# Increased specific surface area

Nano-objects are extremely small: between 1 and 100 nm according to common definitions.

The surface-to-volume ratio of substances changes with the size. Compared to microcrystalline and macrocrystalline materials, materials at the nanometer scale have a much larger surface area per volume. A larger surface generally means that nanoparticles are more reactive as reactions mostly take place on the surface. The larger the surface, the faster are the chemical reactions.

The high increase of nanoparticles’ surface can be illustrated by a simple arithmetic example: consider a cube with an edge length of 1 m. The surface of this cube is 6 m^{2}. The volume is 1 m^{3}. If this cube is divided into smaller cubes with an edge length of 10 cm, 1000 smaller cubes are formed. Together, 1000 small cubes have a surface area of 60 m^{2} - that is a tenfold surface increase at the same weight. Repeat the process several times until the cubes have an edge length of 100 nanometers (10 million divisions), the surface area of all these nanoparticles together would be 60 km^{2}. This corresponds to the area of 8000 football fields!