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NEET 2027 · Chemistry · Chemical Kinetics · Topic 10 of 15

Collision Theory
Z, P and Threshold Energy

Tier 3 · moderate priority. Definitional, not numerical — NEET asks for the elementary idea only, so learn the two requirements, the threshold distinction, and the two drawbacks.

Tier · 3 — ModerateNCERT · §3.5Animations · 3Questions · 29Graph Qs · 4Assertion–Reason · 3

The big idea, in plain words

Molecules must actually meet before they can react. But meeting is not enough — they must meet hard enough and the right way round. Collision theory is simply that sentence turned into an equation.

Story track

Think about posting a letter through a letterbox while running past.

First, you have to reach the door at all. If you never get there, nothing happens. That is the collision frequency, Z — how often the meeting even occurs.

Second, you must be moving fast enough to push the flap open. A gentle tap bounces off. That is the energy requirement, and it is where activation energy comes in.

Third — and this is the part people forget — you must be holding the letter the right way round. Arrive at full speed holding the letter sideways and it simply will not go in. That is the orientation requirement, and it is what the steric factor P accounts for.

So three hurdles: meet, meet hard, meet correctly. A collision that clears all three is called an effective collision, and only effective collisions produce products.

Building the equation

Maths track

For a bimolecular elementary reaction A + B → Products, the first version of the theory says:

Rate = ZAB · e^(−Ea/RT)

Comparing this with the Arrhenius equation k = A·e^(−Ea/RT) shows that A is related to the collision frequency. That comparison is itself a standard exam question.

This version works well for atoms and simple molecules. For complex molecules it over-predicts the rate — real reactions are slower than it says. The reason is orientation, so a correction factor is added:

Rate = P · ZAB · e^(−Ea/RT)

P is the probability or steric factor. It accounts for the fact that in a collision, molecules must be properly oriented. P is a fraction between 0 and 1, and it is smaller for bulkier, more awkwardly shaped molecules.

The orientation picture — NCERT's own example

Formation of methanol from bromoethane depends on how the reactant molecules are lined up:

CH₃Br + OH⁻ → CH₃OH + Br⁻
The point to carry away. Energy alone is not sufficient. A violently energetic collision in the wrong geometry produces nothing at all. This is why P exists, and it is the single most examined idea from this section.

Threshold energy versus activation energy — the distinction that gets tested

Threshold energy = Activation energy + energy already possessed by the reacting species

NCERT states this as a footnote, which makes it easy to skim past — and precisely because of that, it appears regularly in question papers. The two are not synonyms.

Effective collisions — the full definition

NCERT: collisions in which molecules collide with sufficient kinetic energy (called threshold energy) and proper orientation, so as to facilitate breaking of bonds between reacting species and formation of new bonds to form products, are called effective collisions.

Note that both conditions appear in the definition. A question offering only one of them as the criterion is testing whether you noticed.

What the theory gets wrong

NCERT is explicit that collision theory has drawbacks:

Real molecules are not billiard balls — they have shapes, flexible bonds and internal vibrations. The steric factor P is essentially a patch applied to a model that does not know molecules have shapes.

Scope note for NEET. The syllabus asks for an elementary idea of collision theory only. You will not be asked to calculate Z or to derive P numerically. Learn the definitions, the two requirements for an effective collision, the threshold-versus-activation distinction, and the drawbacks. That is the whole examinable content.

Beyond the textbook

Why Z rises only slightly with temperature. Collision frequency goes as the square root of absolute temperature, so a 10 K rise near room temperature increases Z by well under 2%. Yet the rate roughly doubles. This confirms that the exponential energy factor, not the collision frequency, is what temperature acts on — a useful cross-check against the Arrhenius unit.
Typical size of P. For reactions between simple atoms P is close to 1. For reactions between large organic molecules P can be 10⁻⁵ or smaller — meaning fewer than one in a hundred thousand sufficiently energetic collisions is correctly oriented. Not in NCERT, but it makes the concept concrete.
Where the theory was superseded. Transition state theory (activated complex theory) replaces the hard-sphere picture with a proper treatment of the activated complex. NCERT mentions that you will study more on other theories in higher classes.

See it move — 3 animations

The first animation carries the key idea of the unit. Fire it at 0° and again at 180° and the reason P exists becomes obvious.

ANIM 1
Same energy, different geometry, opposite outcome

Two collisions carrying identical energy. Slide the approach angle from a back-side attack to a bromine-end attack and press fire. One forms products; the other bounces straight off. Nothing about the energy changed — only the geometry. This is NCERT's Fig. 3.12 made moving, and it is the entire justification for the steric factor P.

ANIM 2
Two filters, applied in sequence

Start with a thousand collisions per second. The energy filter removes most of them. The orientation filter removes most of what remains. Only the green bar produces products. Slide both filters and watch how quickly a large collision count collapses into a handful of effective ones — which is why reactions are far slower than collision counts alone would suggest.

ANIM 3
Threshold energy is not activation energy
Energy

The dashed black line is the threshold — the total energy needed, and it never moves. The green block is the energy the molecules already carry. The red block between them is the activation energy, the shortfall they must still make up. Slide the green block upward and watch the red block shrink while the threshold stays put. NCERT puts this in a footnote, which is exactly why it keeps appearing in papers.

Formula sheet

This unit is definitional. Learn the two requirements for an effective collision, the threshold-versus-activation distinction, and the two drawbacks — that covers essentially everything NEET asks here.

Quantity / situationFormulaWhen you use it
Collision frequency Znumber of collisions per second per unit volume of the reaction mixtureNCERT definition — learn the wording
Simple collision theoryRate = Z_AB · e^(−Ea/RT)Works for atoms and simple molecules
With steric factor ★Rate = P · Z_AB · e^(−Ea/RT)Needed for complex molecules
Steric factor Pprobability factor accounting for correct orientationA fraction between 0 and 1
Link to Arrheniuscomparing with k = A·e^(−Ea/RT) shows A relates to collision frequencyStandard exam question
Effective collision ★sufficient energy AND proper orientationBoth conditions required
Threshold energy ★= activation energy + energy already possessed by reacting speciesNCERT footnote; frequently tested
Energy factore^(−Ea/RT) = fraction with energy ≥ EaSame factor as in Arrhenius
Orientation exampleCH₃Br + OH⁻ : back-side attack works, bromine-end attack does notNCERT Fig. 3.12
Who developed itMax Trautz and William Lewis, 1916–18Based on the kinetic theory of gases
Drawback 1treats atoms and molecules as hard spheresNCERT states this
Drawback 2ignores their structural aspectP is a patch for this omission
NEET scopeelementary idea only — no numerical treatment of Z or PDefinitions and concepts, not calculations
Z and temperature — gapZ ∝ √T, so it rises only slightlyConfirms the exponential does the work

29 NEET-type questions with worked solutions

Four graph questions and three assertion–reason questions are included, marked by their coloured left borders. Questions tagged PYQ pattern follow forms that have appeared in NEET/AIPMT papers or come directly from NCERT exercises — exact year attributions are deliberately omitted rather than guessed.

Q01PYQ pattern

The number of collisions per second per unit volume of the reaction mixture is known as:

Given

Definition question

Asked

Name of the quantity

Concept

Direct recall of NCERT's definition.

Formula

Rate = Z_AB · e^(−Ea/RT)

Baby steps
  1. NCERT defines collision frequency, symbol Z, in exactly these words.
  2. It measures how often collisions occur, before any energy or orientation requirement is applied.
  3. It is one of the two factors in the collision theory rate expression.

Answer · (a) collision frequency

Q02PYQ pattern

According to collision theory, for a collision to be effective the molecules must have:

Given

Requirements for an effective collision

Asked

The correct condition

Concept

Both conditions appear in NCERT's definition; either alone is insufficient.

Formula

Rate = P · Z_AB · e^(−Ea/RT)

Baby steps
  1. NCERT defines effective collisions as those with sufficient kinetic energy and proper orientation.
  2. The energy requirement is captured by e^(−Ea/RT).
  3. The orientation requirement is captured by the steric factor P.
  4. Both factors appear in the rate expression, so both conditions must be satisfied.

Answer · (a) sufficient energy and proper orientation

Shortcut · Options offering only one condition are always wrong here. Both are required.
Q03PYQ pattern

The steric factor P in the expression Rate = P·Z_AB·e^(−Ea/RT) accounts for:

Given

Rate = P·Z_AB·e^(−Ea/RT)

Asked

What P accounts for

Concept

P was introduced because energy alone over-predicts the rate for complex molecules.

Formula

Rate = P·Z_AB·e^(−Ea/RT)

Baby steps
  1. Z accounts for how often collisions occur.
  2. The exponential accounts for how many collisions are energetic enough.
  3. Neither accounts for geometry, yet many energetic collisions still fail.
  4. P was introduced to take into account the fact that in a collision, molecules must be properly oriented.

Answer · (a) the requirement that colliding molecules be properly oriented

Q04PYQ pattern

Threshold energy is defined as:

Given

Definition question

Asked

Meaning of threshold energy

Concept

Threshold is the total required; activation energy is only the shortfall.

Formula

Threshold energy = Ea + energy possessed by reacting species

Baby steps
  1. Reactant molecules already carry some energy at the given temperature.
  2. To form the activated complex they must reach a certain total energy — the threshold.
  3. The extra they must still acquire is the activation energy.
  4. So threshold = activation energy + energy already possessed. NCERT states this as a footnote.

Answer · (a) activation energy plus the energy already possessed by the reacting species

Q05PYQ pattern

Comparing Rate = Z_AB·e^(−Ea/RT) with the Arrhenius equation shows that the Arrhenius factor A is related to:

Given

Rate = Z_AB·e^(−Ea/RT) and k = A·e^(−Ea/RT)

Asked

Physical meaning of A

Concept

Matching the two expressions term by term identifies A.

Formula

Rate = Z_AB·e^(−Ea/RT) versus k = A·e^(−Ea/RT)

Baby steps
  1. Both expressions contain the identical exponential factor e^(−Ea/RT).
  2. The remaining factor is Z in one and A in the other.
  3. Matching them identifies A with the collision frequency.
  4. Once the steric factor is included, A corresponds more precisely to P × Z.

Answer · (a) the collision frequency

Q06

Collision theory was developed by:

Given

Historical attribution

Asked

Who developed collision theory

Concept

Direct recall.

Formula

—

Baby steps
  1. NCERT states that collision theory was developed by Max Trautz and William Lewis in 1916–18.
  2. It is based on the kinetic theory of gases.
  3. Arrhenius and van't Hoff are associated with the temperature-dependence equation instead.
  4. Maxwell and Boltzmann developed the energy distribution used elsewhere in the chapter.

Answer · (a) Max Trautz and William Lewis

Q07PYQ pattern

A drawback of collision theory is that it:

Given

Limitations of collision theory

Asked

A stated drawback

Concept

The hard-sphere assumption is the theory's core simplification and its main weakness.

Formula

—

Baby steps
  1. NCERT states that collision theory considers atoms and molecules to be hard spheres and ignores their structural aspect.
  2. Real molecules have shapes, flexible bonds and internal motions.
  3. The steric factor P is essentially a correction for that omission.
  4. The theory does handle temperature dependence and does use activation energy, so those options are wrong.

Answer · (a) considers molecules as hard spheres and ignores their structural aspect

Q08PYQ pattern

In the reaction CH₃Br + OH⁻ → CH₃OH + Br⁻, an improperly oriented collision results in:

Given

Improper orientation in the bromomethane reaction

Asked

The outcome

Concept

Wrong geometry means no reaction at all, regardless of energy.

Formula

—

Baby steps
  1. NCERT's Fig. 3.12 shows that proper orientation leads to bond formation.
  2. Improper orientation makes the molecules simply bounce back.
  3. No products are formed at all — it is not a matter of a slower rate.
  4. This is the clearest demonstration that energy alone is insufficient.

Answer · (a) the molecules bouncing back with no products formed

Q09

Collision theory predicts rate constants accurately for:

Given

Accuracy of the simple collision theory

Asked

Where it works well

Concept

Simple species have few orientation constraints, so P is close to 1.

Formula

Rate = Z_AB·e^(−Ea/RT)

Baby steps
  1. NCERT states the equation predicts rate constants fairly accurately for reactions involving atomic species or simple molecules.
  2. For complex molecules significant deviations are observed.
  3. The reason is that not all collisions lead to products — orientation matters more for complex shapes.
  4. So the simple form works best where geometry is least restrictive.

Answer · (a) reactions involving atomic species or simple molecules

Q10

Which factor in collision theory corresponds to the fraction of molecules with energy equal to or greater than Ea?

Given

Rate = P·Z_AB·e^(−Ea/RT)

Asked

Which factor represents the energetic fraction

Concept

The exponential is the energy filter, exactly as in the Arrhenius equation.

Formula

fraction with E ≥ Ea = e^(−Ea/RT)

Baby steps
  1. Z counts all collisions regardless of energy.
  2. P accounts for orientation only.
  3. The exponential factor e^(−Ea/RT) represents the fraction of molecules with energies equal to or greater than Ea.
  4. NCERT states this explicitly when introducing the expression.

Answer · (a) e^(−Ea/RT)

Q11Graph

On the Maxwell–Boltzmann distribution shown, the shaded region beyond Ea represents:

EaKinetic energy
Given

Shaded tail beyond Ea on the distribution

Asked

What the shaded region represents

Concept

Energy is only the first filter; orientation is a separate second one.

Formula

Rate = P·Z·e^(−Ea/RT) — the shaded area corresponds to the exponential only

Baby steps
  1. The shaded area is the fraction of molecules with energy at least Ea, which is e^(−Ea/RT).
  2. These molecules have cleared the energy hurdle.
  3. But they have not yet cleared the orientation hurdle, which P accounts for separately.
  4. So not all of them will react — option (b) overstates it. Only P times this fraction gives effective collisions.

Answer · (a) the fraction of molecules energetic enough to react, but not necessarily correctly oriented

Shortcut · The distribution diagram shows only the energy filter. Orientation never appears on it.
Q12Graph

The bar chart shows all collisions, energetic collisions, and effective collisions. The reduction from the second bar to the third is caused by:

allenergeticeffective
Given

Three bars: all, energetic, effective

Asked

Cause of the final reduction

Concept

Each bar applies one further filter.

Formula

Rate = P · Z · e^(−Ea/RT)

Baby steps
  1. The first bar is Z, all collisions occurring.
  2. The reduction to the second bar is the energy filter e^(−Ea/RT), governed by activation energy.
  3. The further reduction to the third bar is the orientation filter, governed by P.
  4. So the final step is caused by the steric requirement, not by energy.

Answer · (a) the orientation requirement, quantified by P

Q13Graph

The diagram shows threshold energy and the energy already possessed by molecules. The labelled gap X is:

thresholdalready possessedX
Given

A diagram with threshold level, possessed level, and gap X between them

Asked

Identity of X

Concept

Activation energy is the shortfall between what molecules have and what they need.

Formula

Threshold = Ea + energy possessed ⟹ Ea = threshold − possessed

Baby steps
  1. The lower green block is the energy the molecules already carry.
  2. The upper level is the threshold — the total needed to form the activated complex.
  3. X is the gap between them, which is the extra energy that must still be acquired.
  4. That extra is the activation energy. Note the threshold is the whole height, not the gap.

Answer · (a) the activation energy

Shortcut · Threshold is the ceiling; activation energy is the climb from where you are to that ceiling.
Q14Graph

Two reactions have the same Z and the same Ea, but reaction P involves large organic molecules and reaction Q involves atoms. Which will have the larger rate?

P — bulky moleculesQ — atoms
Given

Same Z and Ea; one reaction with bulky molecules, one with atoms

Asked

Which is faster

Concept

With Z and Ea matched, only the steric factor distinguishes them.

Formula

Rate = P·Z·e^(−Ea/RT)

Baby steps
  1. Z and the exponential factor are identical for both reactions.
  2. The only remaining difference is P.
  3. Atoms are spherically symmetric, so almost any approach direction works and P approaches 1.
  4. Bulky molecules must line up precisely, so P is much smaller. Reaction Q is therefore faster.

Answer · (a) Q, because its steric factor P is closer to 1

Q15Assertion–Reason

Assertion (A): Not all collisions between reactant molecules lead to the formation of products.
Reason (R): Only collisions with sufficient energy and correct orientation are effective.

Given

Statements about collision effectiveness

Asked

Truth values and explanation

Concept

The two filters explain exactly why most collisions are fruitless.

Formula

Rate = P·Z·e^(−Ea/RT)

Baby steps
  1. Check A: NCERT states that all collisions do not lead to the formation of products. A is true.
  2. Check R: NCERT defines effective collisions as requiring both sufficient kinetic energy and proper orientation. R is true.
  3. Does R explain A? Yes — collisions failing either requirement produce nothing, which is why most are ineffective.
  4. The fraction of collisions that succeed is P × e^(−Ea/RT), typically a very small number.

Answer · (a) Both A and R are true and R is the correct explanation of A

Q16Assertion–Reason

Assertion (A): Threshold energy and activation energy are not the same quantity.
Reason (R): Threshold energy equals the activation energy plus the energy already possessed by the reacting molecules.

Given

Statements about threshold and activation energy

Asked

Truth values and explanation

Concept

The relation itself shows the two differ by the energy already present.

Formula

Threshold = Ea + energy possessed

Baby steps
  1. Check A: the two are distinct quantities, differing by the energy the molecules already carry. A is true.
  2. Check R: this is NCERT's footnote definition, stated exactly. R is true.
  3. Does R explain A? Yes — the relation shows they can only be equal if the molecules possess zero energy, which is never the case.
  4. This distinction is easy to skim past because it sits in a footnote, and it appears in papers for that very reason.

Answer · (a) Both A and R are true and R is the correct explanation of A

Q17Assertion–Reason

Assertion (A): Collision theory requires a steric factor P for reactions involving complex molecules.
Reason (R): The theory treats molecules as hard spheres and therefore takes no account of their shape.

Given

Statements about the steric factor and the hard-sphere model

Asked

Truth values and explanation

Concept

P compensates for a shortcoming built into the model's foundation.

Formula

Rate = P·Z·e^(−Ea/RT)

Baby steps
  1. Check A: NCERT notes significant deviations for complex molecules, which P was introduced to correct. A is true.
  2. Check R: NCERT lists the hard-sphere treatment and neglect of structural aspects as drawbacks. R is true.
  3. Does R explain A? Yes — because the model has no concept of molecular shape, orientation effects must be added back in through P.
  4. P is therefore best understood as a patch on a model that does not know molecules have shapes.

Answer · (a) Both A and R are true and R is the correct explanation of A

Q18

Collision theory is based on:

Given

Foundation of collision theory

Asked

Its basis

Concept

Direct recall.

Formula

—

Baby steps
  1. NCERT states that collision theory is based on the kinetic theory of gases.
  2. That theory treats particles as moving spheres undergoing elastic collisions.
  3. This foundation is also the source of the hard-sphere limitation.

Answer · (a) the kinetic theory of gases

Q19

For a bimolecular elementary reaction A + B → Products, collision theory expresses the rate as:

Given

A bimolecular elementary reaction

Asked

The collision theory rate expression

Concept

Collision frequency multiplied by the energetic fraction.

Formula

Rate = Z_AB·e^(−Ea/RT)

Baby steps
  1. The number of collisions per second is Z_AB.
  2. The fraction of those that are energetic enough is e^(−Ea/RT).
  3. Multiplying gives the number of energetically successful collisions per second.
  4. Including orientation, this becomes Rate = P·Z_AB·e^(−Ea/RT).

Answer · (a) Rate = Z_AB·e^(−Ea/RT)

Q20

The steric factor P has a value:

Given

Nature of the steric factor

Asked

Its range of values

Concept

P is a probability, so it cannot exceed 1.

Formula

Rate = P·Z·e^(−Ea/RT)

Baby steps
  1. P represents the probability that a collision has the correct orientation.
  2. A probability lies between 0 and 1 by definition.
  3. P close to 1 means orientation hardly matters, as for atoms.
  4. P much less than 1 means orientation is restrictive, as for bulky molecules. It reduces the predicted rate, never increases it.

Answer · (a) between 0 and 1

Shortcut · P was introduced because the simple theory over-predicts rates. A correction that reduces a prediction must be less than 1.
Q21

Which of these does collision theory NOT explain well?

Given

Strengths and weaknesses of collision theory

Asked

Where it performs poorly

Concept

The hard-sphere model has no way to represent molecular structure.

Formula

—

Baby steps
  1. The theory handles temperature dependence and activation energy successfully.
  2. It predicts rate constants fairly accurately for atomic species and simple molecules.
  3. For complex molecules significant deviations are observed, because structure is ignored.
  4. So it is structural complexity that the theory handles poorly.

Answer · (a) The behaviour of complex molecules with specific structural requirements

Q22

Increasing the temperature increases the rate mainly by increasing:

Given

Effect of temperature within collision theory

Asked

The dominant mechanism

Concept

Z rises only slightly with temperature, while the exponential rises sharply.

Formula

Rate = P·Z·e^(−Ea/RT) ; Z ∝ √T

Baby steps
  1. Collision frequency Z increases only as the square root of temperature, so a 10 K rise changes it by well under 2%.
  2. Yet the rate roughly doubles over that same rise.
  3. The exponential factor e^(−Ea/RT) is what responds sharply to temperature.
  4. P is a geometric property and does not depend on temperature, and Ea is fixed for a given pathway.

Answer · (a) the fraction of collisions with energy above Ea

Q23

An effective collision differs from an ordinary collision in that it:

Given

Definition of an effective collision

Asked

The distinguishing feature

Concept

Effectiveness is defined by the outcome — bonds actually change.

Formula

—

Baby steps
  1. NCERT's definition specifies collisions that facilitate breaking of bonds between reacting species and formation of new bonds to form products.
  2. An ordinary collision leaves the molecules chemically unchanged.
  3. The requirements for effectiveness are sufficient energy and proper orientation.
  4. Neither the number of molecules nor the presence of a catalyst is part of the definition.

Answer · (a) results in the breaking of old bonds and formation of new ones

Q24

If the steric factor P for a reaction is 10⁻⁵, this means that:

Given

P = 10⁻⁵

Asked

Interpretation

Concept

P is the fraction of energetic collisions that also have the right geometry.

Formula

Rate = P·Z·e^(−Ea/RT)

Baby steps
  1. P multiplies the already-filtered energetic collisions.
  2. A value of 10⁻⁵ means one in 100000 of those has the correct orientation.
  3. Such small values arise for large molecules with demanding geometric requirements.
  4. P says nothing about activation energy, collision frequency or order.

Answer · (a) only about one in a hundred thousand sufficiently energetic collisions is correctly oriented

Q25

Which statement about collision theory and the Arrhenius equation is correct?

Given

Comparison of the two treatments

Asked

The correct statement

Concept

The two share the energy factor, which is why they can be matched term by term.

Formula

Rate = P·Z·e^(−Ea/RT) versus k = A·e^(−Ea/RT)

Baby steps
  1. Both expressions contain the same exponential factor e^(−Ea/RT).
  2. Both therefore involve activation energy and temperature.
  3. Because they share that factor, comparing them identifies A with the collision frequency.
  4. Collision theory supplements the Arrhenius picture with a physical mechanism; it does not contradict it.

Answer · (a) Both contain the factor e^(−Ea/RT)

Q26

The proper orientation of reactant molecules leads to:

Given

Effect of proper orientation

Asked

The outcome

Concept

Correct geometry allows the bond-breaking and bond-making to proceed.

Formula

—

Baby steps
  1. NCERT states that proper orientation of reactant molecules leads to bond formation.
  2. Improper orientation makes them simply bounce back with no products formed.
  3. Orientation affects only whether a given collision succeeds, not Ea, Z or ΔH.
  4. So the correct answer concerns product formation.

Answer · (a) bond formation and product formation

Q27

For the reaction 2HI(g) → H₂(g) + I₂(g) with Ea = 209.5 kJ mol⁻¹ at 581 K, the fraction of molecules able to react is about 1.47 × 10⁻¹⁹. This tells you that:

Given

f = e^(−Ea/RT) ≈ 1.47 × 10⁻¹⁹

Asked

Interpretation

Concept

An enormous barrier makes the energy filter extremely severe.

Formula

f = e^(−Ea/RT)

Baby steps
  1. The fraction with enough energy is about one in 10¹⁹.
  2. So essentially every collision fails the energy test.
  3. The reaction still proceeds, because the collision frequency is itself enormous — of the order of 10³⁰ collisions per second per unit volume.
  4. The number quoted is the energy fraction, not the steric factor, so option (c) is wrong.

Answer · (a) the vast majority of collisions are energetically fruitless

Shortcut · Tiny energy fractions are normal. The rate survives because Z is astronomically large.
Q28

Which is the correct sequence of filters applied to collisions in collision theory?

Given

Structure of collision theory

Asked

The correct sequence

Concept

Two independent filters are applied to the total collision count.

Formula

Rate = Z × e^(−Ea/RT) × P

Baby steps
  1. Start from Z, the total number of collisions.
  2. Apply the energy filter e^(−Ea/RT) to get the energetic subset.
  3. Apply the orientation filter P to that subset.
  4. What survives both filters is the set of effective collisions, which produce products.

Answer · (a) All collisions → energetic enough → correctly oriented → effective

Q29

NCERT notes that you will study more advanced treatments of reaction rates in higher classes. The theory that replaces the hard-sphere picture is:

Given

Gap content — successor theories

Asked

The more advanced treatment

Concept

Transition state theory treats the activated complex properly rather than as colliding spheres.

Formula

—

Baby steps
  1. Collision theory's weakness is its hard-sphere assumption.
  2. Transition state theory, also called activated complex theory, models the complex at the barrier top explicitly.
  3. It accounts for molecular structure and internal motions that collision theory ignores.
  4. NCERT mentions that details of other theories come in higher classes.

Answer · (a) transition state (activated complex) theory