Chem notesPhysicalKinetics
Independent topic page
Infer order from evidence rather than coefficients, select the matching integrated law, and reserve mechanism claims for elementary steps.
01. Rate is normalized by stoichiometric coefficients so every species reports one reaction rate. Reactant concentration decreases, hence the minus sign.
02. The differential rate law is empirical unless an elementary step is specified. Molecularity belongs only to an elementary step and is a positive integer.
03. Integrated laws, half-life dependence and linear plots are three fingerprints of order; use all available evidence for consistency.
04. Arrhenius separates collision frequency/orientation in A from the exponential activation barrier. A catalyst changes pathway and E_a, not ΔG° or equilibrium K.
05. Order is experimental evidence; molecularity is an elementary-step integer. Stoichiometric coefficients are not automatic rate exponents.
06. Integrated laws, half-life dependence and linear plots are a fingerprint triangle — demand consistency before naming the order.
07. Arrhenius and catalysis change how fast you approach equilibrium; they do not rewrite K or ΔG°. A catalyst lowers the barrier both ways.
Official · 2026
Official syllabus points for Chemical Kinetics only — not the full Physical portion map. Portion hub: Physical · Physical analysis.
No topic-specific exclusions flagged — finish the unit points below for Kinetics.
Source: https://jeeadv.ac.in/documents/jee-advanced-2026-syllabus.pdf
Exam focusZero/first order integrated laws, Arrhenius, catalysis ideas.
Syllabus points
Do / check
2020–2026 paper weight
Topic match inside parent portion Physical (49.8% of Chemistry tags). Stats below are portion backdrop; matched subtopics show where Chemical Kinetics sits.
Portion-wide type/difficulty mix lives on the Physical analysis — not repeated here so this page stays on Kinetics.
Cross-topic stems
Advanced rarely asks a chapter in isolation. These are tagged multi-idea Chemistry stems that touch Chemical Kinetics — practise the knowledge bridge, not only the single-chapter drill.
No tagged mixed stem matched this topic’s keywords yet. Still revise the joins listed under Trends, and scan the mixed joins board for Physical / Inorganic / Organic bridges.
Why methods matter
Order recognition determines the correct graph, half-life expression, units and integrated law.
Isolates one exponent without solving a simultaneous logarithmic system.
Do thisChoose two experiments where all but one concentration are unchanged.
Isolates one exponent without solving a simultaneous logarithmic system.
Doubling A at fixed B quadruples rate, so 2^m=4 and m=2.
A single noisy clue can mislead; three consistent signatures identify order.
Do thisCross-check integrated plot, k units and half-life dependence.
A single noisy clue can mislead; three consistent signatures identify order.
Constant half-life, linear ln[A] vs t and k in time⁻¹ all indicate first order.
Turns percent-completion wording into a clean logarithm or reciprocal.
Do thisSet [A]_t=f[A]_0 before using the integrated law.
Turns percent-completion wording into a clean logarithm or reciprocal.
For first order, 90% complete means f=0.10 and t=ln10/k.
Prevents deriving an unsupported rate law from the overall equation.
Do thisUse stoichiometric powers only for an elementary rate-determining step, eliminating intermediates when needed.
Prevents deriving an unsupported rate law from the overall equation.
A fast pre-equilibrium can express an intermediate in reactants before substitution into the slow-step rate.
Processed examples
Read the impact line first. Then notice which family/model was chosen. The solution is written the way your rough sheet should look in the hall.
A reactant falls from 0.80 M to 0.40 M in 20 min and to 0.20 M in 40 min. Identify order.
This stem rewards early recognition of the integrated rate-law identification model.
Model chosenRecognize constant half-life.
AnswerFirst order
Takeaway: Equal successive half-lives diagnose first order.
Doubling [A] quadruples rate; doubling [B] leaves rate unchanged. Find rate law.
This stem rewards early recognition of the initial-rate method model.
Model chosenTake pairwise rate ratios.
Answerr=k[A]²
Takeaway: Zero-order reactants disappear from the rate law.
For A⇌I (fast equilibrium, constants k₁ and k₋₁), followed by I+B→P (slow, k₂), derive the rate law.
This Advanced-level variation couples hidden constraints with the mechanism and steady state model.
Model chosenUse pre-equilibrium to eliminate I.
Answerr=(k₁k₂/k₋₁)[A][B]
Takeaway: Observed rate laws must not contain an unmeasured intermediate.
Reusable models
Advanced stems cluster. Name the family in 10–15s, write the fast model, then run the same path. Do not invent a new plan each time.
Looks likeConcentration or pressure data versus time
Fast modelTest the linear form or constant half-life signature.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeSeveral experiments with changed concentrations
Fast modelDivide rate equations pairwise.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeRate constants at two temperatures or catalyst effect
Fast modelUse the logarithmic two-temperature form.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeElementary steps, intermediate or observed rate law
Fast modelEliminate intermediates using pre-equilibrium or steady state.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Hall timing
Underline data, units, phase/standard-state labels and the exact quantity asked. Reject any formula whose assumptions are already violated.
Write the governing relation symbolically before substitution; define one basis, reference state, or extent variable if the stem mixes quantities.
Keep ratios and logarithms exact as long as possible. Carry signs, powers of ten and units on the rough sheet instead of repairing them later.
Check dimensions, limiting cases and chemical sense. For multi-correct, test every option independently rather than forcing one common conclusion.
After the model is locked
r=−(1/a)d[A]/dt=(1/p)d[P]/dt
aA→pP reaction-rate relation
[A]_t=[A]_0−kt; t₁/₂=[A]_0/(2k)
Rate independent of A over stated range
ln([A]_0/[A]_t)=kt; t₁/₂=ln2/k
First-order decay
1/[A]_t−1/[A]_0=kt; t₁/₂=1/(k[A]_0)
Rate=k[A]²
[k]=(concentration)^(1−n) time⁻¹ for overall order n
Order/unit checks
k=Ae^(−E_a/RT); ln k=ln A−E_a/(RT)
Temperature dependence
ln(k₂/k₁)=−E_a/R(1/T₂−1/T₁)
Find E_a or rate-constant ratio
rate=k[A][B]^m=k'[A] when [B]≈constant in large excess
One reactant buffered/in excess
Make it automatic