# How was avagadros number was calculated

1. Sep 29, 2012

### SSJ2

i guess i have two questions....

1) the first is although I know the calculation of the number is based around the mass of 12 grams of carbon-12 and that there are 6.02*10^23 atoms here. How was it found that this many atoms of carbon was found in the 12 grams?

2) my second question is more based on his law which states "equal volumes of different gases at the same temperature and pressure contain the same number of particles."
referenced here

now my question here is that lets say we have a very small finite volume that can hold 10 hydrogen atoms, and assuming that the temperatures are equal and pressure is equal

how can the same volume hold the same number of atoms of radon which is much larger than hydrogen?

2. Sep 30, 2012

### Mute

I'll answer number 2 for you: that law is only valid as a statistical statement. That is to say that the law only holds on average. However, if you have a very large number of gas particles, the pressure and volume are always very very close to their average values, so you don't notice any deviations from the law. However, if you consider such a small number of atoms, statistical fluctuations will be large and you can much more easily see deviations from the "law".

3. Sep 30, 2012

### Staff: Mentor

In the gas, as long as the density is low enough, distance between atoms is so large their volume can be safely ignored.

Avogadro's constant is not something that can be calculated - it is something that has to be determined experimentally. Consult prof. Google.