Zinc metal reacts with 0.1 M hydrochloric acid to form hydrogen gas and zinc chloride solution - VCE - SSCE Chemistry - Question 3 - 2006 - Paper 1

When zinc is powdered, its surface area increases significantly. A larger surface area allows more frequent collisions between the zinc particles and hydrogen ions from the hydrochloric acid. The frequency of these successful collisions is critical in increasing the rate of reaction, as more interactions mean that more hydrogen gas can be produced in a shorter time. Thus, it is this higher frequency of collisions that leads to a more vigorous production of hydrogen gas in powdered zinc compared to zinc in large pieces.