NEET ChemistryUpdated 19 Oct 2026

Chemical Kinetics: NEET PYQs and weightage

Chemical Kinetics carries 4.5 of 100 Chemistry marks in NEET by past-paper share: 32 of the 707 tagged NEET Chemistry PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 6 of 26 Chemistry chapters.

Take the 25-question Chemical Kinetics test Formula sheet ↓All NEET Chemistry chapters

4.5/100 Weight in Chemistry

Exam importance (4/5, by past-paper share)

32 NEET PYQs

411 Practice questions

366 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Chemistry PYQs in the bank (32 of 707), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Chemical Kinetics: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

First order integrated law
$k = \frac{2.303}{t} lo g \frac{[ R ] _{0}}{[ R ]}$
$[R] = [R]_{0} e^{- k t}$
Use it when: a first order reaction gives you concentrations (or amounts) at two times and asks for $k$ , $t$ or $[R]$
First order half-life
$t_{1/2} = \frac{0.693}{k} = \frac{ln 2}{k} (independent of [R]_{0})$
Use it when: a first order or radioactive decay question gives $k$ and asks for $t_{1/2}$ , or the reverse
Arrhenius equation
$k = A e^{- E_{a} / R T}$
$ln k = ln A - \frac{E _{a}}{R T} (plot ln k vs 1/ T : slope = - E_{a} / R, intercept = ln A)$
Use it when: you need to link $k$ , $A$ , $E_{a}$ and $T$ at a single temperature ( $E_{a}$ in $J mol^{- 1}$ with $R = 8.314 J mol^{- 1} K^{- 1}$ , $T$ in kelvin)
Two-temperature Arrhenius
$lo g \frac{k _{2}}{k _{1}} = \frac{E _{a}}{2.303 R} \times \frac{T _{2} - T _{1}}{T _{1} T _{2}}$
Use it when: $k$ (or the rate) is known at two temperatures and $E_{a}$ or the new $k$ is asked
Rate in terms of each species
$for a A + b B \to c C + d D :$
$rate = - \frac{1}{a} \frac{Δ [ A ]}{Δ t} = - \frac{1}{b} \frac{Δ [ B ]}{Δ t} = + \frac{1}{c} \frac{Δ [ C ]}{Δ t} = + \frac{1}{d} \frac{Δ [ D ]}{Δ t}$
Use it when: you are converting the rate of one species into the rate of the reaction or of another species
Rate law and order
$rate = k [A]^{x} [B]^{y}$
$overall order n = x + y (x and y come from experiment)$
Use it when: an initial-rate table is given (change one concentration, keep the other fixed, compare rates)
Units of k
$units of k = (mol L^{- 1})^{1 - n} s^{- 1}$
$zero order: mol L^{- 1} s^{- 1}$
$first order: s^{- 1}$
$second order: L mol^{- 1} s^{- 1}$
Use it when: you have to read the order from the units of $k$ , or the other way round
Zero order integrated law
$[R] = [R]_{0} - k t$
$k = \frac{[ R ] _{0} - [ R ]}{t} (plot [R] vs t : slope = - k, intercept = [R]_{0})$
Use it when: the reaction is zero order, for example $N H_{3}$ decomposing on a hot Pt surface at high pressure
Zero order half-life
$t_{1/2} = \frac{[ R ] _{0}}{2 k}$
$t_{1/2} \propto [R]_{0}$
Use it when: a zero order $t_{1/2}$ is asked, or $t_{1/2}$ changes as $[R]_{0}$ changes (that change means the reaction is not first order)
First order between two instants
$k = \frac{2.303}{t _{2} - t _{1}} lo g \frac{[ R ] _{1}}{[ R ] _{2}}$
Use it when: concentrations are given at two later times instead of at $t = 0$
First order gas reaction from total pressure
$for A (g) \to B (g) + C (g) :$
$k = \frac{2.303}{t} lo g \frac{p _{i}}{2 p _{i} - p _{t}}$
Use it when: only the initial pressure $p_{i}$ and the total pressure $p_{t}$ at time $t$ are given (first write $p_{A}$ from the stoichiometry)
First order completion time
$t_{99.9%} = \frac{6.909}{k} \approx 10 \times t_{1/2}$
Use it when: a question asks for the time to near-complete reaction in terms of $t_{1/2}$
Fraction of molecules with energy ≥ Ea
$fraction = e^{- E_{a} / R T}$
Use it when: $E_{a}$ and $T$ are given and the fraction of effective-energy molecules is asked
Collision theory
$rate = P Z_{A B} e^{- E_{a} / R T} (Z_{A B} = collision frequency, P = steric or orientation factor)$
Use it when: a question is about effective collisions, or about why $A$ depends on collision frequency and orientation

Trap

Taking the order from the coefficients in the balanced equation. Order is found only from experiment, and it can be 0 or a fraction. For example, CHCl₃ + Cl₂ has rate = k[CHCl₃][Cl₂]^½. Molecularity applies only to an elementary step and is always a whole number from 1 to 3.

How does NEET ask Chemical Kinetics?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1ChemistryNEET UG PYQOrder and Molecularity of Reactions

Try right here · No sign-in

When initial concentration of a reactant is doubled in a reaction, it's half-life period is not affected. The order of the reaction is:

Answer key (C) & worked solution

Correct answer: Option C

t_{1/2} \propto [A]_{0}^{1 - n}

For first order reaction, half-life period does not depend upon initial concentration.

Q2ChemistryNEET UG PYQArrhenius Equation

What is the activation energy for a reaction if its rate doubles when the temperature is raised from 20ºC to 35ºC ? (R = 8.314 J mol

^{- 1}

^{- 1}

)

A342 KJ mol

^{- 1}

B269 KJ mol

^{- 1}

C34.7 KJ mol

^{- 1}

D15.1 KJ mol

^{- 1}

Answer key (C) & worked solution

Correct answer: Option C

lo g \frac{k _{2}}{k _{1}} = \frac{E _{a}}{2.303 R} [\frac{T _{2} - T _{1}}{T _{1} . T _{2}}]

lo g 2 = \frac{E _{a}}{2.303 \times 8.314} [\frac{308 - 293}{293 \times 308}]

E a = \frac{0.301 \times 2.303 \times 8.314 \times 293 \times 308}{15} = 34.67 k J m o l^{- 1}

Q3ChemistryNEET UG PYQRate of a Chemical Reaction

For the chemical reaction

N_{2} (g) + 3 H_{2} (g) ⇌ 2 N H_{3} (g)

the correct option is:

- \frac{d [ N _{2} ]}{d t} = 2 \frac{d [ N H _{3} ]}{d t}

- \frac{d [ N _{2} ]}{d t} = \frac{1}{2} \frac{d [ N H _{3} ]}{d t}

3 \frac{d [ H _{2} ]}{d t} = 2 \frac{d [ N H _{3} ]}{d t}

- \frac{1}{3} \frac{d [ H _{2} ]}{d t} = - \frac{1}{2} \frac{d [ N H _{3} ]}{d t}

Answer key (B) & worked solution

Correct answer: Option B

N_{2} + 3 H_{2} ⇌ 2 N H_{3}

Rate of reaction is given as

- \frac{d [ N _{2} ]}{d t} = - \frac{1}{3} \frac{d [ H _{2} ]}{d t} = + \frac{1}{2} \frac{d [ N H _{3} ]}{d t}

Q4ChemistryNEET UG PYQDifferential and Integral Forms of Rate Law

If the half-life (t1/2) for a first order reaction is 1 minute, then the time required for 99.9% completion of the reaction is closest to

A5 minutes

B10 minutes

C2 minutes

D4 minutes

Answer key (B) & worked solution

Correct answer: Option B

t_{99.9} = 10 \times t_{1/2}

t_{99.9} = 10 min

Q5ChemistryNEET UG PYQRate Constant and Its Units

Match List I with List II :

List-I (Order of reaction)

List-II (Unit of rate constant)

A.

Zero order

I.

$\mathrm{mol}^{-1} \mathrm{~L} \mathrm{~s}^{-1}$

B.

First order

II.

$\mathrm{mol}^{-2} \mathrm{~L}^{2} \mathrm{~s}^{-1}$

C.

Second order

III.

s^{- 1}

D.

Third order

IV.

mol L^{- 1} s^{- 1}

Choose the correct answer from the options given below :

AA-IV, B-III, C-II, D-I

BA-I, B-II, C-III, D-IV

CA-IV, B-III, C-I, D-I

DA-IV, B-II, C-I, D-III

Answer key (C) & worked solution

Correct answer: Option C

Unit for rate constant of

n^{th}

order reaction

= (\frac{m o l}{L})^{1 - n} s^{- 1}

For zero order reaction

\Rightarrow n = 0

; unit

\Rightarrow mol L^{- 1} s^{- 1}

For first order reaction

\Rightarrow n = 1

; unit

\Rightarrow s^{- 1}

For second order reaction

\Rightarrow n = 2

; unit

\Rightarrow mol^{- 1} L s^{- 1}

For third order reaction

\Rightarrow n = 2

; unit

\Rightarrow mol^{- 2} L^{2} s^{- 1}

Q6ChemistryNEET UG PYQDifferential and Integral Forms of Rate Law

If the rate constant of a reaction is 0.03 s–1, how much time does not take for 7.2 mol L–1 concentration of the reactant to get reduced to 0.9 mol L–1 (Given: log 2 = 0.301)

A210 s

B21.0 s

C69.3 s

D23.1 s

Answer key (C) & worked solution

Correct answer: Option C

Rate constant k = 0.03 s–1 Initial concentration [A]

_{0}

= 7.2 mol L–1 Final concentration [A] = 0.9 mol L–1 log 2 = 0.301 For a first-order reaction, the integrated rate law is: ln [A] – ln [A]

_{0}

= –kt

t = \frac{1}{k} \times 2.303 lo g \frac{[ A ] _{0}}{[ A ]}

t = \frac{1}{0 .03} \times 2.303 lo g \frac{7.2}{0 .9}

t = \frac{1}{0 .03} \times 2.303 lo g 8

t = \frac{1}{0 .03} \times 2.303 \times lo g 2

t = \frac{1}{0 .03} \times 2.303 \times 0.3010 = 69.3 s

Q7ChemistryNEET UG PYQDifferential and Integral Forms of Rate Law

For a first order reaction A → Products, initial concentration of A is 0.1 M, which becomes 0.001M after 5 minutes. Rate constant for the reaction in min

^{- 1}

A1.3818

B0.9212

C0.4606

D0.2303

Answer key (B) & worked solution

Correct answer: Option B

K = \frac{2.303}{t} lo g (\frac{[ A _{0} ]}{[ A ]})

= \frac{2.303}{t} lo g (\frac{0.1}{0 .001})

= \frac{2.303}{5} lo g 1 0^{2}

= 0.9212

Q8ChemistryNEET UG PYQOrder and Molecularity of Reactions

The decomposition of phosphine (PH

_{3}

) on tungsten at low pressure is a first-order reaction. It is because the

ARate is inversely proportional to the surface coverage

BRate is independent of the surface coverage

CRate of decomposition is very slow

DRate is proportional to the surface coverage

Answer key (D) & worked solution

Correct answer: Option D

The decomposition of PH

_{3}

on tungsten at low pressure is a first order reaction because rate is proportional to the surface coverage.

Which topics in Chemical Kinetics carry the most questions?

The 12 busiest of 13 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Arrhenius Equation	10	69
Differential and Integral Forms of Rate Law	8	76
Order and Molecularity of Reactions	5	66
Rate of a Chemical Reaction	3	67
Rate Law	2	36
Introduction to Chemical Kinetics	2	4
Rate Constant and Its Units	1	28
Determination of Order of Reaction	1	15
Some Important First Order Reactions	0	21
Activated Complex Theory	0	10
Elementary and Complex Reactions	0	10
Collision Theory	0	8

Why does Chemical Kinetics show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Chemical Kinetics, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Chemical Kinetics?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Chemical Kinetics test

Chapters either side of Chemical Kinetics by weight

Solutions Weight 5.7/100 Alcohols, Phenols, and Ethers Weight 5.0/100 d- and f-Block Elements Weight 4.4/100 Electrochemistry Weight 4.2/100

Chemical Kinetics: NEET PYQs and weightage

Chemical Kinetics: formula sheet for NEET

First order integrated law

First order half-life

Arrhenius equation

Two-temperature Arrhenius

Rate in terms of each species

Rate law and order

Units of k

Zero order integrated law

Zero order half-life

First order between two instants

First order gas reaction from total pressure

First order completion time

Fraction of molecules with energy ≥ Ea

Collision theory

How does NEET ask Chemical Kinetics?

Which topics in Chemical Kinetics carry the most questions?

Why does Chemical Kinetics show "–" until you answer 3 questions?

What happens when you test Chemical Kinetics?

Chapters either side of Chemical Kinetics by weight