Measure activation energy from the reactants
- The idea
- Predict
- See it
- Why
- Check
The idea
“Activation energy is how high the peak sits on the energy diagram.”
The peak is the first thing your eye goes to, so reading its height feels natural. The reactants start partway up the graph.
The short version
The mistake: Activation energy is how high the peak sits on the energy diagram.
What's actually true: Activation energy is the rise from the reactants' energy up to the top of the peak.
- Activation energy, Ea, is the energy the reactants must gain to reach the transition state, the unstable arrangement at the top of the peak.
- So Ea is a difference. Subtract the reactants' energy from the peak's. Starting from the products gives the reverse reaction's Ea.
- An enzyme lowers the peak but leaves the reactants and products where they were. How far the peak drops is how much Ea fell. The climb that remains is the new Ea.
On the exam: Ea starts at the reactants. Subtract their energy from the top of the peak.