Reaction of CO₂ with hot coke (carbon):
CO₂(g) + C(s) → 2CO(g)
Note: C is solid — it does NOT contribute to gas volume!
Let x dm³ of CO₂ react:
CO₂ remaining = (1 − x) dm³
CO formed = 2x dm³ (2 moles CO per mole CO₂, by Avogadro's law)
Total volume = (1 − x) + 2x = 1 + x dm³
Apply given condition:
1 + x = 1·4 → x = 0·4 dm³
CO₂ remaining = 1 − 0·4 = 0·6 dm³
CO formed = 2 × 0·4 = 0·8 dm³
CO₂(g) + C(s) → 2CO(g)
x = 0·4 dm³ reacted → 0·8 dm³ CO formed
CO₂ remaining = 0·6 dm³ | CO formed = 0·8 dm³
The reaction CO₂ + C → 2CO is called the Boudouard reaction. It is endothermic (ΔH > 0), so it proceeds forward at high temperatures. At low temperatures (~400°C), equilibrium favours CO₂. At high temperatures (~1000°C), equilibrium strongly favours CO. This reaction is industrially important in blast furnaces for iron production. Hot coke (carbon) reduces CO₂ to CO, which then reduces iron oxide (Fe₂O₃ → Fe). The reaction increases the number of moles of gas (1 mol CO₂ → 2 mol CO), so by Avogadro's law, volume increases at constant T and P.
Avogadro's law: at the same temperature and pressure, equal volumes of all gases contain equal numbers of molecules. Therefore, mole ratio = volume ratio for gases at same T and P. In this problem, CO₂(g) + C(s) → 2CO(g). At STP, 1 mole CO₂ occupies 22·4 L. If x dm³ of CO₂ reacts, it produces 2x dm³ of CO (volume doubles because 1 mol → 2 mol gas). Carbon is solid — it occupies no gas volume. Total gas volume = unreacted CO₂ + CO formed = (1−x) + 2x = 1+x.
📌 Colourless, odourless, highly toxic gas — binds Hb 200× stronger than O₂ (CO poisoning)
📌 Excellent reducing agent — reduces metal oxides at high temperature
📌 Burns with blue flame: 2CO + O₂ → 2CO₂
📌 Reacts with Cl₂ in presence of charcoal: CO + Cl₂ → COCl₂ (phosgene — war gas)
📌 Used in Mond process: Ni + 4CO → Ni(CO)₄ (nickel tetracarbonyl) — purification of nickel
📌 Bond order = 3 (triple bond: C≡O), similar to N₂
📌 Water gas: CO + H₂ (from C + H₂O at 1000°C)
📌 Producer gas: CO + N₂ (from C + air)
CO₂ is a linear molecule (O=C=O), non-polar despite having polar bonds (dipole moments cancel). It is a greenhouse gas — absorbs IR radiation from Earth's surface, contributing to global warming. Solid CO₂ is "dry ice" — sublimes at −78·5°C. CO₂ forms carbonic acid with water: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ (acidic). Uses: fire extinguisher (CO₂ blankets fire, cuts off O₂), carbonation of beverages, refrigerant (dry ice), photosynthesis (plant food), supercritical CO₂ as solvent.
📌 Diamond: sp³ hybridised, tetrahedral 3D network, hardest natural substance, non-conductor of electricity (no free electrons), high melting point
📌 Graphite: sp² hybridised, layered hexagonal structure, soft (layers slide), good conductor (delocalised π electrons), used as lubricant, electrode, pencil lead
📌 Fullerene (C₆₀): Buckminsterfullerene — soccer ball shape, 20 hexagons + 12 pentagons, sp² hybridised, discovered 1985 (Nobel Prize 1996)
📌 Carbon nanotubes: cylindrical graphite sheets, extremely strong, excellent conductors
📌 Graphene: single layer of graphite, 2D material, Nobel Prize 2010
Iron is extracted from iron ore (Fe₂O₃) in a blast furnace. Key reactions: (1) C + O₂ → CO₂ (combustion of coke at bottom, 2000°C). (2) CO₂ + C → 2CO (Boudouard reaction in the middle zone). (3) Fe₂O₃ + 3CO → 2Fe + 3CO₂ (reduction of iron ore at top). (4) CaCO₃ → CaO + CO₂ (limestone decomposes). (5) CaO + SiO₂ → CaSiO₃ (slag formation — removes silica impurity). The CO produced in the Boudouard reaction is the actual reducing agent that reduces Fe₂O₃ to Fe.
At STP (Standard Temperature and Pressure — 0°C, 1 atm): 1 mole of any ideal gas occupies 22·4 L = 22·4 dm³. At NTP (Normal Temperature and Pressure — 25°C, 1 atm): 1 mole occupies 24·5 L. This difference (22·4 vs 24·5) is tested in NEET — always check which standard conditions are specified. Mole ratio from balanced equation directly equals volume ratio for gases (by Avogadro's law). Solids and liquids do not contribute to gas volumes in such calculations.
Greenhouse gases (CO₂, CH₄, N₂O, H₂O vapour, CFCs) absorb IR radiation re-emitted from Earth's surface and re-radiate it back, warming the atmosphere. CO₂ is the most significant anthropogenic (human-caused) greenhouse gas due to fossil fuel combustion. Global warming → climate change → melting glaciers, rising sea levels, extreme weather events. The sixth mass extinction is currently underway — largely due to human activities including habitat destruction, pollution, and climate change — a key biology topic in NEET 2026.