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# Counting Calories (or Joules)

Procedures in bomb calorimetry
Take place in a setting of constant V.
From the temperature change
In solution, arrange
Calculations for internal energy.

The 27 January 2020 limerick describes the main mathematical aims of a chemistry lab technique called bomb calorimetry. The language is, unsurprisingly, less precise than I’d teach in class, but the poem provides an overview of the experiment!

“Procedures in bomb calorimetry /
Take place in a setting of constant V.”
Calorimetry experiments measure the transfer of heat energy; different types of calorimetry involve different types of experimental settings and instruments.  Constant-pressure calorimetry was generally described in a previous entry: if a lab vessel is open to the air, the pertinent chemical reaction occurs at constant (atmospheric) pressure; coffee-cup calorimetry is one common example.

By contrast, this poem highlights constant-volume (“constant V”) calorimetry, or bomb calorimetry, in which a reaction occurs in a sealed metal container. A chemical sample is placed in this container (the “bomb”), which is then filled with oxygen; ignition of the sample via operation of the calorimeter causes a combustion reaction to occur.

“From the temperature change /
In solution, arrange /
Calculations for internal energy.”
The ending lines sum up many calorimetry calculations: information about a reaction is inferred from a measurement of the temperature change in the surrounding water.

In constant-volume calorimetry, the oxygen bomb is placed in a water bath in the larger calorimeter.  The “in solution” phrase is linked to constant-pressure calorimetry more directly, but the theme of measuring the temperature change in the water is consistent.  For an exothermic reaction, for instance, the temperature of the surrounding water will rise, because the reaction (the system) releases heat energy to its surroundings.

Depending on the experimental constraints, calculations involving this heat energy transfer then give information about the enthalpy change of the process (𝛥H, or “Delta H,” in constant-pressure calorimetry) or the internal energy change of the process (𝛥U, or “Delta U,” in constant-volume calorimetry, as described here).  Such quantities are typically reported in calories (cal) or joules (J); hence this piece’s title.