3.2.5
Intuition Badi picture (YE subtopic kyun exist karta hai)Nitrogen Group 15 ka gateway element hai. Ye atmosphere ka 78% almost inert N 2 reactive nitrogen (NH₃, HNO₃, nitrates) chahiye. Ye subtopic is baat ki kahaani hai ki hum inert N₂ ko kaise kabu karte hain (Haber), phir NH₃ ko stepwise oxidise karke HNO₃ banate hain (Ostwald), aur kaise nitrogen ke kai oxidation states (−3 se +5) oxides ka ek pura zoo de dete hain. Neeche jo bhi hai wo ek fact se nikalta hai : N ek bahut strong triple bond banata hai aur N–N single bonds weak hote hain.
N 2 : N ≡ N : triple bond = ek σ π σ 2 s σ 2 s ∗ π 2 p x = π 2 p y σ 2 p z = 2 10 − 4 === 3 ==
Common mistake Steel-man: "N₂ inert hai kyunki ye noble-gas-jaisa full octet hai."Ye sahi kyun lagta hai: har N ka octet complete hai, "satisfied" lagta hai. Fix: O₂ mein bhi full octets hain lekin wo reactive hai! Asli wajah 941 kJ/mol triple bond se aane wali kinetic barrier hai, octet nahi. Yahan inertness kinetic hai, thermodynamic nahi.
N 2 ( g ) + 3 H 2 ( g ) ⇌ 2 N H 3 ( g ) Δ H = − 92 kJ/mol gas moles kam hain (4 → 2).
Intuition Conditions kaise choose karein (Le Chatelier + kinetics ki ladai!)
Exothermic ⇒ low T zyada NH₃ favour karta hai (equilibrium ke hisaab se). Lekin low T ⇒ reaction bahut slow ho jaati hai. Compromise ≈ 700 K plus catalyst.Product side par gas moles kam ⇒ high pressure equilibrium ko right push karta hai. ≈ 200 atm use karo.Catalyst: finely divided Fe with K 2 O A l 2 O 3 faster reach karata hai, isse shift nahi karta .
Worked example Forecast-then-Verify: T badhaoForecast: exothermic reaction par T badhana. Verify: equilibrium left shift karta hai (kam NH₃), lekin rate badhti hai. Yield ↓ lekin equilibrium jaldi milta hai. Industry T ko dono balance karne ke liye choose karti hai. ✔
Hum pehle se NH₃ banate hain (N at −3). HNO₃ (N at +5 ) tak pahunchne ke liye hum nitrogen ko stages mein oxidise karte hain: − 3 → + 2 → + 4 → + 5
Common mistake Steel-man: "Step 3 sirf HNO₃ deta hai."Ye sahi kyun lagta hai: water + acid oxide → acid, clean lagta hai. Fix: ye ek disproportionation hai — ek NO₂ +5 tak jaata hai, doosra +2 (NO) tak neeche aata hai. NO ko recycle karna hi padega , warna apne nitrogen ka ek-tehai waste ho jaata hai.
Definition HNO₃ ki properties (oxidising acid)
Concentrated HNO₃ ek strong oxidiser hai: dilute form metals ke saath react karke mostly NO deta hai, concentrated form NO₂ deta hai.
Aqua regia = 3 HCl : 1 HNO₃ , Au aur Pt ko dissolve karta hai.N O 3 − brown ring test : [ F e ( H 2 O ) 5 N O ] 2 +
Definition Oxidation state ke hisaab se yaad karo
Oxide
N oxid. state
Name
Nature
N 2 O +1
nitrous oxide (laughing gas)
neutral
N O +2
nitric oxide
neutral, paramagnetic
N 2 O 3 +3
dinitrogen trioxide
acidic (H N O 2
N O 2 +4
nitrogen dioxide
acidic, paramagnetic, brown
N 2 O 4 +4
dinitrogen tetroxide
acidic (NO₂ dimer)
N 2 O 5 +5
dinitrogen pentoxide
acidic (H N O 3
Intuition NO aur NO₂ paramagnetic kyun hain; NO₂ dimerize kyun karta hai
N O odd electrons hain (11 valence e⁻) → ek unpaired → paramagnetic.N O 2 odd electron hai. Do NO₂ apne unpaired electrons pair karte hain aur ek N–N bond banate hain → N 2 O 4 2 N O 2 ( brown, paramagnetic ) ⇌ N 2 O 4 ( colourless, diamagnetic ) N 2 O 4
N 2 O 5 x 2 x + 5 ( − 2 ) = 0 Ye step kyun? Molecule neutral hai, O −2 hai.
2 x = 10 ⇒ x === + 5 ==
Recall N₂ exactly inert kyun hai? (3 reasons)941 kJ/mol triple bond (high activation energy), nonpolar/koi attack site nahi, bada HOMO–LUMO gap. Inertness kinetic hai.
Recall Haber conditions aur har ek ki wajah~200 atm (product gas moles kam hain), ~700 K (compromise — exothermic low T chahta hai lekin rate high T chahti hai), Fe catalyst + K₂O/Al₂O₃ promoters (equilibrium speed karta hai, shift nahi).
Recall Teen Ostwald steps oxidation states ke saath4 N H 3 + 5 O 2 → 4 N O + 6 H 2 O 2 N O + O 2 → 2 N O 2 3 N O 2 + H 2 O → 2 H N O 3 + N O
Recall Feynman: ek 12-saal ke bacche ko samjhaoHawaai mein nitrogen bhari hai, lekin ye ek couple ki tarah hai jo ek doosre ka haath itni kasas ke pakde hain (triple bond) ki wo kisi ke saath dance nahi karenge — yahi "inert" hai. Plant food (ammonia) banane ke liye hum unhe force se alag karte hain — zyada dabaav (pressure), thodi garmi, aur ek helper (iron catalyst) use karke. Phir hum dhire-dhire nitrogen ko oxygen pakadne dete hain, ek-ek step mein, jab tak wo strong acid (nitric acid) nahi ban jaata. Nitrogen oxygen ke kai "outfits" pehen sakta hai = alag-alag oxides.
Mnemonic Oxides ladder & OstwaldOxides: "1 2 3 4 4 5 " → N 2 O , N O , N 2 O 3 , N O 2 , N 2 O 4 , N 2 O 5 Ostwald chain: "A mmonia → NO → NO₂ → HNO₃ " = "Ammonia Naturally Nears Nitric" .
Haber: "HIGH P, low-ish T, Fe " = "Pressure Pushes, Heat Hurts, Iron Helps."
N2 molecule MO diagram — bond order & paramagnetism logicLe Chatelier Principle — Haber condition choices ko drive karta haiDisproportionation Reactions — Ostwald ka Step 3, paani mein NO₂Oxidation States and Redox — oxides mein N states assign karnaGroup 15 Hydrides PH3 vs NH3 — group mein neeche jaate trendsAqua regia and Noble Metals — HNO₃ + HCl chemistry
N₂ kinetically inert kyun hai? Bahut high triple-bond dissociation enthalpy (941 kJ/mol) → high activation energy; saath hi nonpolar hai, koi easy attack site nahi, aur bada HOMO–LUMO gap hai.
N₂ ka bond order? 3 (ek σ + do π); MO (10−4)/2 = 3.
3×(N–N single) vs N≡N enthalpy compare karo. 3×159 = 477 kJ/mol ≪ 941 kJ/mol, isliye triple bond bahut zyada favoured hai.
ΔH ke saath Haber equation. N₂ + 3H₂ ⇌ 2NH₃, ΔH = −92 kJ/mol.
Haber mein high pressure kyun help karta hai? 4 gas moles → 2; high P equilibrium ko kam moles (NH₃) ki taraf shift karta hai.
Haber ke liye ~700 K kyun, kam kyun nahi? Reaction exothermic hai isliye low T yield favour karta hai, lekin rate bahut slow ho jaati hai; ~700 K ek kinetic/equilibrium compromise hai.
Haber catalyst aur promoters? Finely divided Fe with K₂O aur Al₂O₃ promoters.
Kya catalyst NH₃ yield badhata hai? Nahi — ye dono directions mein equilibrium equally speed karta hai; yield (Kp) change nahi hoti.
Ostwald Step 1 (catalyst & equation)? 4NH₃ + 5O₂ →(Pt/Rh, 500 K) 4NO + 6H₂O; N: −3→+2.
Ostwald Step 2? 2NO + O₂ → 2NO₂; N: +2→+4.
Ostwald Step 3 aur iska type? 3NO₂ + H₂O → 2HNO₃ + NO; disproportionation (+4 → +5 aur +2); NO recycle hota hai.
Aqua regia ki composition? 3 parts conc. HCl : 1 part conc. HNO₃; Au, Pt ko dissolve karta hai.
Kaunse N oxides paramagnetic hain? NO aur NO₂ (odd number of electrons).
NO₂ N₂O₄ mein dimerize kyun karta hai? NO₂ mein ek unpaired electron hai; pairing se N–N bond banta hai jo diamagnetic N₂O₄ deta hai (low T/high P par favoured).
N₂O, NO, N₂O₃, NO₂, N₂O₅ mein N ka oxidation state? +1, +2, +3, +4, +5.
HNO₃ aur HNO₂ ka anhydride? N₂O₅ (HNO₃ ka), N₂O₃ (HNO₂ ka).
Brown ring test kya detect karta hai? Nitrate ion NO₃⁻; brown [Fe(H₂O)₅NO]²⁺ banta hai.
Fe catalyst, 200 atm, 700 K
Le Chatelier: low T + high P favour
oxidation states -3 to +5
