To illustrate principles of thermochemistry, we devote one laboratory session for making thermochemical measurements and doing demonstrations with simple chemicals and devices that involve temperature changes. Using calorimeters made of styrofoam cups, students determine heat of neutralization (kJ/mol) between HCl (aq) and NaOH (aq) using 1.0 M versus 2.0 M stock solutions. These acid-base measurements illustrate Hess’s Law and its quantitative aspects. Students also determine temperature changes that occur by dissolving a designated mass of ionic solids in 50.0 g H2O and then calculating qreaction per mol of salt. Students must determine if their observed temperature change (△T=Tfinal –Tinitial) correlates qualitatively with an exothermic or endothermic reaction. A typical quantitative ranking for △Hsolution (J/mol) from the most exothermic to most endothermic is: CaCl2, KOH, NaOH, NaCl, KCl, NH4Cl, sodium acetate trihydrate, and NH4NO3. Recently we have expanded the list of solutes to include some readily available household chemicals, thus making this experiment adaptable and safe for low budget high school labs as well as remote laboratory exercises. Both in the laboratory and in the lecture setting, we also perform demonstrations with inexpensive, commercially available devices to demonstrate thermochemical principles such as: cooling packs with NH4NO3; hot packs involving the oxidation of iron filings; glove warmers with sodium acetate; FRH (flameless rations heaters) and MRE (meals-ready-to-eat) with oxidation of magnesium; thermochromic inks and pigments to detect temperature changes. Materials of different heat capacities are used to show the impact of heat conductivity on heat transfer, whereas enthalpy of evaporation is easily shown with isopropyl alcohol. Combining traditional laboratory experiments with these demonstrations of everyday applications provides a good foundation for our General Chemistry I students to understand the definition and role of heat transfer in thermochemistry. These chemistry exercises now stand at the crossroads, providing options for in-person and remote learning.

Teaching thermochemistry at the crossroads using experiments and demonstrations

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