# Why does 1 amu = 1 g/mol?

Mar 26, 2018

Due to the definitions...

#### Explanation:

The mole is defined as the number of particles in $12 \setminus \text{g}$ of carbon-$12$, known as ""^12C. So, we say that in one mole of carbon-$12$, the sample has a mass of $12 \setminus \text{g}$.

In other words,

$\text{mass of carbon-12"=12 \ "g/mol}$.

Still with me? Good.

Now, we also know that the mass of a single carbon-$12$ atom is exactly $12 \setminus \text{amu}$, as it is an isotope.

And so,

$\text{mass of carbon-12"=12 \ "amu/atom}$

Combining, we have:

$12 \setminus \text{amu/atom"=12 \ "g/mol}$

$\implies 1 \setminus \text{amu/atom"=1 \ "g/mol}$

Therefore we just proved that an atomic mass unit is the same thing as grams per mole. Hope this helps!

For a further explanation, visit:

https://chemistry.stackexchange.com/questions/13764/amu-and-g-mol-relation