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.
piece - an instance of some kind; it was a nice piece of work; he had a bit of good luck bit case, instance, example - an occurrence of something; it was a case of bad judgment; another instance occurred yesterday; but there is always the famous example of the Smiths