BharatNotes Why this chapter matters for UPSC: Understanding physical vs chemical changes is foundational for questions on pollution (combustion releasing CO₂/SO₂), climate change (carbon cycle), industrial processes (chemical reactions), waste management (biodegradable vs non-biodegradable), weathering of rocks (physical/chemical), and natural disasters.
PART 1 — Quick Reference Tables
| Feature | Physical Change | Chemical Change |
|---|---|---|
| New substance formed? | No | Yes |
| Reversible? | Usually yes | Usually no |
| Change in mass? | No | No (Law of Conservation of Mass) |
| Energy change? | Small | Often large |
| Examples | Melting ice, dissolving salt, cutting paper, stretching rubber | Burning wood, rusting iron, cooking food, photosynthesis |
| Indicators | Change in state/shape/size | Gas evolved, colour change, temperature change, precipitate formed |
| Type of Chemical Change | Examples | UPSC Link |
|---|---|---|
| Combustion | Burning wood, petrol, coal | Air pollution, greenhouse gases, energy policy |
| Oxidation | Rusting of iron, burning magnesium | Metal corrosion (Chapter 4), air quality |
| Decomposition | Rotting food, composting | Waste management, soil fertility |
| Displacement | Iron displacing copper from copper sulphate | Electroplating, chemical industry |
| Neutralisation | Acid + base → salt + water | Soil amendment, antacids, industrial effluents |
| Photosynthesis | CO₂ + H₂O → glucose + O₂ | Carbon cycle, climate change, biodiversity |
| Environmental Change | Type | Consequence |
|---|---|---|
| Burning fossil fuels | Chemical (combustion) | CO₂ → global warming; SO₂/NOₓ → acid rain |
| Weathering of rocks | Physical (mechanical) + Chemical | Soil formation, landscape change |
| Glacial melting | Physical (state change) | Sea level rise, freshwater scarcity |
| Forest fire | Chemical (combustion) | Biodiversity loss, carbon release, air pollution |
| Composting | Chemical (decomposition) | Organic waste recycling, soil enrichment |
PART 2 — Detailed Notes
Physical Change: A change in which no new substance is formed. Only the physical properties (shape, size, state, colour) change. The composition of the substance remains the same. Most physical changes are reversible.
- Examples: Melting of ice (solid → liquid), boiling of water (liquid → gas), dissolving sugar in water, cutting paper, bending a wire, stretching rubber band
Chemical Change: A change in which one or more new substances with different properties are formed. Chemical bonds are broken and new bonds are formed. Usually irreversible.
- Examples: Burning of wood or paper, rusting of iron, ripening of fruit, curdling of milk, cooking an egg, photosynthesis, digestion of food
Indicators of Chemical Change:
- Evolution of gas (e.g., CO₂ from baking soda + vinegar)
- Change of colour (e.g., iron turning red-brown when it rusts)
- Change in temperature (exothermic: burning; endothermic: dissolving ammonium nitrate)
- Formation of precipitate (e.g., white precipitate when CO₂ is passed through lime water)
- Change in smell (e.g., food rotting)
Combustion: A chemical reaction between a substance and oxygen that produces heat and light. Combustion of carbon fuels (wood, coal, petrol, gas) produces carbon dioxide (CO₂) and water.
Law of Conservation of Mass: In a chemical reaction, the total mass of reactants equals the total mass of products. Matter is neither created nor destroyed.
Combustion and Climate Change
The burning of fossil fuels (coal, oil, natural gas) is the primary driver of anthropogenic (human-caused) climate change. When carbon-based fuels combust:
- CH₄ (methane) + 2O₂ → CO₂ + 2H₂O (complete combustion)
- Incomplete combustion produces CO (carbon monoxide) — toxic, odourless gas
India's Climate Commitments:
- NDC 2.0 (2022, 2030 targets): Net Zero by 2070; 45% reduction in emissions intensity of GDP by 2030 (from 2005 level); 50% non-fossil electricity capacity by 2030 (already achieved: 52.57% as of Feb 2026)
- NDC 3.0 (Cabinet approved 25 March 2026, 2035 targets): 47% emissions intensity reduction; 60% non-fossil capacity; carbon sink 3.5–4 billion tonnes CO₂-eq
Waste Management — Chemical vs Physical Processes:
- Biodegradable waste decomposes by chemical/biological processes → composting (Swachh Bharat Mission promotes composting)
- Non-biodegradable waste (plastics, glass) only undergoes physical changes → requires recycling
- Plastic pyrolysis: Converting waste plastic into fuel through thermal decomposition — currently being piloted under Swachh Bharat Mission 2.0
Weathering and Soil Formation:
- Physical weathering: Expansion/contraction due to temperature change, freeze-thaw cycles — breaks rocks mechanically
- Chemical weathering: Acid rain, carbonation (CO₂ + water → carbonic acid attacks limestone), oxidation — changes mineral composition
- Weathering creates regolith → further biological processes create soil
- India's Soil and Land Use Survey of India (SLUSI) monitors soil erosion — linked to changes in land use
Reversibility — The UPSC Nuance
While most physical changes are reversible and most chemical changes are irreversible, there are important exceptions:
- Dissolving salt: Physical change — reversible by evaporation
- Melting: Physical change — reversible by freezing
- Fermentation of glucose → alcohol + CO₂: Chemical change — irreversible
- Electrolysis of water → H₂ + O₂: Chemical change — but electricity can be used to reverse it (in fuel cells, H₂ + O₂ → water + electricity)
Carbon Cycle — Connecting Physical and Chemical Changes: The carbon cycle involves both physical and chemical changes:
- CO₂ dissolving in ocean water: physical absorption + chemical reaction (forms carbonic acid → bicarbonate ions)
- Photosynthesis: chemical change (CO₂ → glucose)
- Respiration: chemical change (glucose + O₂ → CO₂ + H₂O + energy)
- Combustion of fossil fuels: chemical change releasing stored ancient carbon Ocean acidification (pH falling due to CO₂ absorption) threatens coral reefs and marine biodiversity — a direct UPSC environment topic.
Testing for CO₂ — Lab Application: Carbon dioxide turns lime water (Ca(OH)₂) milky because: CO₂ + Ca(OH)₂ → CaCO₃ (white precipitate) + H₂O This is used as a standard test for CO₂ in laboratories and connects chemistry with environmental monitoring.
Forest Fires in India: Forest fires are chemical changes (combustion of biomass). India loses significant forest cover to fires annually:
- Uttarakhand, Himachal Pradesh, Odisha, Chhattisgarh are most fire-prone states
- ISFR (India State of Forest Report) by Forest Survey of India tracks forest fire alerts
- Forest fires release stored carbon, PM2.5, and toxic gases — connecting to air quality policy
[Additional] 5a. India's NDC 3.0 — The Full 2035 Climate Targets
The chapter references NDC 3.0 (Cabinet approved 25 March 2026) with brief targets. What is missing is the complete picture: how NDC 3.0 builds on NDC 2.0, what is genuinely new, India's already-achieved progress, and the UNFCCC submission details — all of which are high-frequency UPSC targets.
NDC (Nationally Determined Contribution): A country's self-determined climate action plan submitted to the UNFCCC under the Paris Agreement. Every 5 years, countries must submit updated, progressively more ambitious NDCs (the "ratchet mechanism" under Article 4.9 of the Paris Agreement).
India's NDC timeline:
- INDC (2015): India's first climate pledge, submitted before Paris Agreement was adopted
- NDC 1.0 (2016): Ratification of Paris Agreement
- NDC 2.0 (August 2022): Updated 2030 targets — 45% emissions intensity cut, 50% non-fossil capacity, 2.5-3.0 Gt carbon sink
- NDC 3.0 (April 2026): Updated 2035 targets — submitted to UNFCCC (UNFCCC Document Reference: unfccc.int/documents/611411)
Key terms:
| Term | Meaning |
|---|---|
| Emissions intensity | GHG emissions per unit of GDP — India uses this (not absolute emissions) as its NDC metric, reflecting its development status |
| Non-fossil installed capacity | % of total electricity generation capacity from non-fossil sources (solar, wind, hydro, nuclear) |
| Carbon sink | Forests and vegetation that absorb CO₂; measured in billion tonnes of CO₂-equivalent |
| Net Zero 2070 | India's target to achieve net-zero GHG emissions by 2070 — later than developed countries (EU 2050, USA 2050) under CBDR-RC principle |
[Additional] India's NDC 3.0 — Full 2035 Targets and What Is New (GS3 — Environment / Climate Policy):
Cabinet approval: 25 March 2026; formally submitted to UNFCCC: April 2026
NDC 2.0 vs NDC 3.0 — Comparison:
| Target | NDC 2.0 (by 2030) | NDC 3.0 (by 2035) |
|---|---|---|
| Emissions intensity reduction (vs 2005 baseline) | 45% | 47% |
| Non-fossil installed electricity capacity | 50% | 60% |
| Carbon sink (forest and tree cover) | 2.5–3.0 billion tonnes CO₂-eq | 3.5–4.0 billion tonnes CO₂-eq |
| Net Zero target | 2070 | 2070 (unchanged) |
Progress already achieved (as of February 2026):
- Non-fossil capacity: 52.57% — NDC 2.0 target of 50% by 2030 already surpassed 4 years early
- Emissions intensity: already reduced by 36% during 2005-2020 (progressing toward 45% by 2030)
- Carbon sink: already at 2.29 billion tonnes CO₂-eq (2021 data)
What is genuinely NEW in NDC 3.0 (beyond incremental number upgrades):
- Adaptation explicitly mainstreamed: First NDC to include specific adaptation actions — mangrove restoration (MISHTI scheme), Heat Action Plans across states, Glacial Lake Outburst Flood (GLOF) resilience in Himalayan states, climate-resilient coastal infrastructure
- LiFE (Lifestyle for Environment): First explicit NDC reference to PM Modi's LiFE movement — promoting individual-level consumption moderation as a climate tool; community campaigns like "Ek Ped Maa Ke Naam"
- Viksit Bharat framing: NDC 3.0 explicitly links climate action to India's 2047 Viksit Bharat vision — "climate-friendly and cleaner economic development pathways"
- Article 6.2 cooperation: NDC 3.0 explicitly references international carbon market cooperation under Article 6.2 of the Paris Agreement (bilateral carbon credit trading)
- Adaptation expenditure cited: India's adaptation-relevant expenditure rose from 3.7% of GDP (2015-16) to 5.60% of GDP (2021-22) — included to demonstrate domestic investment in climate resilience
UPSC synthesis: NDC 3.0 connects this chapter's combustion chemistry directly to India's highest-level climate policy. The chapter teaches: combustion of fossil fuels → CO₂ → greenhouse effect → warming. NDC 3.0 is India's formal commitment to reduce this. Key UPSC angles — (1) the NDC ratchet mechanism (why India submits every 5 years); (2) India uses emissions intensity targets (not absolute), reflecting CBDR-RC principle; (3) progress is ahead of schedule on non-fossil capacity (52.57% vs 50% target), but long-term Net Zero by 2070 is later than developed countries; (4) NDC 3.0 comparison table is a direct MCQ source. The 47% emissions intensity target and 60% non-fossil target for 2035 are the two key numbers.
[Additional] 5b. India's Carbon Credit Trading Scheme — Pricing Combustion Pollution
The chapter explains that combustion of fossil fuels releases CO₂ and causes climate change. What is missing is the economic policy mechanism for addressing this: carbon pricing through a domestic carbon market. India notified its Carbon Credit Trading Scheme (CCTS) in June 2023 — an intensity-based compliance carbon market that began mandatory compliance for seven industrial sectors from 1 April 2025. This is a major UPSC topic connecting chemistry (combustion → CO₂), economics (market-based environmental instruments), and governance (BEE, Ministry of Power).
Carbon Pricing — Core Concepts:
| Mechanism | How It Works | India Context |
|---|---|---|
| Carbon tax | Government sets a price per tonne of CO₂; emitters pay it | India has coal cess (National Clean Energy Fund) — indirect carbon price |
| Cap-and-trade | Government sets an absolute emissions cap; companies trade permits within the cap | EU ETS model; India's CCTS is NOT cap-and-trade — it is intensity-based |
| Intensity-based trading | Companies have a GHG intensity target (tCO₂ per unit output, not absolute emissions); trade certificates if they over- or under-perform | India's CCTS — allows industry to grow while cutting emission intensity |
| Carbon Credit Certificate (CCC) | India's tradeable instrument under CCTS — one CCC = one tonne of CO₂-equivalent emissions reduction | Issued by BEE; traded on power exchanges (IEX, PXIL) |
| Article 6.2 (Paris Agreement) | Bilateral carbon trading between countries: Internationally Transferred Mitigation Outcomes (ITMOs) | India-Japan JCM signed August 2025; India-South Korea deal operational |
PAT vs CCTS — the shift:
- PAT (Perform Achieve and Trade) scheme was India's previous energy efficiency trading scheme (2012): traded Energy Savings Certificates (ESCerts) based on Specific Energy Consumption (energy per unit output) — focused on energy efficiency, not GHG emissions
- CCTS replaces PAT progressively: measures GHG emissions intensity directly (tCO₂ per unit output); uses annual cycles (not 3-year); carries stronger financial penalties (2× average CCC price for non-compliance); verified by ISO 14064 standards
[Additional] India's Carbon Credit Trading Scheme (CCTS) — The Domestic Carbon Market (GS3 — Environment / Economy / Industry):
Legal foundation:
- Energy Conservation (Amendment) Act, 2022: Amended the Energy Conservation Act, 2001 to explicitly empower the government to establish a domestic carbon market
- CCTS notified: June 2023 (Ministry of Power, under BEE)
- First compliance year: FY 2025-26 (1 April 2025)
Governance:
- National Steering Committee for Indian Carbon Market (NSCICM): Apex body — co-chaired by Ministry of Power and MoEFCC
- Bureau of Energy Efficiency (BEE): Scheme administrator — sets GHG intensity targets, issues Carbon Credit Certificates (CCCs), manages the national carbon market registry
- Trading: CCCs traded on India Energy Exchange (IEX) and Power Exchange India Ltd. (PXIL) — first CCC trading expected mid-2026
- Verification: Annual verification by Accredited Carbon Verification Agencies (ACVAs) using ISO 14064 standards
Covered sectors (compliance from 1 April 2025 — FY 2025-26): Seven sectors entered compliance first:
- Aluminium
- Cement
- Chlor-Alkali
- Pulp and Paper
- Petroleum Refining
- Petrochemicals
- Textiles
Two sectors to be notified in subsequent phases: Fertiliser and Iron and Steel
Total: ~490–800 large industrial units will be covered under compliance obligations
How CCTS works:
- Each covered unit receives a GHG emission intensity target (tonnes CO₂-eq per unit of output)
- If actual emissions intensity is below target → unit generates surplus CCCs → can sell on exchange → earns revenue
- If actual emissions intensity is above target → unit must buy CCCs on exchange or surrender extra → financial penalty
- Non-compliance penalty: 2× average CCC market price
- One CCC = 1 tonne CO₂-equivalent emissions reduction
India's international carbon credits — Article 6.2:
- NDC 3.0 explicitly commits India to Article 6.2 cooperation — bilateral trading of Internationally Transferred Mitigation Outcomes (ITMOs)
- India-Japan Joint Crediting Mechanism (JCM): MoU signed 7 August 2025 (PIB) — India is Japan's 31st JCM partner country; eligible activities include renewable energy with storage, green hydrogen, sustainable aviation fuel (SAF), compressed biogas, ocean energy, green ammonia, carbon capture and storage (CCS)
- India-South Korea: Bilateral Article 6.2 Implementation Agreement — operational for FY 2025-26 collaboration on renewable energy and low-carbon technologies
- India-Singapore, India-UAE: Advanced-stage negotiations (early 2026)
- India's domestic carbon market projected to become the third largest carbon market in the world after China and the EU
UPSC synthesis: CCTS is the economic response to this chapter's core chemistry — combustion releases CO₂; carbon markets make emitters pay for that CO₂ financially. The policy chain is: combustion → GHG emissions → climate change (Chapter 5 chemistry) → UNFCCC/Paris Agreement → NDC commitments → carbon market (CCTS) → price signal → industry shifts to cleaner processes. UPSC GS3 questions test: difference between cap-and-trade (EU ETS) vs intensity-based (India CCTS); BEE's role in carbon markets; PAT vs CCTS evolution; Article 6.2 bilateral deals; India's carbon market as a governance innovation. Key facts: CCTS notified June 2023; Energy Conservation (Amendment) Act 2022 as legal basis; 7 sectors in compliance from April 2025; BEE as administrator; India-Japan JCM signed August 2025.
Exam Strategy
- The key distinction: physical change = no new substance; chemical change = new substance formed. When in doubt, ask: "Is the chemical composition different after the change?"
- Dissolving salt in water is a physical change (you can recover salt by evaporation). Do not confuse with chemical change.
- Cooking food is a chemical change — proteins denature, new compounds form. You cannot uncook a boiled egg.
- Law of Conservation of Mass: Matter is not created or destroyed in chemical reactions. Total mass before = total mass after. This is a basic Prelims science fact.
- Combustion of fossil fuels → CO₂ → greenhouse effect → global warming → climate change. This chain connects Chapter 5 with India's climate policy, NDCs, Paris Agreement.
- Acid rain is caused by SO₂ and NOₓ from combustion → chemical change (reaction with water vapour → H₂SO₄, HNO₃ → acid rain). Connects Chapters 2 and 5.
- Prelims trap: Complete combustion → CO₂ + H₂O. Incomplete combustion → CO (carbon monoxide) + soot. Both are chemical changes.
Practice Questions
Q1. Which of the following is a chemical change?
(a) Melting of ice
(b) Dissolving common salt in water
(c) Burning of wood
(d) Cutting of cloth
(c) Burning of wood
Q2. Consider the following statements:
- Carbon dioxide turns lime water milky.
- Combustion of fossil fuels is a physical change.
- Rusting of iron is an irreversible chemical change.
Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
(b) 1 and 3 only
Q3. The process of weathering of rocks involves:
(a) Only physical changes
(b) Only chemical changes
(c) Both physical and chemical changes
(d) Neither physical nor chemical changes — it is a biological process
(c) Both physical and chemical changes
