Energy profiles, activation energy and catalyst claims
≈ 48 minEnergy profiles, activation energy and catalyst claims
An energy profile has reactants, products and a peak representing the activated state. The vertical difference from reactants to the peak is activation energy, Eₐ. The vertical difference from reactants to products is ΔH. A catalyst provides an alternative pathway with a lower activation energy; it increases the rate but does not change the energy levels of reactants and products, so it does not change ΔH. Read diagrams carefully: the height of a drawn peak is relative to the labelled energy axis, and a reaction profile does not show time on the horizontal axis.
Work it through
If reactants are at 50 kJ mol⁻¹ and the peak is at 125 kJ mol⁻¹, Eₐ is 75 kJ mol⁻¹. A catalyst may lower the peak, for example to 95 kJ mol⁻¹, but if products stay at the same energy, ΔH is unchanged. The catalyst changes the pathway, not the energy difference between initial and final states.
Mastery target
Extract activation energy and ΔH from a reaction profile and explain accurately what a catalyst changes and does not change.
What does a catalyst change on an energy profile?
Name the key chemistry term from Energy profiles, activation energy and catalyst claims that best fits the explanation and visual model.
Reactants are at 50 kJ mol⁻¹ and the peak is at 125 kJ mol⁻¹. What is the activation energy in kJ mol⁻¹?
Which statement corrects a common misunderstanding in Energy profiles, activation energy and catalyst claims?