How do you find the activation energy from an energy diagram?

The activation energy Ea is the vertical distance from the reactant energy level up to the top of the transition-state peak. In this tool, the peak energy equals the reactant energy plus Ea, and the Ea arrow is drawn from the reactant level straight up to the peak. A taller peak means a larger activation energy and a slower reaction.

How can you tell if a reaction is exothermic or endothermic?

Compare the product level with the reactant level. If the products are lower than the reactants the reaction is exothermic and ΔH is negative (energy is released). If the products are higher than the reactants it is endothermic and ΔH is positive (energy is absorbed). The tool detects this automatically from the energies you enter and points the ΔH arrow down for exothermic reactions and up for endothermic ones.

What does a catalyst do to a reaction coordinate diagram?

A catalyst lowers the activation energy by offering an alternative pathway, so the transition-state peak is lower. The reactant and product energies are unchanged, which means ΔH stays the same. Turn on "Show catalyzed pathway" to draw a second, dashed curve with a smaller Ea so you can compare the catalyzed and uncatalyzed barriers.

What is the difference between a transition state and an intermediate?

A transition state is the highest-energy point on the curve — a maximum where bonds are partly broken and partly formed — and it cannot be isolated. An intermediate is a local minimum that appears between two transition states in a multi-step reaction; it is a real, if short-lived, species that forms in one step and is used up in the next. Use the two-step option to show both on the same diagram.

Can I download or print the reaction coordinate diagram?

Yes. The precise mode exports a clean SVG or a high-resolution PNG (rendered at 2x) that drops neatly into worksheets, lab reports, and slides. Precise mode runs entirely in your browser and does not use image-generation credits.

Chemistry Tool

Reaction Coordinate Diagram Generator for Energy Profiles

Q: What is a reaction coordinate diagram?

A reaction coordinate diagram, also called an energy profile or potential energy diagram, plots the potential energy of a reacting system (y-axis) against the reaction progress (x-axis, reactants on the left, products on the right). It shows the reactant and product energy levels, the transition-state peak, the activation energy needed to start the reaction, and the overall enthalpy change ΔH.

Draw a labeled reaction coordinate diagram — transition-state peak, Ea and ΔH arrows, exothermic/endothermic auto-detect, and catalyzed pathways.

Auto exothermic vs endothermic (ΔH)Labeled activation energy & transition stateCatalyzed pathway & two-step intermediateSVG & PNG export

Energy levels (kJ/mol)

Reactant energyProduct energyActivation energy (Ea)

Show catalyzed pathwayTwo-step (with intermediate)

Readout

Type: Exothermic
ΔH: -60 kJ/mol (released)
Activation energy: 80 kJ/mol
Peak energy: 180 kJ/mol

Reaction Coordinate Diagram Examples

Common energy profiles: exothermic, endothermic, catalyzed, and multi-step reactions

View:

Labeled Reaction Coordinate Diagram

An energy profile with reactants, transition state, products, Ea and ΔH all labeled.

labeledenergy profile

Exothermic Energy Profile

An exothermic profile: products below reactants, energy released, ΔH negative.

exothermic

Endothermic Energy Profile

An endothermic profile: products above reactants, energy absorbed, ΔH positive.

endothermic

Activation Energy Diagram

A diagram emphasizing Ea as the climb from the reactant level to the transition state.

activation energytransition state

Catalyzed vs Uncatalyzed

Two pathways compared: the catalyzed route has a lower activation energy peak.

catalyst

Two-Step Reaction with Intermediate

A multi-step profile with two transition states and a stable intermediate between them.

multi-stepintermediate

What is a reaction coordinate diagram?

A reaction coordinate diagram — also called an energy profile or potential energy diagram — shows how the potential energy of a chemical system changes as a reaction proceeds. Potential energy is plotted on the vertical axis and the reaction progress, or reaction coordinate, runs along the horizontal axis from reactants on the left to products on the right. The curve starts on a flat plateau at the reactant energy, climbs to a peak, and then descends to a plateau at the product energy. The height of that curve at any point represents the energy the collection of atoms holds as old bonds break and new bonds form. Because the x-axis is a measure of progress rather than time or concentration, it has no numeric scale — only direction matters. These diagrams let you read off, at a glance, how much energy a reaction needs to get started and whether it releases or absorbs energy overall.

Activation energy and the transition state

To react, molecules must first collide with enough energy and the right orientation to reach an unstable, high-energy arrangement called the transition state — the peak of the curve. The energy required to climb from the reactant level up to that peak is the activation energy, written Ea.
Activation energy is the barrier every reaction has to clear, which is why some thermodynamically favorable reactions still proceed slowly at room temperature: the molecules rarely have enough energy to reach the top. A higher peak means a larger Ea and a slower reaction; a lower peak means the barrier is easier to cross.
The transition state itself is fleeting and cannot be isolated. It sits at the maximum of the curve where bonds are partially broken and partially formed. In this tool the peak energy is simply the reactant energy plus the activation energy, and it is marked with a labeled dot at the top of the curve.

Exothermic vs endothermic reactions (ΔH)

The overall energy change of a reaction is the enthalpy change, ΔH, equal to the product energy minus the reactant energy. Its sign tells you whether energy is released or absorbed.
In an exothermic reaction the products sit lower than the reactants, so ΔH is negative and energy is released to the surroundings — the reaction gives off heat. In an endothermic reaction the products sit higher than the reactants, ΔH is positive, and energy is absorbed from the surroundings. This tool detects the type automatically from the two energy levels you enter and draws the ΔH arrow pointing down for exothermic and up for endothermic.
Note that ΔH and Ea are independent: a reaction can be strongly exothermic yet still have a large activation barrier, which is why fuels can sit stably in air until a spark provides the energy to get over the peak.

Catalysts and lower activation energy

A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy — a lower peak on the diagram. It does not change the reactant or product energies, so the overall ΔH stays exactly the same; only the barrier between them is reduced.
On a reaction coordinate diagram a catalyzed pathway is drawn as a second curve sharing the same start and end levels but with a shorter climb to a lower transition state. Toggle "Show catalyzed pathway" in the tool to overlay it and compare the two barriers side by side.
Because more molecules have enough energy to clear a lower barrier at any given temperature, lowering Ea can dramatically increase the reaction rate. Enzymes are biological catalysts that work exactly this way, cutting activation energies so reactions can run quickly at body temperature.

Multi-step reactions and intermediates

Many reactions happen in more than one elementary step. A two-step reaction has two transition states — two peaks — separated by a valley. The species that sits in that valley is a reaction intermediate: a real, if short-lived, molecule that forms after the first step and is consumed in the second.
An intermediate is fundamentally different from a transition state. A transition state is a maximum on the energy curve and cannot be isolated, while an intermediate is a local minimum — it is stable enough, at least briefly, to have its own energy level. The taller of the two peaks corresponds to the slowest, rate-determining step.
Switch on "Two-step (with intermediate)" to draw a diagram with two transition states and a labeled intermediate in the dip between them. You can set the intermediate energy and the second activation energy independently to model the shape of the mechanism.

Frequently Asked Questions

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What is a reaction coordinate diagram?

Activation energy and the transition state

To react, molecules must first collide with enough energy and the right orientation to reach an unstable, high-energy arrangement called the transition state — the peak of the curve. The energy required to climb from the reactant level up to that peak is the activation energy, written Ea.

Activation energy is the barrier every reaction has to clear, which is why some thermodynamically favorable reactions still proceed slowly at room temperature: the molecules rarely have enough energy to reach the top. A higher peak means a larger Ea and a slower reaction; a lower peak means the barrier is easier to cross.

The transition state itself is fleeting and cannot be isolated. It sits at the maximum of the curve where bonds are partially broken and partially formed. In this tool the peak energy is simply the reactant energy plus the activation energy, and it is marked with a labeled dot at the top of the curve.

Exothermic vs endothermic reactions (ΔH)

The overall energy change of a reaction is the enthalpy change, ΔH, equal to the product energy minus the reactant energy. Its sign tells you whether energy is released or absorbed.

In an exothermic reaction the products sit lower than the reactants, so ΔH is negative and energy is released to the surroundings — the reaction gives off heat. In an endothermic reaction the products sit higher than the reactants, ΔH is positive, and energy is absorbed from the surroundings. This tool detects the type automatically from the two energy levels you enter and draws the ΔH arrow pointing down for exothermic and up for endothermic.

Note that ΔH and Ea are independent: a reaction can be strongly exothermic yet still have a large activation barrier, which is why fuels can sit stably in air until a spark provides the energy to get over the peak.

Catalysts and lower activation energy

A catalyst speeds up a reaction by providing an alternative pathway with a lower activation energy — a lower peak on the diagram. It does not change the reactant or product energies, so the overall ΔH stays exactly the same; only the barrier between them is reduced.

On a reaction coordinate diagram a catalyzed pathway is drawn as a second curve sharing the same start and end levels but with a shorter climb to a lower transition state. Toggle "Show catalyzed pathway" in the tool to overlay it and compare the two barriers side by side.

Because more molecules have enough energy to clear a lower barrier at any given temperature, lowering Ea can dramatically increase the reaction rate. Enzymes are biological catalysts that work exactly this way, cutting activation energies so reactions can run quickly at body temperature.

Multi-step reactions and intermediates

Many reactions happen in more than one elementary step. A two-step reaction has two transition states — two peaks — separated by a valley. The species that sits in that valley is a reaction intermediate: a real, if short-lived, molecule that forms after the first step and is consumed in the second.

An intermediate is fundamentally different from a transition state. A transition state is a maximum on the energy curve and cannot be isolated, while an intermediate is a local minimum — it is stable enough, at least briefly, to have its own energy level. The taller of the two peaks corresponds to the slowest, rate-determining step.

Switch on "Two-step (with intermediate)" to draw a diagram with two transition states and a labeled intermediate in the dip between them. You can set the intermediate energy and the second activation energy independently to model the shape of the mechanism.

Frequently Asked Questions