Surface Area

How does surface area affect the rate of a reaction? Did you try the Alka-Seltzer experiment? If you did, you know that crushing a tablet up into tiny little pieces greatly speeds up the reaction. Why is this? It all has to do with surface area. The more surfaces exposed for reaction, the faster the reaction proceeds. Think of it this way. If you were trying to catch a mouse in your basement, would you rather have ten people, lined up single file, walk straight up to the mouse, one after the other? Or, instead, would you rather form a circle around the mouse with those ten people? You probably would say form a circle. Why is this more effective? By surrounding the mouse, you are covering more areas where the mouse can escape. If you approach the mouse from only one direction, it can escape in many other directions. The same principle governs dissolving tablets. When you crush a tablet, you expose new surfaces that were originally on the inside of the tablet. These surfaces can react with water. With a greater number of surfaces, the water is able to surround more and more of the tiny pieces of the tablet, dissolving it faster.

Does this make sense? Let's explain it another way. Say I have a whole tablet. You could probably wander through mathematical equations and eventually be able to tell me, in inches, how much of the surface area is exposed to reaction on that tablet. If you break that tablet in half, you don't have more tablet than when you started, but you do have something more. You have one more surface on each half of the tablet to react with. Do you see why? The tablet was broken in half, and the slice down the middle now is exposed to reaction. So, more of the tablet is exposed for reaction, so the surface area has increased. The higher the surface area, the faster the reaction proceeds.

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