Final answer:
The powdered zinc will react the fastest with dilute hydrochloric acid as it has the largest surface area, which leads to a more rapid reaction and quicker production of hydrogen gas.
Step-by-step explanation:
At STP, which 4.0-gram zinc sample will react fastest with dilute hydrochloric acid? The powdered zinc (option 3) will react the fastest. This is because when zinc is in powdered form, it has the highest surface area, which allows more acid particles to come into contact with the zinc particles at once, leading to a faster reaction rate.
When a solid reacts with a liquid to produce a gas and a solution, as in the reaction of solid zinc metal with aqueous hydrochloric acid, the surface area of the solid has a significant impact on the reaction rate. The reaction produces zinc chloride (ZnCl₂) and hydrogen gas (H₂) according to the balanced equation: Zn(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂(g).
The larger the surface area, the more readily the hydrochloric acid molecules can collide with the metal, leading to faster production of hydrogen gas. This is exemplified by powdered zinc reacting more rapidly than other forms such as a lump, bar, or sheet metal of the same mass.