRT)

3. Jul 13, 2015

### rajeshmarndi

Isn't it is the external atmospheric condition of the room where the experiment is carried.

Also like you say, when the ideal gas possess equal volume, temperature, pressure and number of molecules. Isn't the molecules whose sizes are bigger and when equal number of that molecules hit the wall of the container, per unit area, will result increase in pressure, than molecules smaller in size.

4. Jul 13, 2015

### Avaron Cooper

According to Avogardro's law, at the same temperature and pressure, equal volumes of different gases contain equal number of molecules. So if we apply this to pV= nRT, pressure also becomes equal.

5. Jul 13, 2015

### nasu

You forget that they are bigger but slower. The average speed is inverse proportional to the square root of molecular mass.
This will also have an effect on the number of molecules hitting the wall in a give time. It is less for more massive molecules.
All the effects compensate for ideal gas so that the pressure is independent of the molecular mass.

6. Jul 13, 2015

### rajeshmarndi

Thanks I understood it, now. There should be some factor which compensate the impacting of the bigger size molecules, which were equal in number as other sizes molecules, hitting equally in number the wall per unit area and producing the equal pressure.

7. Jul 13, 2015

### Staff: Mentor

If you're willing to sift through some sludge, it would be worth googling for "ideal gas law deviation".

$PV=nRT$ precisely describes the behavior of a hypothetical ideal gas. Real gases don't behave quite exactly the same way, although they come so close that we can generally use the ideal gas law and ignore the deviations (which are caused by the stuff that's being discussed above, and more). The google search I suggest will find much interesting discussion of these deviations.

8. Oct 12, 2016

### ronanoon

Van der waal equation for gases modifies the ideal gas law to account for both molecular size and intermolecular attraction. If you need high accuracy, read up on Beattie Bridgeman equation of state. I played with it in excel, and there are indeed quite interesting differences compared to the ideal gas law, especially at extreme pressures and/or temperatures.

9. Oct 12, 2016

### my2cts

For an ideal gas, where you can neglect particle-particle collisions and particle rotation the following holds.
Equal temperature means equal kinetic energy, so heavier molecules go slower. The number of collisions with the wall per unit time is proportional to v and the imparted momentum per collision is 2mv. Thus the imparted momentum to the wall per unit time, the force, is proportional to 2mv^2, that is proportional to the kinetic energy, that is to T. The exerted on the walls of the volume is therefore independent of the mass.