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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)

Activation Energy and Maxwell–Boltzmann Distributions

Specification Reference R2.2.4

Quick Notes

  • Activation energy (Ea) is the minimum energy needed for a reaction to occur.
  • Only particles that collide with energy equal to or greater than Ea can react.
  • A Maxwell–Boltzmann distribution shows the spread of particle energies in a sample.
  • Increasing temperature:
    • Shifts the curve right
    • Increases the number of particles with E ≥ Ea
    • Results in a faster reaction rate

Full Notes

What Is Activation Energy (Ea)?

Activation energy is the minimum kinetic energy that reactant particles must have to successfully collide and form products.

If the kinetic energy is less than Ea, the particles do not react, even if they collide.

Reaction Profile Diagrams

Reaction profile diagrams show how the energy of reactants change as they turn into products.

IB Chemistry exothermic reaction profile diagram showing reactants at higher energy, products at lower energy, and activation energy hump. IB Chemistry endothermic reaction profile diagram showing reactants at lower energy, products at higher energy, and activation energy hump.

Activation energy is the distance between the energy of the starting reactants and the highest point of energy (the ‘hump’) on the curve.

Maxwell–Boltzmann Distribution Curve

The Maxwell–Boltzmann distribution is a graph that shows how available kinetic energy is spread out and shared amongst molecules of a gas.

It helps explain why:

IB Chemistry Maxwell–Boltzmann distribution curve showing particle energy spread, peak at most probable energy, and area representing total molecules.

Features of the curve:

Effect of Temperature on the Distribution

Increasing temperature shifts the curve right and lowers the peak.

IB Chemistry Maxwell–Boltzmann distribution curve at higher temperature, showing shift right and more molecules with energy above activation energy.

More molecules have energy ≥ Ea, increasing the rate of successful collisions. The total number of molecules stays the same (area under the curve is unchanged).

Summary