Unit 05 · Thermochemistry & Energy
Every reaction is also an energy transaction. This unit covers enthalpy and the sign conventions that mark a reaction exothermic or endothermic, calorimetry as the measurement of heat flow, Hess's law for adding reactions to reach an unmeasurable one, and bond energies as the accounting of energy stored in chemical bonds. Mastery means you can predict, measure, and reconcile the heat released or absorbed by a real reaction.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Enthalpy & energy diagrams | Confuses exothermic and endothermic or their signs. | Labels ΔH signs but misreads energy diagrams. | Interprets energy diagrams and assigns ΔH signs, relating them to bond making and breaking. |
| Calorimetry calculations | Cannot set up q = mcΔT. | Uses the equation but mishandles units or the system–surroundings sign. | Calculates heat transfer correctly and assigns it to the reaction with the right sign. |
| Hess's law | Adds reactions without adjusting their enthalpies. | Manipulates equations but forgets to flip or scale ΔH. | Combines, reverses, and scales reactions to find an overall ΔH consistently. |
| Bond energy estimates | Ignores bonds when reasoning about energy. | Sums bond energies but mixes up bonds broken vs. formed. | Estimates ΔH from bond energies, correctly subtracting bonds formed from bonds broken. |
| Lab technique (calorimetry) | Loses heat to the surroundings and ignores it. | Runs the calorimeter but records temperature carelessly. | Measures ΔT precisely, accounts for heat loss, and computes a defensible ΔH. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“The reaction warmed the water, so heat left the system — it’s exothermic and ΔH is negative. I used q = mcΔT on the water for the heat, then divided by the moles of fuel to report it per mole.”
“It got hot, so energy went in. Enthalpy is just the heat. I’d add the numbers from the table together.”
You demonstrate this unit by running a coffee-cup calorimetry experiment, predicting the enthalpy change and reconciling it with your measured temperature data aloud — not a multiple-choice test. A criterion counts as mastered only when your measured heat matches your calculation within reason and you can explain the discrepancy. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.