Safety boundary
Use supplied graphs and calculations only. No new reactive chemistry is required.
Explicit chemistry instruction
At constant temperature and pressure, Gibbs free energy combines enthalpy and entropy effects.
In the simplified criterion, ΔG<0 indicates thermodynamic favorability in the forward direction, ΔG>0 favors the reverse, and ΔG=0 corresponds to equilibrium.
This is a direction/equilibrium model, not a rate model.
Vocabulary: Gibbs free energy; ΔG; enthalpy; entropy; spontaneity.
Worked example
If ΔH=−40 kJ and TΔS=−10 kJ, then ΔG=−30 kJ and the forward direction is thermodynamically favored.
Guided question
If ΔH=+20 kJ and TΔS=+35 kJ, what is ΔG and what direction is favored?
Independent work
- Classify four ΔG signs.
- Calculate three ΔG values.
- State why ΔG does not predict speed.
Misconception check
Negative ΔG does not guarantee a fast reaction.
Formative check
What does ΔG=0 signify in this model?
Reveal response
Equilibrium under the stated conditions.
Mentor evidence conference
Ask Archaemenes to audit signs, units, thermodynamic conditions, and whether rate/direction are being kept distinct.
Teacher guidance
Foundation: Use sign tables.
Core: Calculate and interpret ΔG.
Extended: Connect ΔG with equilibrium and temperature.