Measuring instantaneous rates is the most direct way of determining the rate law of a reaction, but it is not always convenient, and it may not be possible to do so with precision.
piece (pÄs) n. 1. A thing considered as a unit or an element of a larger thing, quantity, or class; a portion: a piece of string. 2. A portion or part that has been separated from a whole: a piece of pie. 3. An object that is one member of a group or class: a piece of furniture.
pile - (often followed by `of') a large number or amount or extent; a batch of letters; a deal of trouble; a lot of money; he made a mint on the stock market; see the rest of the winners in our huge passel of photos; it must have cost plenty; a slew of journalists; a wad of money.