Difference Between Activated Complex and Transition State

Main Difference – Activated Complex vs Transition State

A chemical reaction is a process that involves rearrangement of the molecular or ionic structure of a substance, as distinct from a change in physical form or a nuclear reaction. A chemical reaction may occur directly via a single step, or it may occur via several steps. Activated complex and transition state are two terms explained regarding a chemical reaction with multiple stages or steps. Activated complex refers to a collection of intermediate molecules formed during the progression of a chemical reaction. Here, the progression of the chemical reaction refers to the conversion of reactants into products. The transition state of a chemical reaction is intermediate with the highest potential energy. The main difference between activated complex and transition state is that activated complex refers to all possible intermediates whereas transition state refers to the intermediate with the highest potential energy.

Key Areas Covered

1. What is Activated Complex
     – Definition, Explanation
2. What is Transition State
     – Definition, Explanation
3. What is the Relationship Between Activated Complex and Transition State
4. What is the Difference Between Activated Complex and Transition State
     – Comparison of Key Differences

Key Terms: Activated Complex, Chemical Reaction, Intermediate, Products, Potential Energy, Reactants, Transition State

Difference Between Activated Complex and Transition State - Comparison Summary

What is Activated Complex

Activated complex refers to a collection of intermediate molecules formed during the progression of a chemical reaction. An activated complex is an unstable arrangement of atoms of the reactants. Hence, the intermediate arrangements or the activated complexes have a higher potential energy than reactants. Due to its instability, an activated complex exists for a very short time period.

Activated complex may or may not form the end products. This means, activated complexes sometimes go backward, giving the reactants back than going forward to form products. A chemical reaction involves breaking and forming of chemical bonds. Activated complex is formed when bonds break and form between different atoms.

Main Difference - Activated Complex vs Transition State

Figure 1: Different Chemical Reactions with Different Intermediates

But in order to break and form chemical bonds, energy should be provided to reactants. Therefore, reactants colloid with each other in proper orientation for the reaction to happen. These collisions form activated complexes.

What is Transition State

Transition state is the intermediate of a chemical reaction that comprises the highest potential energy. For chemical reactions that have only one intermediate, that intermediate is considered as the transition state. A chemical reaction with two or more steps has three stages: initial stage with only reactants, transition state with intermediates and the final stage with products. Therefore, the transition state refers to the stage where reactants are converted into products.

Difference Between Activated Complex and Transition State

Figure 2: Transition State

There is a high probability of the transition state to go forward to form products rather than falling back to form reactants again. In order to make a chemical reaction successful, reactant molecule should colloid with each other in proper orientation. The transition state or the intermediate with highest potential energy is highly unstable. Therefore, it does not exist for a long period of time. This makes it difficult to capture the transition state of a chemical reaction.

Activation Energy

Activation energy of a chemical reaction is the energy barrier that has to be overcome in order to obtain products from the reaction. It is the minimum energy required for a reactant to convert into a product. Therefore, activation energy equals the potential energy of the transition state of a chemical reaction.

Relationship Between Activated Complex and Transition State

  • When there is only one intermediate molecule in a chemical reaction, activated complex and the transition state are the same.

Difference Between Activated Complex and Transition State

Definition

Activated Complex: Activated complex refers to a collection of intermediate molecules formed during the progression of a chemical reaction.

Transition State: Transition state is the intermediate of a chemical reaction that comprises the highest potential energy.

Potential Energy

Activated Complex: Activated complex has a high potential energy than reactants.

Transition State: Transition state has the highest potential energy among other intermediate structures.

Product Formation

Activated Complex: Activated complex may form the end product of the reaction or can go backward forming reactants without giving products.

Transition State: Transition state has a high probability of forming the product rather than forming the reactants again.

Conclusion

Some chemical reactions occur via several steps. There are three main stages: initial stage with reactants, transition state with intermediate molecules and final stage with products. Activated complex and transition state are two terms explained regarding this type of chemical reactions. The main difference between activated complex and transition state is that activate complex refers to all possible intermediates whereas transition state refers to the intermediate with the highest potential energy.

References:

1. Helmenstine, Anne Marie. “What an Activated Complex Means in Chemistry.” ThoughtCo, Available here.
2. “Transition state.” Wikipedia, Wikimedia Foundation, 9 Oct. 2017,  Available here.
3. “Activated complex.” Wikipedia, Wikimedia Foundation, 29 Oct. 2017, Available here.

Image Courtesy:

1. “Reaction Co-ordinate Diagrams for reactions with 0, 1, 2 intermediates” By AimNature – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Rxn coordinate diagram 5″ By Chem540grp1f08 – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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