Which catalysis points are most asked in NEET previous-year papers?

NEET questions on catalysis usually test the enzyme for a given reaction such as zymase or invertase, optimum temperature and pH of enzymes, homogeneous versus heterogeneous examples, promoters and poisons in the Haber process, and the fact that a catalyst does not change the equilibrium constant.

Catalysis

ChemistrySurface ChemistryFor JEE aspirants

Catalysis is the speeding up of a chemical reaction by a substance, the catalyst, that is itself left chemically and quantitatively unchanged. A catalyst offers a new path with a lower activation energy, so it changes the rate but never $Δ H$ , $Δ G$ or the equilibrium constant. This page covers catalyst characteristics, promoters and poisons, homogeneous and heterogeneous catalysis, adsorption theory, selectivity, zeolites, enzymes and industrial catalysts. Catalysis is now a JEE Advanced-only topic (removed from JEE Main and NEET), though how a catalyst lowers $E_{a}$ is still asked in Chemical Kinetics.

On this page1What a catalyst does2Promoters and poisons3Homo vs hetero4How catalysts work5Activity and selectivity6Zeolites7Enzymes8Industry

Key Formulas - Quick Reference

★ Must learn A catalyst lowers $E_{a}$ of the forward and backward reactions equally: $Δ H$ , $Δ G$ , $K$ and the equilibrium composition are unchanged; equilibrium is only reached sooner.
★ Must learn Rate enhancement at the same $T$ (same $A$ ): $\frac{k _{c a t}}{k} = e^{(E_{a} - E_{a, c a t}) / R T}$ .
Same rate without the catalyst needs a higher temperature: $\frac{E _{a}}{T _{1}} = \frac{E _{a, c a t}}{T _{2}}$ (same $A$ ).
★ Must learn Homogeneous: catalyst in the same phase (NO in the lead chamber, $H^{+}$ in ester hydrolysis). Heterogeneous: different phase (Fe, Pt, Ni, $V_{2} O_{5}$ ).
★ Must learn Adsorption theory: diffusion → adsorption → surface reaction via an intermediate → desorption → diffusion away.
Selectivity: CO + $H_{2}$ gives $C H_{4}$ (Ni), $C H_{3} OH$ (Cu/ZnO- $C r_{2} O_{3}$ ), HCHO (Cu).
★ Must learn Enzymes: $E + S ⇌ ES \to E + P$ ; optimum $T$ 298-310 K, optimum pH 5-7.
Industry: Haber, Fe with Mo promoter (200 bar, 723-773 K); Contact, $V_{2} O_{5}$ (673-723 K); Ostwald, Pt-Rh gauze.

1. What a Catalyst Does

Potassium chlorate decomposes slowly when heated strongly, between 653 and 873 K. Add a little manganese dioxide and it decomposes faster, between 473 and 633 K. The $Mn O_{2}$ is recovered unchanged in mass and composition.

2KCl O_{3} Mn O_{2}, 473-633 K 2KCl + 3 O_{2}

Figure 1: A little

Mn O_{2}

lowers the decomposition range of

KCl O_{3}

by 180-240 K (from 653-873 K to 473-633 K) and speeds it up, yet is itself unchanged: that is catalysis.

Catalyst: a substance that alters the rate of a chemical reaction and remains chemically and quantitatively unchanged at the end. The phenomenon is catalysis. The term was introduced by Berzelius (1835).

Positive catalyst: speeds up a reaction (the usual meaning of the word).
Negative catalyst (inhibitor): slows a reaction. Glycerol slows the decomposition of $H_{2} O_{2}$ .
Autocatalysis: a product of the reaction catalyses it. In ester hydrolysis the acid formed supplies $H^{+}$ ions, and in the reaction of $KMn O_{4}$ with oxalic acid the $M n^{2 +}$ formed speeds it up. Such reactions start slowly and then accelerate.

2. Characteristics of Catalysts

Unchanged at the end in mass and chemical composition. Its physical form may change (lumps of $Mn O_{2}$ can end up as powder).
A small amount is enough. A trace of Pt, or one enzyme molecule per million substrate molecules, can do the job.
It cannot start an impossible reaction. A catalyst speeds up only reactions that are already feasible ( $Δ G < 0$ ).
It lowers the activation energy by opening a new path, usually through an intermediate. Forward and backward barriers fall by the same amount.
It does not change the equilibrium. $Δ H$ , $Δ G$ and $K$ are unchanged; equilibrium is reached sooner, with the same composition.
It is specific. A catalyst for one reaction may fail for another; the same reactants can give different products with different catalysts.

Figure 2: The catalyst offers a new path through an intermediate. Here

E_{a}

falls from 60 to 31 energy units (schematic), while reactants, products and

Δ H

stay the same, so

K

is unchanged.

Exam Trick A catalyst changes the road, not the start or the destination. Only the path and

E_{a}

change. Any option saying a catalyst changes

Δ H

Δ G

K

or the yield at equilibrium is wrong.

Key idea

A catalyst gives a lower-energy path: rate up, equilibrium unchanged.

3. Promoters and Poisons

Promoters are substances that increase the activity of a catalyst; poisons decrease or destroy it. In the Haber process, molybdenum is the promoter for the iron catalyst:

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

A poison is usually chemisorbed more strongly than the reactants, so it blocks the active sites. Carbon monoxide poisons iron in the Haber process, and $A s_{2} O_{3}$ poisons platinum in the contact process.

Figure 3: A poison is held more strongly than the reactants and blocks the active sites. CO poisons Fe in the Haber process, which is why CO from steam reforming is removed first. A promoter (Mo for Fe) does the opposite and raises activity.

Promoter

Raises the activity of a catalyst. Mo (with $K_{2} O$ , $A l_{2} O_{3}$ today) for Fe in the Haber process.

Poison

Lowers or destroys activity by blocking active sites. CO for Fe (Haber); $A s_{2} O_{3}$ for Pt (contact process).

Exam Trick Promoter Pumps, Poison Plugs. Mo pumps up Fe; CO plugs the Fe sites. Mo is not the catalyst in the Haber process: Fe is.

Quick Recall: tap to check

Does a catalyst change the equilibrium constant?

No. It lowers forward and backward

E_{a}

equally, so

K

Δ H

and

Δ G

stay the same.

Name the promoter and the catalyst in the Haber process.

Catalyst: finely divided Fe. Promoter: Mo.

What is autocatalysis? One example.

A product catalyses its own reaction, e.g.

M n^{2 +}

in the

KMn O_{4}

-oxalic acid reaction.

4. Homogeneous and Heterogeneous Catalysis

4.1 Homogeneous catalysis

Reactants and catalyst are in the same phase (all gases, or all in one solution).

2S O_{2} (g) + O_{2} (g) NO(g) 2S O_{3} (g)

Lead chamber process: $S O_{2}$ , $O_{2}$ and the catalyst NO are all gases.

C H_{3} COOC H_{3} (l) + H_{2} O (l) H^{+} (HCl) C H_{3} COOH (aq) + C H_{3} OH (aq)

C_{12} H_{22} O_{11} (aq) + H_{2} O (l) H^{+} (H_{2} S O_{4}) C_{6} H_{12} O_{6} (aq) + C_{6} H_{12} O_{6} (aq)

Hydrolysis of methyl acetate and inversion of cane sugar (giving glucose + fructose): everything is in solution.

4.2 Heterogeneous catalysis

Reactants and catalyst are in different phases, usually gases or liquids on a solid catalyst.

2S O_{2} (g) + O_{2} (g) Pt(s) 2S O_{3} (g)

N_{2} (g) + 3 H_{2} (g) Fe(s) 2N H_{3} (g)

4N H_{3} (g) + 5 O_{2} (g) Pt(s) 4NO (g) + 6 H_{2} O (g)

vegetable oil (l) + H_{2} (g) Ni(s) vegetable ghee (s)

Contact process, Haber process, Ostwald process and hydrogenation of oils. In the last one, one reactant is a liquid, one a gas and the catalyst a solid.

Figure 4: Homogeneous: catalyst and reactants in one phase (

H^{+}

in ester hydrolysis). Heterogeneous: catalyst in a different phase, and the reaction happens on its surface (solid Fe with gaseous

N_{2}

and

H_{2}

Homogeneous

One phase. Works through an intermediate compound. Examples: NO (lead chamber), $H^{+}$ (ester and sugar hydrolysis).

Heterogeneous

Different phases. Works by adsorption on the catalyst surface. Examples: Fe (Haber), Pt (Ostwald, contact), Ni (hydrogenation).

Key idea

Same phase = homogeneous; catalyst in a different phase = heterogeneous. A gas-phase catalyst like NO with gaseous reactants is still homogeneous.

5. How Catalysts Work

5.1 Intermediate compound formation (homogeneous)

The catalyst C first combines with a reactant to give an unstable intermediate, which then reacts with the second reactant and gives the catalyst back: A + C → AC; AC + B → AB + C. Each step has a lower barrier than the direct reaction. In the lead chamber process:

2NO (g) + O_{2} (g) 2N O_{2} (g)

N O_{2} (g) + S O_{2} (g) S O_{3} (g) + NO (g)

NO is regenerated, so a small amount keeps working.

5.2 Adsorption theory (heterogeneous)

The old adsorption theory said only that reactants concentrate on the catalyst surface, and the heat of adsorption helps the reaction. The modern adsorption theory combines this with intermediate compound formation. The surface of a solid, unlike its interior, has free valencies, which hold reactant molecules by loose chemical bonds. The mechanism has five steps:

Diffusion of reactants to the catalyst surface.
Adsorption of reactant molecules on the surface.
Chemical reaction on the surface through an adsorbed intermediate.
Desorption of products, which frees the surface for more reaction.
Diffusion of products away from the surface.

Figure 5: Diffusion, adsorption, surface reaction via an intermediate, desorption and diffusion away. The surface is freed at the end, so the catalyst is unchanged in mass and composition and a little of it works again and again.

Explains: why the catalyst is unchanged at the end; why a little catalyst is enough; why finely divided or rough catalysts (more free valencies) work better.
Does not explain: the action of promoters and poisons in full.

Key idea

Homogeneous catalysts work through an intermediate compound; solid catalysts work by adsorption, surface reaction and desorption.

6. Activity and Selectivity of Solid Catalysts

6.1 Activity

Activity is the ability of a catalyst to speed up a reaction, and it depends largely on the strength of chemisorption. Reactants must be held strongly enough to react, but not so strongly that they block the surface. For hydrogenation, activity increases from group 5 metals towards group 11, with the maximum at groups 7-9. Platinum is active enough to make hydrogen and oxygen combine:

2 H_{2} (g) + O_{2} (g) Pt 2 H_{2} O (l)

Figure 6: Activity depends on the strength of chemisorption: moderate is best. For hydrogenation, activity is highest for groups 7-9 (schematic trend).

6.2 Selectivity

Selectivity is the ability of a catalyst to direct a reaction to one product when several are possible. Starting from the same CO and $H_{2}$ , three catalysts give three different products:

Figure 7: Selectivity. From CO and

H_{2}

: Ni gives

C H_{4}

, Cu/ZnO-

C r_{2} O_{3}

gives

C H_{3} OH

, Cu gives HCHO. Each catalyst directs the reaction to one product.

So a substance that catalyses one reaction may fail to catalyse another: catalyst action is highly selective.

7. Shape-Selective Catalysis by Zeolites

Shape-selective catalysis is catalysis that depends on the pore structure of the catalyst and on the size of reactant and product molecules. Zeolites are microporous aluminosilicates: a three-dimensional silicate network in which some Si atoms are replaced by Al, giving an Al-O-Si framework with a honeycomb-like structure. Only molecules that fit the pores and cavities can react.

Figure 8: Shape-selective catalysis. Only molecules that fit the micropores of the zeolite can enter and react, so the pore size and shape pick the reactant and the product.

Zeolites occur naturally and are also synthesised for catalytic selectivity.
Used widely in petrochemical industries for cracking and isomerisation of hydrocarbons.
ZSM-5 converts alcohols directly into gasoline (petrol) by dehydrating them to a mixture of hydrocarbons.

Quick Recall: tap to check

What decides the activity of a solid catalyst?

The strength of chemisorption: moderate is best.

CO +

H_{2}

over Cu gives?

HCHO (methanal). Over Ni:

C H_{4}

H_{2} O

; over Cu/ZnO-

C r_{2} O_{3}

C H_{3} OH

Name a shape-selective catalyst and one use.

ZSM-5 (a zeolite): converts alcohols into gasoline.

8. Enzyme Catalysis

Enzymes are complex nitrogenous organic compounds made by living cells. They are proteins of high molar mass and form colloidal solutions in water. They catalyse the reactions of living systems, so they are called biochemical catalysts and the process biochemical catalysis. Many have been crystallised, and the first enzyme was synthesised in the laboratory in 1969.

8.1 Important enzyme reactions

C_{12} H_{22} O_{11} (aq) + H_{2} O (l) Invertase C_{6} H_{12} O_{6} (aq) + C_{6} H_{12} O_{6} (aq)

Cane sugar → glucose + fructose.

C_{6} H_{12} O_{6} (aq) Zymase 2 C_{2} H_{5} OH (aq) + 2C O_{2} (g)

2 (C_{6} H_{10} O_{5}) n (aq) + n H_{2} O (l) Diastase n C_{12} H_{22} O_{11} (aq)

C_{12} H_{22} O_{11} (aq) + H_{2} O (l) Maltase 2 C_{6} H_{12} O_{6} (aq)

N H_{2} CON H_{2} (aq) + H_{2} O (l) Urease 2N H_{3} (g) + C O_{2} (g)

Enzyme	Source	Reaction
Invertase	yeast	sucrose → glucose + fructose
Zymase	yeast	glucose → ethyl alcohol + $C O_{2}$
Diastase	malt	starch → maltose
Maltase	yeast	maltose → glucose
Urease	soyabean	urea → $N H_{3}$ + $C O_{2}$
Pepsin	stomach	proteins → peptides
Trypsin	pancreatic juice (intestine)	proteins → amino acids
Lactobacilli enzymes	bacteria in curd	milk → curd

8.2 Characteristics of enzyme catalysis

Most highly efficient: one enzyme molecule may transform about a million reactant molecules per minute.
Highly specific: each enzyme catalyses one reaction. Urease hydrolyses urea only, not any other amide.
Optimum temperature: activity is highest at 298-310 K and falls on either side. Body temperature (310 K) suits enzymes.
Optimum pH: activity is highest at pH 5-7.
Activators and co-enzymes increase activity. Co-enzymes are small non-protein molecules (often vitamins). Activators are metal ions such as $N a^{+}$ , $M n^{2 +}$ , $C o^{2 +}$ , $C u^{2 +}$ bound weakly to the enzyme; amylase is very active with NaCl ( $N a^{+}$ ).
Inhibitors and poisons bind to the active groups and reduce or destroy activity. Many drugs act as enzyme inhibitors.

Figure 9: Enzymes work best in a narrow window: optimum temperature 298-310 K (curve peaks at 310 K here, near body temperature) and optimum pH 5-7. Outside it the protein changes shape and activity falls.

The pH 5-7 range is the general rule. Some enzymes are exceptions: pepsin works in the acidic stomach (around pH 2).

8.3 Mechanism: lock and key

An enzyme particle has cavities of a characteristic shape on its surface, lined with active groups such as $- N H_{2}$ , $- COOH$ , $- SH$ and $- OH$ . These are the active sites. A substrate of complementary shape fits into the cavity like a key in a lock, forming an activated complex, which then breaks into products:

Binding of enzyme to substrate: $E + S \to E S^{‡}$
Decomposition of the activated complex: $E S^{‡} \to E + P$

Figure 10: Lock and key. The substrate fits the active site (step 1:

E + S \to E S^{‡}

, the activated complex), then the complex breaks into products (step 2:

E S^{‡} \to E + P

). The shape match is why each enzyme is so specific.

JEE Advanced Michaelis-Menten kinetics. Treating

E + S ⇌ ES \to E + P

with a steady state for ES gives the rate

v = \frac{V _{ma x} [ S ]}{K _{m} + [ S ]}

. At low [S] (

[S] ≪ K_{m}

v \approx \frac{V _{ma x}}{K _{m}} [S]

: first order in substrate. At high [S] (

[S] ≫ K_{m}

v \approx V_{ma x}

: zero order, because every active site is occupied. At

[S] = K_{m}

v = V_{ma x} /2

. This is why enzyme reactions show saturation, like the Langmuir isotherm.

Figure 11: Enzyme kinetics. First order in [S] at low [S], zero order at high [S] when all active sites are busy (saturation).

K_{m}

is the [S] that gives

V_{ma x} /2

Exam Trick Enzymes like the body. Optimum 298-310 K (body 310 K) and pH 5-7. And remember the sugar chain: diastase (starch → maltose), maltase (maltose → glucose), zymase (glucose → alcohol).

Key idea

Enzymes are protein catalysts: very efficient, very specific (lock and key), and fussy about temperature and pH.

9. Catalysts in Industry

Process	Reactions	Catalyst and conditions
Haber (ammonia)	$N_{2} + 3 H_{2} ⇌ 2N H_{3}$	finely divided Fe, Mo promoter; 200 bar, 723-773 K (now iron oxide with $K_{2} O$ and $A l_{2} O_{3}$ )
Ostwald (nitric acid)	$4N H_{3} + 5 O_{2} \to 4NO + 6 H_{2} O$ ; $2NO + O_{2} \to 2N O_{2}$ ; $4N O_{2} + 2 H_{2} O + O_{2} \to 4HN O_{3}$	Pt (platinum-rhodium gauze) for the first step
Contact (sulphuric acid)	$2S O_{2} + O_{2} ⇌ 2S O_{3}$ ; $S O_{3} + H_{2} S O_{4} \to H_{2} S_{2} O_{7}$ (oleum); $H_{2} S_{2} O_{7} + H_{2} O \to 2 H_{2} S O_{4}$	$V_{2} O_{5}$ (or platinised asbestos); 673-723 K
Lead chamber (sulphuric acid)	$2S O_{2} + O_{2} \to 2S O_{3}$	NO (gas): homogeneous
Hydrogenation of oils	vegetable oil + $H_{2}$ → vanaspati ghee	finely divided Ni
Deacon (chlorine)	$4HCl + O_{2} \to 2C l_{2} + 2 H_{2} O$	$CuC l_{2}$

9.1 Classifying any catalysed reaction

Figure 12: Classify any catalysed reaction in three questions: enzyme? same phase? pore-controlled? Then look for promoters and poisons.

Quick Recall: tap to check

Optimum temperature and pH for most enzymes?

298-310 K and pH 5-7.

Which enzyme converts starch into maltose?

Diastase (from malt).

Catalyst in the contact process today, and why not Pt?

V_{2} O_{5}

; Pt is costly and is poisoned by

A s_{2} O_{3}

9.2 The whole concept at a glance

Figure 13: The whole concept on one page. Revise from the centre outwards.

10. Solved Examples

Solved Example 1

In the Haber process, hydrogen is obtained by reacting methane with steam in the presence of NiO (steam reforming). Why is it necessary to remove CO before the gases reach the ammonia converter? (NCERT Intext 5.4)

Solution:

C H_{4} (g) + H_{2} O (g) NiO CO (g) + 3 H_{2} (g)

CO is a poison for the iron catalyst. It is chemisorbed strongly on the Fe surface and blocks the active sites, so $N_{2}$ and $H_{2}$ cannot be adsorbed and the rate falls sharply.

Solved Example 2

Why is ester hydrolysis slow in the beginning and faster after some time? (NCERT Intext 5.5)

Solution:

C H_{3} COO C_{2} H_{5} + H_{2} O C H_{3} COOH + C_{2} H_{5} OH

The acetic acid formed ionises and supplies $H^{+}$ ions, which catalyse the hydrolysis. As more acid forms, the reaction speeds up. A reaction catalysed by its own product shows autocatalysis.

Solved Example 3

A catalyst lowers the activation energy of a reaction by 20 kJ mol

^{- 1}

at 300 K. By what factor does the rate increase, if the pre-exponential factor is unchanged? (

R = 8.314

J K

^{- 1}

mol

^{- 1}

)

Solution:

\frac{k _{c a t}}{k} = e^{Δ E_{a} / R T} = e^{20000/ (8.314 \times 300)} = e^{8.02} \approx 3.0 \times 1 0^{3}

The catalysed reaction is about 3000 times faster.

Solved Example 4

The activation energy of a reaction is 100 kJ mol

^{- 1}

without a catalyst and 75 kJ mol

^{- 1}

with it. The catalysed reaction runs at 300 K. At what temperature would the uncatalysed reaction have the same rate (same

A

Solution:

Equal rates need equal $e^{- E_{a} / R T}$ , so $\frac{E _{a}}{T _{1}} = \frac{E _{a, c a t}}{T _{2}}$ .

T_{1} = \frac{E _{a} \times T _{2}}{E _{a, c a t}} = \frac{100 \times 300}{75} = 400 K

Solved Example 5

A catalyst does not change:
(A) the activation energy
(B) the rate constant
(C) the equilibrium constant
(D) the mechanism

Solution:

Answer: (C). A catalyst lowers the forward and backward activation energies equally, so both rate constants rise by the same factor and $K = k_{f} / k_{b}$ is unchanged.

Solved Example 6

Which of these is an example of heterogeneous catalysis?
(A) NO in the lead chamber process
(B)

H_{2} S O_{4}

in the inversion of cane sugar
(C) Fe in the Haber process
(D) HCl in the hydrolysis of methyl acetate

Solution:

Answer: (C). Solid Fe with gaseous $N_{2}$ and $H_{2}$ is two phases. In (A) all are gases; in (B) and (D) all are in solution.

Solved Example 7

The enzyme that converts glucose into ethyl alcohol is
(A) invertase
(B) zymase
(C) diastase
(D) maltase

Solution:

Answer: (B). Zymase (from yeast) converts glucose into ethanol and $C O_{2}$ . Invertase acts on sucrose, diastase on starch, maltase on maltose.

Practice Questions

What is the role of desorption in catalysis? (NCERT Intext 5.6)Answer: It removes the products and frees the active sites for fresh reactant molecules, so the catalyst keeps working.
What role does adsorption play in heterogeneous catalysis?Answer: Reactants are adsorbed on the catalyst surface, which raises their concentration there, weakens their bonds and forms an intermediate; the heat of adsorption also helps.
What are enzymes? Write the mechanism of enzyme catalysis in brief.Answer: Protein biochemical catalysts. Lock and key: $E + S \to E S^{‡}$ , then $E S^{‡} \to E + P$ .
Give four examples of heterogeneous catalysis.Answer: Fe in the Haber process; Pt in the Ostwald process; Pt or $V_{2} O_{5}$ in the contact process; Ni in hydrogenation of oils.
What do you mean by activity and selectivity of catalysts?Answer: Activity: ability to speed up a reaction (depends on strength of chemisorption). Selectivity: ability to direct a reaction to one particular product.
Describe some features of catalysis by zeolites.Answer: Microporous aluminosilicates (Al-O-Si); honeycomb pores; shape-selective; used in cracking and isomerisation; ZSM-5 turns alcohols into gasoline.
What is shape-selective catalysis?Answer: Catalysis that depends on the pore structure of the catalyst and the size of reactant and product molecules, as in zeolites.
Name the product of CO and $H_{2}$ over Cu/ZnO- $C r_{2} O_{3}$ .Answer: Methanol: $CO + 2 H_{2} \to C H_{3} OH$ .

Common Mistakes to Avoid

Watch out

Saying a catalyst shifts the equilibrium or increases the yield. It only helps equilibrium arrive sooner.
Saying a catalyst lowers only the forward activation energy. Forward and backward barriers fall by the same amount.
Calling Mo the catalyst in the Haber process. Fe is the catalyst; Mo is the promoter.
Calling the lead chamber process heterogeneous. NO and the reactants are all gases: homogeneous.
Claiming a catalyst is unchanged in every way. It is unchanged in mass and chemical composition, but its physical form can change.
Believing a catalyst can make a non-spontaneous reaction ( $Δ G > 0$ ) happen. It only speeds up feasible reactions.
Writing pepsin: proteins → amino acids. Pepsin gives peptides; trypsin carries hydrolysis on to amino acids.
Mixing up the sugar enzymes: invertase (sucrose), diastase (starch), maltase (maltose), zymase (glucose to alcohol).

Frequently Asked Questions

What is catalysis in chemistry?

Catalysis is the change in the rate of a reaction caused by a substance, the catalyst, that remains chemically and quantitatively unchanged at the end. A catalyst provides an alternative path with lower activation energy. Manganese dioxide in the decomposition of potassium chlorate is a classic example.

Does a catalyst change the equilibrium constant?

No. A catalyst lowers the activation energy of the forward and backward reactions by the same amount, so both rate constants increase by the same factor. The equilibrium constant, enthalpy change, Gibbs energy change and equilibrium composition stay the same; equilibrium is simply reached sooner.

What is the difference between homogeneous and heterogeneous catalysis?

In homogeneous catalysis the catalyst and reactants are in the same phase, such as nitric oxide in the lead chamber process or H+ ions in ester hydrolysis. In heterogeneous catalysis they are in different phases, such as solid iron with nitrogen and hydrogen gases in the Haber process.

What are catalytic promoters and poisons?

Promoters increase the activity of a catalyst; molybdenum promotes iron in the Haber process. Poisons decrease or destroy activity, usually by being chemisorbed strongly on the active sites; carbon monoxide poisons iron in the Haber process and arsenic oxide poisons platinum in the contact process.

How does the adsorption theory explain heterogeneous catalysis?

Reactants diffuse to the catalyst surface and are adsorbed on its free valencies. They react on the surface through an intermediate, the products desorb and then diffuse away, freeing the sites again. This explains why the catalyst is unchanged and why finely divided catalysts work better.

Why are enzymes highly specific?

An enzyme has active sites whose shape matches only its own substrate, like a lock that fits one key. The substrate binds to form an enzyme-substrate complex, which breaks into products. A molecule of a different shape cannot fit, so urease, for example, hydrolyses only urea.

Is catalysis in the JEE Main and NEET syllabus?

Surface Chemistry, including homogeneous and heterogeneous catalysis, adsorption theory, zeolites and enzyme catalysis, has been removed from the JEE Main and NEET syllabi and is now tested only in JEE Advanced. The effect of a catalyst on activation energy and rate is still part of Chemical Kinetics in both exams.

How is catalysis tested in JEE?

JEE uses catalysis mainly through kinetics: a catalyst lowers activation energy, so the rate constant rises by the factor e to the power of the drop in activation energy divided by RT, while enthalpy and the equilibrium constant stay the same. Older JEE Main papers also asked about industrial catalysts, zeolites and enzyme conditions.

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