“A chemist considers attentively
That a property’s named as ‘intensive’; sees
How the attribute meant
Relies NOT on extent.
(Definition denotes independency.)”
The 4 April 2020 limerick addressed a determination that is often seen in early chapters of introductory chemistry textbooks: classifying whether a property of a given sample is intensive or extensive. Describing matter precisely is a consistent goal in General Chemistry coursework, and this is one important type of such descriptions.
“A chemist considers attentively /
That a property’s named as ‘intensive’…”
The extensive/intensive classification of properties is deceptively simple; I often notice in grading that such questions have been more challenging than I intended. To analyze these topics, it’s thus helpful to “consider attentively.” In this poem’s hypothetical scenario, a chemist will be deciding whether or not a given property is intensive.
“…Sees/ How the attribute meant /
Relies NOT on extent. /
(Definition denotes independency.)”
Intensive properties, which do not vary with the amount of a substance, are often most easily classified in opposition to extensive properties, which do vary with the amount of a substance.
For a specific example, we can imagine we have a sample of ten grams of water at room temperature, then further imagine that we divide that sample in half. Each half of the original sample contains five grams of water; each half of the original sample is at room temperature. Mass, then, is an extensive property: each half-sample has one-half the mass of the total sample. Temperature is an intensive property: it is the same for the total sample and each half-sample.
The mnemonics I share with students are two-fold. First, I remind them that an extensive property relies on the “extent” of the sample; second, I note that an intensive property is independent of the amount of the sample, noting the similar prefixes.
In this poem, after the chemist has “considered attentively,” they correctly conclude that the property is indeed intensive. Here, “the attribute meant / [r]elies NOT on extent”: the property described is independent of amount. Further, they remember that the definition of an intensive property “denotes independency.”
Chemphasis 