Why should the solid be crushed before reacting?

• A. It increases the surface area for a faster rate of reaction.
• B. It changes the chemical composition.
• C. It makes the solid heavier.
• D. It reduces solubility.

Answer: (A)

The concept being tested is how surface area affects the rate of a reaction. Crushing the solid breaks it into many smaller pieces, which increases the total surface area exposed to the reacting substance. With more surface area, there are more particles of the solid in contact with the other reactant at any moment, so collisions between reacting particles occur more frequently. According to collision theory, more frequent effective collisions speed up the reaction. Crushing does not change what the solid is made of, and it does not add mass or make it heavier. It also does not reduce solubility; it may even help dissolve faster because more surface is exposed, but the underlying solubility value isn’t decreased.