(simple?) question on number of molecules in an area

[rwooduk]

Homework Statement

Homework Equations

Please see below.

The Attempt at a Solution

I'm probably being really stupid here but how can the number of molecules equal

If we integrate we get a volume multiplied by density, how can that equal a number of particles?

 

[BvU]

$\rho$ is not a mass density (kg/m³) but a particle density (number of particles/m³).

 

[rwooduk]

$\rho$ is not a mass density (kg/m³) but a particle density (number of particles/m³).

Of course! many thanks for clearing this up.