Multistep Reaction Energy Profile

Multistep Reaction Energy Profiles

• A multistep reaction is a chemical reaction that involves more than one elementary step or process.
• These steps can take place in a specific order, termed a reaction mechanism.
• Every elementary step of a multistep reaction has its own activation energy and transition state.

Complex Reactions and Intermediates

• An intermediate is a species that is formed during the reaction but gets utilized before the reaction is completed.
• Complex reactions usually involve intermediates - these are not reactants or products, but are substances produced and used up during the reaction sequence.
• Intermediates are typically unstable and reactive, they are formed in an early step and consumed in a later step of the reaction.

Energy Profile Diagram

• An energy profile diagram can be used to illustrate a multistep reaction.
• This diagram shows the potential energy of a reaction system as it progresses from reactants to products.
• The energy changes of all the steps are shown in one diagram.
• Each ‘hill’ or hump on the curve represents a different elementary step, their peak being the transition state, requiring a specific activation energy.

Transition States and Activation Energy

• The transition state is the highest energy configuration of a system during a reaction, shown as the peak of the energy hill.
• The height of the hill is the activation energy for that step - the minimum energy needed to initiate the reaction.

Reaction Rate Determining Step

• The slowest step in a multistep reaction is known as the rate-determining step.
• The activation energy of the rate-determining step is equal to the highest energy barrier, or peak, in the energy profile diagram.
• Understanding the rate-determining step helps chemists to predict how changes to conditions, such as temperature or concentration, will affect reaction rates.