Safety boundary
Use virtual calorimetry or teacher-supervised water-based calorimetry only. No unsupervised flames, reactive chemicals, or improvised heat sources.
Explicit chemistry instruction
Thermochemistry tracks energy transfer between a defined system and its surroundings.
When the system absorbs heat, q_system is positive; when the system releases heat, q_system is negative under the usual chemistry sign convention.
A temperature change in the surroundings can provide evidence about the system’s energy change, but only after the boundary and assumptions are stated.
Vocabulary: system; surroundings; heat; exothermic; endothermic.
Worked example
A reaction warms surrounding water. The water gains heat, so the reacting system released energy to the surroundings.
Guided question
Why can the sign of q differ for the system and surroundings?
Independent work
- Classify four scenarios as exothermic or endothermic.
- Draw an energy-flow diagram for one reaction.
- State the chosen system boundary.
Misconception check
Temperature and heat are not the same quantity; temperature is an intensive measure while heat is energy transferred.
Formative check
What sign does q_system have for an endothermic process?
Reveal response
Positive.
Mentor evidence conference
Ask Archaemenes to audit signs, units, system boundaries, and whether the evidence supports the energy claim.
Teacher guidance
Foundation: Use energy-flow arrows.
Core: Explain sign convention and system boundary.
Extended: Analyze how redefining the system changes bookkeeping.