Practice Test 2

A student compares two trials of the reaction between solid calcium carbonate and aqueous hydrochloric acid: $\text{CaCO}_3(s)+2\text{HCl}(aq)\rightarrow \text{CaCl}_2(aq)+\text{CO}_2(g)+\text{H}_2\text{O}(l)$. Trial 1 uses a single large marble chip; Trial 2 uses the same mass of calcium carbonate but crushed into a fine powder. The acid concentration, temperature, and total volume are the same, and the reaction mechanism is unchanged. Trial 2 produces $\text{CO}_2$ faster. Which statement best explains the difference in rate in terms of collisions?

Nitrogen dioxide gas reacts with carbon monoxide gas to form nitrogen monoxide and carbon dioxide. Two sealed reaction vessels have the same temperature and the same initial amounts of each gas, and the mechanism is assumed unchanged. Vessel 1 has a smaller volume than Vessel 2 (so the gases are at higher pressure in Vessel 1). The reaction proceeds faster in Vessel 1. Which statement best explains the faster rate in Vessel 1 using collision frequency or collision effectiveness?