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.
(loin) n. 1. The part of the body of a human or quadruped on either side of the backbone and between the ribs and hips. 2. One of several cuts of meat, such as tenderloin, taken from this part of an animal's body, typically including the vertebrae of the segment from which it is taken. 3. loins.