When a solid substance is involved in a chemical reaction, only the matter at the surface of the solid is exposed to other reactants. If a solid has more surface area, more of it is exposed and able to react. Therefore, increasing the surface area of solid reactants increases the reaction rate. Look at the hammer and nails pictured in the Figure below . Both are made of iron and will rust when the iron combines with oxygen in the air. However, the nails have a greater surface area, so they will rust faster.
John and his neighbor both erected metal sheds in their yard John put his shed directly against his house so that only 3 sides were exposed to the elements. His neighbor Bob but his shed at the end of his yard leaving all four sides exposed.
Who's shed will rust the slowest?