Activated complex

Activated Complex

Diagram of an activated complex in a chemical reaction.

The activated complex is a transient structure that forms during the course of a chemical reaction. It represents the highest energy state of the system and is a critical concept in the study of reaction kinetics. The activated complex is often referred to as the "transition state" of the reaction.

Formation

During a chemical reaction, reactant molecules must collide with sufficient energy and proper orientation to form an activated complex. This energy is known as the activation energy, which is the minimum energy required to initiate a reaction. The activated complex is formed at the peak of the energy barrier that separates reactants from products.

Characteristics

The activated complex is characterized by its high energy and instability. It exists for a very short period of time, typically on the order of femtoseconds (10^-15 seconds). Because of its transient nature, the activated complex cannot be isolated or directly observed. Instead, its properties are inferred from the study of reaction rates and the use of theoretical models such as transition state theory.

Transition State Theory

Transition state theory provides a framework for understanding the formation and decomposition of the activated complex. According to this theory, the rate of a chemical reaction is proportional to the concentration of the activated complex and the frequency with which it decomposes to form products. The theory also introduces the concept of the reaction coordinate, which is a path that represents the progress of the reaction from reactants to products through the transition state.

Energy Profile

The energy profile of a chemical reaction can be depicted in a diagram that shows the energy changes as the reaction progresses. The activated complex is located at the highest point on this energy profile, representing the energy barrier that must be overcome for the reaction to proceed. The difference in energy between the reactants and the activated complex is the activation energy.

Role in Catalysis

Catalysts play a crucial role in lowering the activation energy of a reaction, thereby facilitating the formation of the activated complex. By providing an alternative reaction pathway with a lower energy barrier, catalysts increase the rate of reaction without being consumed in the process. This is achieved by stabilizing the activated complex or by altering the reaction mechanism.

Related Pages

• Chemical kinetics
• Reaction mechanism
• Catalysis
• Activation energy
• Transition state theory