“To calculate rate arithmetic
Of reaction, cite info kinetic.
(Common error displayed:
Writing capital K.
For rate constant, use lower-case metric!)”
The 24 July 2019 limerick examined a particular piece of symbolic notation that often sees some misapplication in General Chemistry.
“To calculate rate arithmetic /
Of reaction, cite info kinetic.”
Questions of whether a chemical reaction will occur or not involve “spontaneity,” a term with a specific meaning in chemistry. A reaction that is spontaneous is one that occurs naturally; “spontaneous,” as a descriptor in a chemical context, is unrelated to a reaction’s speed. (This is a case of unhelpfully mismatched chemical and everyday definitions.)
To communicate information about the rate of the reaction, we instead use kinetic data. The rate constant, or rate coefficient, is one piece of this data. It is represented by a lower-case k. The rate law of a given reaction indicates how the reaction rate depends on the rate constant and on the concentrations of species involved in the reaction. Determining a rate law from kinetic data is a common experimental goal.
“(Common error displayed: /
Writing capital K. /
For rate constant, use lower-case metric!)”
In chemistry, similar or identical symbols can be used in multiple settings with multiple meanings, a phenomenon that can be confusing. (For instance, the capital letter H, in chemistry, can represent hydrogen, or enthalpy, or the Hamiltonian operator: each with a distinct conceptual meaning.) As learners progress from novices to experts, they become adept at reading the context clues.
In General Chemistry coursework, students are typically introduced within the span of only a few weeks to two major topics: kinetics and equilibrium. In the former, the lower-case k represents a rate coefficient. In the latter, a capital K represents an equilibrium constant, a different quantity. While the two types of constants are related to one another, it is common to see them simply used interchangeably in introductory assignments: this is an “error displayed.”
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