Safety boundary
Use virtual calorimetry or teacher-supervised water-based calorimetry only. No unsupervised flames, reactive chemicals, or improvised heat sources.
Explicit chemistry instruction
Enthalpy change ΔH is a useful constant-pressure energy-accounting quantity.
Negative ΔH corresponds to exothermic reaction under the standard convention; positive ΔH corresponds to endothermic.
A reaction-energy diagram separates overall ΔH from activation-energy barriers.
Vocabulary: enthalpy; ΔH; reaction coordinate; activation energy; state function.
Worked example
If products lie 40 kJ/mol below reactants on an energy diagram, ΔH≈−40 kJ/mol.
Guided question
How can a reaction have negative ΔH but still require activation energy?
Independent work
- Interpret three reaction-energy diagrams.
- Calculate ΔH from relative energy levels.
- Distinguish ΔH from activation energy.
Misconception check
Exothermic does not mean barrier-free or instantaneous.
Formative check
What does ΔH compare?
Reveal response
The enthalpy of products with reactants.
Mentor evidence conference
Ask Archaemenes to audit signs, units, system boundaries, and whether the evidence supports the energy claim.
Teacher guidance
Foundation: Read energy diagrams.
Core: Connect calorimetry with reaction enthalpy.
Extended: Compare thermodynamic favorability with kinetic barriers.