A student is measuring the effect that surface area has on the rate of chemical weathering. He dissolves several 5-gram samples of calcite in an acid. The samples range from a simple rock, to several smaller pieces, to a fine powder. He observes that the 5 grams of powder dissolve the fastest, and the single 5-gram rock dissolves the slowest? Based on this information, how might mechanical weathering affect the rate of chemical weathering?