IAL Chem Unit 4 Kinetics Cheat Sheet

A Education › Chemistry cheat sheet in English by anupamabalaji

Key Definitions, Graphs, formulae.

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PRs

Key Definitions

Term	Definition
Rate of Reaction	Change in concentration of a reactant or product per unit time.
Rate Equation	Rate = k [A]^m [B]ⁿ where m, n are the orders of the reaction.
Order of Reaction	The power to which the concentration of a reactant is raised in the rate law
Overall Order	The sum of the powers (orders) of all reactants in the rate equation. Order = m+n.
Half-life (t_₁⁄₂)	Time taken for the concentration of a reactant to fall to half its value.
Rate Constant (k)	Proportionality constant in the rate equation; depends on temperature.
Activation Energy (Eₐ)	Minimum energy needed for a reaction to occur.
Adsorption	The binding of molecules to a surface (such as a catalyst), which increases reaction rate.
Desorption	The release of products from a catalyst surface after the reaction.

Arrhenius Equation

k=Ae^E_a/RT
Where
k = Chemical Reaction Rate
A = Pre-exponential factor
E_a = Activation Energy
R = Gas Constant
T = Temperature in Kelvin

Mechanisms: SN1 vs SN2

Feature	SN1	SN2
Steps	2 steps (carbocation formed)	1 step (simultaneous attack/leave)
Reactivity	Tertiary haloalkanes	Primary haloalkanes
Rate Law	rate = k[haloalkane]	rate = k[haloalkane][Nu⁻]
Steric Hindrance	Low (carbocation intermediate)	High (due to nucleophile approach)

SN1 & SN2

Experimental Techniques

Method	Measurement	Used For
Mass loss	Decreasing mass (gas released)	Rate of gas-producing reactions
Volume of gas	Gas syringe / upside-down cylinder	Gas evolution
Titration	Concentration vs time	Accurate kinetic data
Colorimetry	Absorbance vs concentration	Colored species (e.g. I₂ reaction)

Rate Laws & Integrated Rate Equations

Order	Rate Law	Half-life
Zero	rate = k	t_₁⁄₂ = [A]₀ / 2k
First	rate = k[A]	t_₁⁄₂ = ln2 / k
Second	rate = k[A]²	t_₁⁄₂ = 1 / (k[A]₀)

Graphs

Half Life

Rate Determining Step (RDS)

1. The slowest step in a mechanism controls the overall rate.
2. Only species involved up to RDS appear in the rate equation.
3. Powers in rate law = number of molecules in RDS.

Catalysis

Type	Phase	Example	Notes
Homogeneous	Same as reactants	Fe²⁺/Fe³⁺ in S₂O₈²⁻ + I⁻	Catalyst regenerated via redox steps
Heterogeneous	Different from reactants	Fe in Haber process	Provides surface, weakens bonds, speeds reaction

Catalysts lower the activation energy of a reaction by providing an alternate reaction route.

Adsorption (in Heterogeneous Catalysis)

Adsorption is when reactant molecules bind to active sites on the surface of a solid catalyst.

This:
1. Brings molecules close together, increasing collision frequency
2. Weakens bonds in the reactants, lowering activation energy
3. Allows for a faster reaction

After the reaction, products desorb (leave) from the surface, freeing the site for reuse.

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