AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

R2.2 - How fast? The rate of chemical change

2.2.1 Rate of Reaction 2.2.2 Collision Theory 2.2.3 Factors Affecting Reaction Rate 2.2.4 Activation Energy and Temperature 2.2.5 Catalyst and Activation Energy 2.2.6 Reaction Mechanism and Intermediates (AHL) 2.2.7 Energy Profile and Rate Determining Step (AHL) 2.2.8 Molecularity in Reaction Mechanism (AHL) 2.2.9 Rate Equations and Experimental Data (AHL) 2.2.10 Reaction Orders and Graphs (AHL) 2.2.11 Rate Constant, K (AHL) 2.2.12 Arrhenius Reaction and Temperature (AHL) 2.2.13 Arrhenius Factor and Activation Energy (AHL)

Energy Profiles and Transition States in Multistep Reactions HL Only

Specification Reference R2.2.7

Quick Notes:

  • Energy profiles show energy changes as reactants turn into products.
  • Multistep reactions have multiple peaks and valleys:
    • Each peak = a transition state
    • Each valley = an intermediate
  • The highest peak = rate-determining step (RDS).
  • Activation energy (Ea) is the energy difference between reactants and the peak of the step.
  • Profiles help link kinetic data (reaction rate) to the mechanism.

Full Notes:

For an introduction to energy profiles and the basics, please see here.

In reactions that occur in multiple steps, the energy profile helps visualize the activation energies and transition states for each elementary step.

Key Features of Multistep Energy Profiles

IB Chemistry energy profile diagram showing multiple peaks for transition states and valleys for intermediates in a multistep reaction.

Rate-Determining Step (RDS)

The tallest peak corresponds to the step with the highest activation energy (Ea).

IB Chemistry reaction energy profile with multiple steps, showing the tallest peak as the rate-determining step.

See here for more detail.

Summary