In a heterogeneous system such as wood burning in oxygen, the surface area of the solid can be a factor in the rate of the reaction. Increased surface area of the wood means more collisions with oxygen molecules. To understand how surface area increases when dividing a solid, do the following:

(a) Draw a cube that is 2 cm on a side. What is its total surface area?

(b) Divide each face of the cube into four equal sections. If you were able to take the cube apart on the lines you have just drawn, how many cubes would you have?

(c) What are the dimensions of the new cubes?

(d) What is the total surface area of all the new cubes What will happen if you divide the cubes again?

(e) Now consider burning a log or burning all the toothpicks that could be made from the log. What effect would surface area have on the rate that each burns? Would you rather try to start a campfire with a log or with toothpicks?