BharatNotes Why this chapter matters for UPSC: Chemical reactions are the foundation of industrial chemistry, environmental chemistry, and materials science — all GS3 staples. Corrosion costs India roughly 3.5% of GDP annually. The green hydrogen mission is built on electrolytic decomposition. Redox chemistry underpins smelting, the very basis of India's metals industry. Rancidity connects to food storage policy. Understanding reaction types lets you engage critically with fertilizer production, cement manufacturing, and battery technology questions.
PART 1 — Quick Reference Tables
Types of Chemical Reactions
| Type | General Form | Key Example | UPSC Angle |
|---|---|---|---|
| Combination | A + B → AB | CaO + H₂O → Ca(OH)₂ (slaked lime); Fe + O₂ → Fe₂O₃ | Cement setting; lime in agriculture |
| Decomposition — Thermal | AB → A + B (heat) | CaCO₃ → CaO + COâ‚‚ | Lime kiln / cement manufacturing; COâ‚‚ emissions |
| Decomposition — Photolytic | AB → A + B (light) | 2AgCl → 2Ag + Clâ‚‚ (sunlight) | Basis of photography; silver recovery |
| Decomposition — Electrolytic | AB → A + B (electricity) | 2Hâ‚‚O → 2Hâ‚‚ + Oâ‚‚ | Green hydrogen production |
| Displacement | A + BC → AC + B | Zn + CuSO₄ → ZnSO₄ + Cu | Reactivity series; metal extraction |
| Double Displacement | AB + CD → AD + CB | BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl | Precipitation; water treatment |
| Redox | Simultaneous oxidation + reduction | 2Fe + 3/2 O₂ → Fe₂O₃ (rusting) | Corrosion; smelting; bleaching |
| Exothermic | Products have less energy than reactants | Combustion, neutralisation, respiration | Energy release; fossil fuels |
| Endothermic | Products have more energy than reactants | Photosynthesis, evaporation, decomposition of CaCO₃ | Solar energy; industrial energy input |
Reactivity Series (Most → Least Reactive)
| Position | Metal | Key Property | Industrial Relevance |
|---|---|---|---|
| Most reactive | K, Na, Ca | React violently with water; cannot exist as free metal in nature | Stored under oil; used in coolants (Na in fast reactors) |
| Highly reactive | Mg, Al | React with hot water/steam; form stable oxides | Aluminium extraction requires electrolysis (energy-intensive) |
| Moderately reactive | Zn, Fe, Ni, Sn, Pb | React with dilute acids | Galvanisation (Zn); steel (Fe); solder (Sn+Pb) |
| Below hydrogen | Cu, Hg, Ag | Do not displace Hâ‚‚ from acids | Copper wiring; silver jewellery |
| Least reactive | Au, Pt | Occur as native metals; extremely stable | Native gold; platinum catalysts |
Corrosion: Types and Prevention
| Metal | Corrosion Product | Condition Required | Prevention Method |
|---|---|---|---|
| Iron | Feâ‚‚O₃·Hâ‚‚O (rust — hydrated iron oxide) | Both Oâ‚‚ and Hâ‚‚O needed | Galvanisation, painting, oiling, alloying (stainless steel), electroplating |
| Copper | CuCO₃·Cu(OH)â‚‚ (verdigris — green patina) | Oâ‚‚, COâ‚‚, moisture | Lacquering; tin plating |
| Silver | Agâ‚‚S (tarnish — black) | Hâ‚‚S in air | Silver polish; storage in airtight containers |
| Aluminium | Alâ‚‚O₃ (thin protective layer) | Oâ‚‚ | Self-passivating — oxide layer protects further corrosion |
PART 2 — Detailed Notes
1. What Is a Chemical Reaction?
A chemical reaction involves the rearrangement of atoms — bonds are broken and new bonds are formed. The substances that react are called reactants; the substances produced are called products.
How to identify a chemical reaction has occurred:
- Change in colour (copper sulphate + iron → iron sulphate turns light green)
- Evolution of gas (zinc + sulphuric acid → hydrogen gas)
- Formation of precipitate (lead nitrate + potassium iodide → yellow PbI₂ precipitate)
- Change in temperature (combustion releases heat; dissolving ammonium chloride absorbs heat)
- Emission of light (magnesium ribbon burns with a bright white flame)
Balancing equations follows the Law of Conservation of Mass (Lavoisier, 1789): total mass of reactants = total mass of products. Atoms are neither created nor destroyed in a chemical reaction.
2. Types of Reactions
Combination reactions involve two or more substances combining to form a single product. Most are exothermic. Example: quicklime (CaO) reacts vigorously with water releasing heat — this is the basis of cement setting and lime used in agriculture to neutralise acidic soils.
Decomposition reactions break a compound into simpler substances. They require energy input (heat, light, or electricity):
Thermal decomposition of limestone (CaCO₃ → CaO + COâ‚‚) is the first step in cement manufacturing. Every tonne of cement clinker produced releases ~0.6 tonnes of COâ‚‚ directly from this reaction — making cement one of the world’s largest industrial COâ‚‚ sources (~8% of global emissions). India is the 2nd largest cement producer globally.
[Additional] Green Cement — Reducing the Decomposition Penalty: Since the CO₂ from cement comes directly from the thermal decomposition of CaCO₃ (not just from burning fuel), switching to renewable energy alone cannot decarbonise cement. Three approaches reduce this “process emission”:
- Blended cements / SCMs (Supplementary Cementitious Materials): Partially replace clinker with industrial by-products — fly ash (from coal power plants), ground granulated blast furnace slag (GGBS from steel plants), and silica fume — which react with Ca(OH)₂ without requiring calcination. Reduces clinker factor and CO₂ by 20—40%.
- LC3 (Limestone Calcined Clay Cement): Uses calcined clay + limestone to replace 50% of clinker; CO₂ savings of ~40%; India has abundant clay deposits; large pilot projects underway (including housing projects that saved 80,000 tonnes CO₂ in 2024).
- Geopolymer cement: Uses fly ash or slag activated with alkali solutions — no limestone calcination needed; 75—90% lower CO₂ than Portland cement. Still at pre-commercial stage in India.
UPSC angle: India’s PAT (Perform Achieve Trade) scheme under BEE targets energy efficiency in cement; green cement is central to India’s hard-to-abate sector decarbonisation strategy under the LTS (Long-Term Strategy) submitted to UNFCCC.
UPSC GS3 — Green Hydrogen Mission: The electrolytic decomposition of water (2Hâ‚‚O → 2Hâ‚‚ + Oâ‚‚) is the core reaction behind green hydrogen. When powered by renewable electricity, no COâ‚‚ is emitted. India's National Green Hydrogen Mission (launched January 2023) targets 5 MMT (million metric tonnes) green hydrogen production per year by 2030, with an outlay of ₹19,744 crore. Key applications: fertiliser production (replacing grey hydrogen in Haber process), steel manufacturing (replacing coking coal), heavy transport.
Displacement reactions occur when a more reactive element displaces a less reactive one from its compound in solution. The reactivity series predicts whether a reaction will occur — a metal higher in the series will displace one lower. This principle is used in:
- Extraction of metals — more reactive metals reduce oxides of less reactive metals
- Galvanic cells (batteries) — voltage depends on the difference in reactivity between electrode metals
[Additional] Thermite Reaction — Welding Railway Tracks: Feâ‚‚O₃ + 2Al â†' 2Fe + Alâ‚‚O₃ + enormous heat (~3,000°C)
Aluminium (higher in reactivity series) displaces iron from iron oxide — an intensely exothermic displacement reaction. The molten iron produced flows into the gap between two rail ends and solidifies, creating a seamless joint. This thermite welding (Goldschmidt process) is the standard method used by Indian Railways to join rails, producing Long Welded Rail (LWR) track that eliminates clickety-clack joints and allows higher train speeds. No external power or electricity is needed — the chemical reaction itself provides ~3,000°C heat. Also used to repair heavy machinery and cracked metal structures on-site.
UPSC angle: Direct application of the reactivity series; appears in questions on Indian Railways infrastructure, high-speed rail corridor technology, and metallurgy.
Double displacement reactions involve the exchange of ions between two compounds. Precipitation reactions are a subtype — one product is insoluble and forms a solid precipitate. Important example: BaSOâ‚„ precipitate (white, insoluble) is used in medical barium meal X-rays to image the digestive tract.
3. Oxidation and Reduction (Redox Reactions)
Oxidation = loss of electrons (or gain of oxygen, or loss of hydrogen) Reduction = gain of electrons (or loss of oxygen, or gain of hydrogen) Mnemonic: OIL RIG — Oxidation Is Loss; Reduction Is Gain (of electrons) Oxidation and reduction always occur simultaneously — one substance is oxidised while another is reduced. The substance that causes oxidation is the oxidising agent (itself gets reduced); the substance causing reduction is the reducing agent (itself gets oxidised).
Corrosion is slow oxidation at the surface of metals. Rusting of iron requires both oxygen and water — neither alone causes rusting. The electrochemical mechanism involves iron acting as an anode (oxidised) while oxygen dissolved in water acts as a cathode (reduced), with water as the electrolyte.
UPSC GS3 — Economic cost of corrosion: India loses approximately ₹4—5 lakh crore annually to corrosion (estimated at ~3.5% of GDP) — comparable to what many countries spend on defence. This includes corrosion of infrastructure (bridges, pipelines, railways), industrial equipment, and vehicles. The Bureau of Indian Standards (BIS) and National Corrosion Council of India (NCCI) work on standards and awareness. Galvanised iron pipes (zinc-coated), stainless steel (18% Cr, 8% Ni), and cathodic protection systems (used on ships, underground pipelines) are key mitigation strategies.
[Additional] Cathodic Protection — How It Works: Cathodic protection exploits the reactivity series directly. A sacrificial anode (block of zinc or aluminium, which are more reactive than iron/steel) is bolted to a ship's hull or buried alongside an underground pipeline. Because zinc/aluminium are higher in the reactivity series, they preferentially oxidise (corrode) instead of the iron structure — the structure becomes the cathode, the sacrificial anode corrodes away and is periodically replaced. Used on: Indian Navy warships, merchant vessels, offshore oil platforms (ONGC), buried oil/gas pipelines (GAIL, IOC), bridge pilings in coastal areas. The same principle explains galvanisation — even if the zinc coating is scratched, zinc still protects the exposed iron underneath.
Smelting (extraction of metals from ores) is a large-scale reduction reaction. In the blast furnace, iron ore (Feâ‚‚O₃) is reduced by carbon monoxide (CO) — the reducing agent. Steel production — India is the world's 2nd largest producer — depends entirely on this redox chemistry.
Bleaching with chlorine gas exploits redox: Cl₂ + H₂O → HCl + [O] (nascent oxygen). This nascent oxygen oxidises the coloured compounds in cloth/paper, making them colourless. Sodium hypochlorite (NaOCl) in liquid bleach works the same way.
4. Exothermic and Endothermic Reactions
Exothermic reactions release energy (usually as heat and/or light):
- Combustion (coal, LPG, petrol, wood) — basis of thermal power, heating, transport
- Neutralisation reactions (acid + base → salt + water) — always exothermic
- Cellular respiration (glucose + O₂ → CO₂ + H₂O + ATP energy)
- Condensation (steam → water) and solidification
Endothermic reactions absorb energy from surroundings:
- Photosynthesis (requires solar energy to build glucose from COâ‚‚ + Hâ‚‚O)
- Evaporation (requires heat — basis of cooling towers, sweating)
- Decomposition reactions (require energy input — see above)
- Dissolving ammonium chloride (NHâ‚„Cl) in water (feels cold — used in instant cold packs)
Respiration is exothermic: Cellular respiration (Chapter 6) is the biological equivalent of combustion — glucose is "burned" with oxygen, releasing energy stored in ATP, plus heat and CO2. This is why your body temperature stays at ~37°C. The reaction: C₆Hâ‚â‚‚O₆ + 6Oâ‚‚ → 6COâ‚‚ + 6Hâ‚‚O + ~2870 kJ of energy per mole of glucose.
5. Rancidity
When fats and oils are oxidised by atmospheric oxygen, they develop an unpleasant smell and taste — this is called rancidity. It is a slow chemical change.
Prevention methods (relevant to food processing industry and FSSAI standards):
- Antioxidants: BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), Vitamin E (tocopherol), Vitamin C (ascorbic acid) are added to packaged foods — they get oxidised preferentially, protecting the fat
- Vacuum packaging: Removes oxygen
- Nitrogen flushing: Inert gas (Nâ‚‚) displaces oxygen in food packets (used for chips, biscuits, dry fruits)
- Refrigeration: Lower temperature slows the rate of oxidation
6. Industrial Chemistry Connections
| Process | Reaction Type | Product | Relevance |
|---|---|---|---|
| Haber Process | Combination (Nâ‚‚ + 3Hâ‚‚ → 2NH₃, 450°C, Fe catalyst) | Ammonia → fertilisers (urea, DAP) | India is world's 2nd largest fertiliser consumer |
| Contact Process | Catalytic oxidation (SO₂ → SO₃ → H₂SO₄) | Sulphuric acid | Most produced industrial chemical globally |
| Solvay Process | Multi-step; NaCl + NH₃ + CO₂ → NaHCO₃ → Na₂CO₃ | Soda ash, baking soda | Glass, detergent, paper industries |
| Cement manufacture | Thermal decomposition + combination | CaO → clinker | CO₂ emissions; construction industry |
| Chlor-alkali process | Electrolysis of NaCl(aq) → NaOH + Cl₂ + H₂ | Caustic soda, chlorine | Soap, paper, PVC, disinfectants |
[Additional] 1a. CCUS — Capturing the Unavoidable CO₂ from Cement and Industry
The chapter explains that thermal decomposition of limestone (CaCO₃ → CaO + CO₂) is an unavoidable source of CO₂ in cement manufacturing — the chapter already covers green cement (LC3, SCMs, geopolymer). What is missing is the next-level solution for the irreducible process emissions: Carbon Capture, Utilisation and Storage (CCUS) — which India has now formally committed to with a ₹20,000 crore Budget allocation.
CCUS Chemistry — Amine Scrubbing (Post-Combustion Capture): The most mature and widely deployed CO₂ capture technology uses monoethanolamine (MEA) — an organic amine — in a reversible acid-base reaction:
Absorption (absorber column, 40–60°C): CO₂ + 2 R-NH₂ (MEA) → R-NH₃⁺ + R-NHCOO⁻ (carbamate salt) Flue gas from cement kilns/power plants bubbles through aqueous MEA solution; CO₂ forms a water-soluble carbamate compound and is trapped; "clean" gas exits.
Regeneration (stripper, 110–120°C, steam heat): Heating reverses the reaction → concentrated pure CO₂ is released; "lean" MEA is recycled.
This is a reversible exothermic/endothermic reaction sequence — the very types of reactions this chapter defines. The CO₂ released from the stripper is compressed and either: (i) injected into deep geological formations (storage), (ii) used to produce fuels, chemicals, or construction materials (utilisation).
Alternative capture methods:
- Oxygen-enhanced calcination (oxy-fuel combustion): Kiln uses pure O₂ instead of air → flue gas is nearly pure CO₂ (no N₂ dilution) → easier to capture and compress (used in TB-1 at Ballabhgarh)
- Solid sorbent / Vacuum Swing Adsorption: CO₂ adsorbs onto solid amine or zeolite material under pressure; released under vacuum (used in TB-4)
- Carbon-negative mineralisation: CO₂ reacts with calcium/magnesium silicates → stable solid carbonates locked permanently (used in TB-2 at IIT Kanpur)
[Additional] India's CCUS Policy and Budget 2026-27 — GS3 (Climate / Science & Technology / Industry):
Policy timeline:
- December 2022: NITI Aayog released India's first "CCUS Policy Framework and its Deployment Mechanism" — establishing the foundational architecture
- December 2, 2025: DST launched India's first-ever R&D Roadmap to Enable Net Zero through CCUS (released by Prof. Ajay Kumar Sood, Principal Scientific Adviser to the Government of India); 3 phased pathways (2025-30: pilots; 2030-35: industrial integration; 2035-45: commercial scale); target: 750 million tonnes CO₂ captured from hard-to-abate sectors by 2050; DST established India's first three National Centres of Excellence in CCUS
- February 1, 2026 (Union Budget 2026-27): FM Nirmala Sitharaman announced ₹20,000 crore (~$2.2 billion) over 5 years for CCUS technologies — targeting 5 sectors: power, steel, cement, refineries, and chemicals
India's 5 CCU Cement Testbeds (National Technology Day, May 11, 2025): DST announced India's first cluster of CCU (Carbon Capture and Utilisation) pilots in cement industry — all academia-industry PPP models:
| Testbed | Academic Partner | Industry Partner | Technology |
|---|---|---|---|
| TB-1 | NCB Ballabhgarh (Haryana) | JK Cement | Oxy-fuel calcination; captures 2 tonnes CO₂/day; converts to lightweight concrete blocks and olefins |
| TB-2 | IIT Kanpur | JSW Cement | Carbon-negative mineralisation — locks CO₂ into solid minerals |
| TB-3 | IIT Bombay | Dalmia Cement | Catalyst-driven CO₂ capture at actual cement plant |
| TB-4 | CSIR-IIP + IIT Tirupati + IISc | JSW Cement | Vacuum Swing Adsorption integrated into construction materials |
| TB-5 | IIT Madras + BITS Pilani Goa | UltraTech Cement | Innovative carbon-lowering interventions |
Why CCUS is essential (beyond green cement): Even with LC3, geopolymer cement, and renewable energy, approximately 50–60% of cement's CO₂ is from the chemical decomposition of CaCO₃ — it is irreducible by energy switching alone. CCUS is the only technology that addresses this "process emission." Same logic applies to steel (blast furnace CO from iron ore reduction) and refineries — hence all five sectors in the Budget allocation.
UPSC synthesis: CCUS directly connects this chapter's thermal decomposition chemistry (cement) and redox reactions (steel) to India's Net Zero 2070 commitment, NDC 3.0 (submitted April 2026), Budget 2026-27 allocation, and the hard-to-abate sector decarbonisation challenge. The MEA amine scrubbing chemistry (reversible acid-base → exothermic absorption / endothermic regeneration) is a direct application of reaction types taught in this chapter.
[Additional] 1b. Sodium-Ion Batteries — When the Reactivity Series Chooses a Different Metal
The chapter covers the reactivity series and displacement reactions — the electrochemical foundation of all batteries (a more reactive metal in the series drives a higher cell voltage). The chapter mentions lithium-ion batteries implicitly through the green hydrogen/EV context. What is missing is the emerging shift to sodium-ion batteries — where India is developing indigenous technology specifically because of India's lithium import vulnerability.
Battery Electrochemistry — Why Reactivity Series Determines Battery Voltage: In any galvanic cell (battery), the cell voltage = the difference in standard reduction potentials between the two half-cell reactions:
| Metal/Ion | Standard Reduction Potential | Position in Reactivity Series |
|---|---|---|
| Li⁺/Li | −3.04 V | Among the most reactive (above Na) |
| Na⁺/Na | −2.71 V | Highly reactive (below Li, above Mg) |
| Mg²⁺/Mg | −2.37 V | Moderately reactive |
| Zn²⁺/Zn | −0.76 V | Moderately reactive |
| Cu²⁺/Cu | +0.34 V | Less reactive |
Because Li/Li⁺ has a more negative potential than Na/Na⁺, lithium-ion batteries achieve higher cell voltages (3.2–3.7 V) than sodium-ion (2.3–2.5 V) — a direct consequence of reactivity series position. Higher voltage → higher energy density per cell. This is why lithium dominated the first generation of EV batteries.
But sodium has key advantages: Sodium is ~1,000 times more abundant in Earth's crust (2.6% for Na vs ~0.0017% for Li); extractable from common salt (NaCl) and seawater; no geographic concentration risk; and at large manufacturing scale, sodium-ion cells are projected to be 20–40% cheaper than lithium-ion.
[Additional] Sodium-Ion Batteries — India's Lithium Problem and Indigenous Solution — GS3 (Science & Technology / Energy Security):
India's lithium import vulnerability:
- Geological Survey of India (GSI) discovered 5.9 million tonnes of inferred lithium resources at Salal-Haimana, Reasi district, Jammu & Kashmir (announced February 2023) — received significant media attention
- First auction (December 2023): FAILED — only 2 bids received, required minimum 3; scrapped
- Second auction (July 2024): FAILED AGAIN — zero bids; private companies who tested samples "were not satisfied with quantity and quality"
- India currently imports nearly all lithium from Australia, Chile, and Argentina — making EV battery supply chains import-dependent
Sodium-ion battery: performance vs lithium-ion:
| Parameter | Lithium-ion (LFP) | Sodium-ion (2025) |
|---|---|---|
| Cell voltage | 3.2–3.7 V | 2.3–2.5 V |
| Energy density | Up to 260 Wh/kg | 150–175 Wh/kg |
| Cycle life | 2,000–4,000 | Up to 10,000+ (CATL 2026) |
| Raw material | Lithium (scarce, imported) | Sodium (abundant, domestic) |
| Temperature range | Limited at −20°C | −40°C to 70°C viable |
India's sodium-ion battery ecosystem:
- KPIT Technologies, Pune (December 2023): Unveiled India's first indigenous sodium-ion battery technology — energy density 100–170 Wh/kg; 3,000–6,000 charge cycles; extreme temperature tolerance
- KPIT–Trentar deal (February 12, 2025): Technology transfer agreement with Trentar Energy Solutions for 3 GWh manufacturing capacity; applications: 2-wheelers, 3-wheelers, EVs, grid storage, UPS, marine, defence
- JNCASR (Bengaluru, DST institute — May 2025): Researchers developed a NASICON-type anode material (Na₁.₀V₀.₂₅Al₀.₂₅Nb₁.₅(PO₄)₃) — achieves 80% charge in 6 minutes, retention over 3,000+ cycles; breakthrough in fast-charging sodium-ion performance
- IISc Bengaluru: Researching mixed polyanionic cathode materials for next-generation sodium-ion batteries
- IIT Bombay (GESH): Published a roadmap for sodium-ion battery technology development in India
- ASPIRE Programme (UK-India bilateral, UK FCDO + India Ministry of Power + MNRE): Includes sodium-ion batteries as a priority technology for India's indigenous energy storage ecosystem
Global context (CATL, China):
- CATL Naxtra (launched April 2025): 175 Wh/kg sodium-ion battery for passenger cars; mass production from January 2026; Tianxing II (January 2026): first mass-produced sodium-ion commercial vehicle battery, 10,000+ cycles, operational at −40°C
- China's early lead in sodium-ion manufacturing is why India's indigenous development (KPIT, JNCASR, IISc) is strategically critical — to avoid replicating lithium's import dependency with sodium
UPSC synthesis: Sodium-ion batteries connect the reactivity series (this chapter) to energy security (GS3), Aatmanirbhar Bharat in advanced manufacturing (GS3), and India's EV and grid storage ambitions. KPIT's Dec 2023 indigenous battery + JNCASR's 2025 fast-charging breakthrough = India's answer to lithium import dependency. CATL's Naxtra 175 Wh/kg (2026) shows the global commercialisation milestone India is racing to match.
[Additional] 1b. Green Hydrogen via Electrolysis — National Green Hydrogen Mission
The chapter introduces the electrolysis of water as the textbook decomposition reaction (2H₂O → 2H₂ + O₂ with electric current). India's National Green Hydrogen Mission is exactly this NCERT reaction scaled to industrial level — using renewable-electricity-powered electrolysers to make hydrogen as an industrial feedstock and clean fuel.
Key Terms — Green Hydrogen:
| Term | Meaning |
|---|---|
| Green Hydrogen | H₂ produced by electrolysis of water using electricity from renewable energy sources (solar/wind); the only H₂ colour with zero direct CO₂ emissions |
| Grey Hydrogen | H₂ from steam methane reforming of natural gas (current dominant method); emits ~9 kg CO₂ per kg H₂; most of India's industrial H₂ today |
| Blue Hydrogen | Grey H₂ with Carbon Capture and Storage (CCS); lower emissions but not zero |
| Pink Hydrogen | H₂ from electrolysis using nuclear electricity |
| Electrolyser | The industrial device that splits water into H₂ + O₂ using DC electricity; types include Alkaline, PEM (Proton Exchange Membrane), and SOEC (Solid Oxide) |
| NGHM (National Green Hydrogen Mission) | India's flagship mission to make India a global hub for green H₂ production, use, and export; MNRE-administered |
| SIGHT | Strategic Interventions for Green Hydrogen Transition — the financial incentive scheme under NGHM (electrolyser manufacturing + green H₂ production) |
[Additional] National Green Hydrogen Mission — Decomposition Reaction at Industrial Scale (GS3 — Science and Technology / Energy):
NGHM key facts:
| Parameter | Detail |
|---|---|
| Cabinet approval | 4 January 2023 |
| Total outlay | ₹19,744 crore till FY 2029-30 |
| Implementing ministry | Ministry of New and Renewable Energy (MNRE) |
| Mission Director | Joint Secretary, MNRE |
| Target by 2030 | 5 MMT (Million Metric Tonnes) green H₂ production capacity per year |
| Associated RE addition | ~125 GW of renewable energy capacity by 2030 |
| Investment expected | ~₹8 lakh crore total investment (including industry); ~6 lakh jobs |
| Emission reduction | ~50 MMT CO₂-equivalent avoided annually by 2030 |
| Fossil import substitution | ~₹1 lakh crore worth of fossil fuel imports avoided |
SIGHT Programme — the financial incentive backbone:
| Component | Outlay | Purpose |
|---|---|---|
| Component I — Electrolyser manufacturing | ₹4,440 crore | PLI-style incentive for domestic electrolyser manufacturing |
| Component II — Green H₂ production | ₹13,050 crore | Production-linked incentive for green H₂ producers (FY 2025-26 to FY 2029-30) |
| SIGHT total | ₹17,490 crore | Largest component of NGHM |
Tender progress (as of May 2026):
| Tender | Date | Capacity awarded |
|---|---|---|
| Electrolyser Tranche I (SECI) | January 2024 | 1,500 MW/year awarded to 8 companies |
| Green H₂ production Tranche I (SECI) | January 2024 | 4.12 lakh tonnes/year awarded |
| Green H₂ production Tranche II (SECI) | March 2025 | 4.50 lakh tonnes/year additional |
| Cumulative as of May 2026 | ~8.62 lakh tonnes/year green H₂ + 1,500 MW electrolyser awarded |
Why electrolysis is preferred (linking back to Chapter 1):
| NCERT concept | Industrial application |
|---|---|
| Decomposition reaction | 2H₂O → 2H₂ + O₂ (the textbook reaction) |
| Electrolysis requires DC electricity | RE (solar/wind) generates DC after inverter — efficient pairing |
| Theoretical voltage | 1.23 V at standard conditions; practical ~1.8–2.0 V due to overpotential |
| Energy consumption | ~50–55 kWh per kg H₂ (state-of-the-art); efficiency improvements ongoing |
| Oxygen as by-product | Pure O₂ (1 kg H₂ → 8 kg O₂) — can be sold to industrial gas market |
Applications driving green H₂ demand:
| Sector | Use | India's existing demand |
|---|---|---|
| Fertiliser (urea) | Ammonia (NH₃) feedstock | ~3 MMT H₂/year (currently grey) |
| Petroleum refining | Hydrocracking, desulphurisation | ~3 MMT H₂/year |
| Steel | Direct Reduced Iron (DRI) — H₂ replaces coal | Future demand |
| Heavy transport | Fuel-cell trucks, buses, ships | Future demand |
| Total India H₂ demand | ~6 MMT/year (2025); projected ~12 MMT/year by 2030 |
UPSC synthesis: Key exam facts: NGHM approved 4 January 2023; outlay ₹19,744 crore till FY 2029-30; under Ministry of New and Renewable Energy (MNRE); target = 5 MMT green H₂ + 125 GW RE by 2030; SIGHT total ₹17,490 crore = ₹4,440 cr electrolyser + ₹13,050 cr production; 1,500 MW electrolyser + 8.62 lakh tonnes/year green H₂ awarded by May 2026; green H₂ = electrolysis of water using RE electricity (the NCERT Chapter 1 decomposition reaction). Prelims trap: NGHM is under MNRE (NOT MoEFCC, NOT Ministry of Power); green H₂ = renewable electrolysis (NOT nuclear — that is pink); blue H₂ = grey + CCS (NOT renewable); SIGHT outlay = ₹17,490 cr is part of the total ₹19,744 cr NGHM outlay (not separate); 5 MMT is the production target, 125 GW is the RE capacity target — different numbers, often confused.
Exam Strategy
Prelims traps:
- Rusting requires both oxygen and water — not just oxygen alone. Rusting does NOT occur in pure dry oxygen or pure water; it is an electrochemical process requiring both simultaneously.
- In electrolysis of water, hydrogen is liberated at the cathode (negative electrode) and oxygen at the anode (positive electrode) — not the other way around.
- Photolytic decomposition of silver chloride (AgCl) → Ag + Clâ‚‚ — the silver turns grey/black (metallic silver). This is why silver jewellery and silverware darkens in light.
- Oxidising agent itself gets reduced; reducing agent itself gets oxidised — exam questions frequently reverse this.
- The reactivity series lists metals in decreasing order of reactivity — potassium (K) at the top, platinum (Pt) at the bottom. A metal higher in the series displaces a metal lower in the series from its salt solution.
- Galvanisation protects iron by sacrificial protection — zinc, being more reactive than iron, oxidises first, protecting the iron even if the zinc coat is scratched.
Mains frameworks:
- Green hydrogen: electrolytic decomposition → renewable energy → National Green Hydrogen Mission → decarbonisation of fertiliser and steel → import substitution
- Corrosion costs: ₹4–5 lakh crore/year → infrastructure durability → bridge/pipeline safety → BIS standards
- Cement and climate: thermal decomposition of limestone → CO₂ emissions → Paris Agreement commitments → green cement alternatives
Practice Questions
Prelims:
With reference to the production of green hydrogen, which of the following is/are correct?
(a) Green hydrogen is produced by electrolysis of water using electricity from fossil fuels
(b) Green hydrogen production releases carbon dioxide as a by-product
(c) Green hydrogen is produced when renewable energy is used to electrolyse water
(d) Green hydrogen is produced by the Haber processThe process of galvanisation protects iron from rusting by coating it with:
(a) Tin
(b) Zinc
(c) Chromium
(d) Nickel
Mains:
What is green hydrogen? Discuss its potential as a clean fuel and the challenges in scaling up its production in India. (CSE Mains 2023, GS Paper 3, 15 marks)
Explain the major sources of SOâ‚‚ and NOâ‚“ emissions in India. How do these contribute to acid rain and what policy measures have been taken to control them? (CSE Mains 2019, GS Paper 3, 15 marks)
