Mole.

So propose a coin has a thickness of 2.3mm, what would the height (in km) of a stack containing one mole of these coins?

Hmmmm, can you use number of particles = number of moles x Avagadro's constant, so that 1 x 6.02x10^23 to get the number of coins. Then multiply be 2.3 to get the height. To convert to km just minus 5 from the resulting number?

>>To convert to km just minus 5 from the resulting number?

wat

>>wat
Sorry I meant the resulting power, as in you end up with 1.3846E24mm, to convert to km make it 1.3846E19km.

I think it's minus power 6, a 1mm=10^-3m = 10^-3 * 10^-3 km
so that would make it 1.3846*10^18kms