Concept:In heterogeneous reactions involving a solid reacting with a liquid, the rate of reaction is heavily dependent on the total exposed surface area of the solid.
Formula:$$ \text{Rate} \propto \text{Surface Area of Solid Reactant} $$
Solution:- All options contain exactly 1 gram of Zinc, so the total mass is constant.
- A solid rod, pellet, or ribbon has a relatively small surface-to-volume ratio, meaning fewer Zinc atoms are exposed to the HCl molecules at any given moment.
- When Zinc is ground into a fine powder, it maximizes the surface area.
- This massive increase in exposed atoms drastically increases the collision frequency between Zn and HCl, massively increasing the rate of hydrogen gas formation.
Why other options are incorrect:Rods, pallets, and ribbons all have significantly less exposed surface area compared to finely divided powder, leading to slower reactions.
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