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.
A tiny or a very small piece (of something). (biology or biochemistry) An extremely small particle or substance, especially at cellular or structural level, as a biomolecule. (physics and chemistry) The smallest unit of an element or compound, made up of two or more atoms held together by strong chemical bond.