Suppose it's x number of moles. You take a second eraser identical to this one, stack it on top of this one, and what will you get? You will get an eraser with x number of moles. A second eraser with x number of moles. The result is two x number of moles. So increasing this size or this system to twice its size increases the number of moles to twice number of original moles, number of moles increases.