A plot of energy against reaction progress highlighting the barrier and enthalpy change.
Practise Thermodynamics & Energetics All Thermodynamics & Energetics topics
An energy profile plots the potential energy of a reacting system against the reaction coordinate, which tracks progress from reactants to products. The highest point on the curve, the transition state, lies above the reactants by the activation energy, which is the barrier that must be overcome for reaction to occur. The vertical difference between the reactant and product levels gives the enthalpy change, which is independent of the barrier. A catalyst lowers the barrier by providing an alternative pathway but does not alter the reactant or product energies or delta H. This profile is the standard way to depict kinetics and thermodynamics together.
Key ideas: The reaction coordinate runs from reactants through the transition state to products. The forward barrier is Ea, and the reverse barrier is Ea minus delta H. A catalyst lowers both barriers equally and leaves delta H unchanged. Intermediates appear as valleys between peaks.
Common mistakes and connections: Do not mistake the peak for an intermediate, because the transition state cannot be isolated. Another error is to say that a catalyst makes a reaction more exothermic. The diagram unites thermodynamics, shown by delta H, with kinetics, shown by barrier height.
Reactants must climb over the activation barrier (75 kJ/mol) to reach products; delta H is the net difference between starting and final levels. The interactive lesson shows this as a live animation or chart.
An enzyme that lowers the activation energy of a reaction speeds it up greatly while leaving the overall enthalpy change unchanged.
A plot of energy against reaction progress highlighting the barrier and enthalpy change.
Activation Energy Profile is a intermediate topic in Thermodynamics & Energetics. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Thermodynamics & Energetics first: Biofuels, Hess's Law Cycle Diagram, Enthalpy Level Diagram.
The next topics in Thermodynamics & Energetics are Entropy of Mixing and Entropy and the Arrow of Time.
Yes. The interactive lesson includes a self-check question on Activation Energy Profile, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Activation Energy Profile is topic 77 of 91 in Thermodynamics & Energetics.