2.8.12
Ek catalyst ek matchmaker jaisa hai. Yeh nahi badalta ki reaction kahan khatam hoti hai (products, equilibrium) — yeh badalta hai ki wahan kitni jaldi pahuncha jaata hai. Yeh ek naya rasta banata hai energy ki hill ke upar se: ek aisa rasta jisme lower activation energy E a
Catalyst E a aur backward reaction dono ko equally fast karta hai → K e q
Yeh regenerate hota hai (consumed nahi hota).
Mechanism badal jaata hai — yahi ek reason hai ki E a
Definition Catalyst aur CatalysisCatalyst ek aisi substance hai jo reaction ki rate badhata hai ek alternative pathway provide karke jisme lower activation energy ho, aur reaction ke end mein regenerate ho jaata hai (chemically amount mein unchanged).
Catalysis = catalyst dwara rate change hone ki phenomenon.
Positive catalyst : E a Negative catalyst (inhibitor) : effective E a Promoter : catalyst ki activity badhata hai (e.g. Haber process mein Mo).Poison : catalyst ki activity destroy karta hai (e.g. Pt pe As).
Arrhenius equation se (neeche derive kiya hai), rate constant
k = A e − E a / R T . E a negative exponential mein baitha hai. Sirf 20 kJ/mol k hazaaron guna tak jump kar sakta hai. Woh exponential sensitivity hi reason hai ki thoda sa catalyst itna bada effect kyun deta hai.
Worked example Forecast-then-Verify: Kitna guna faster?Ek catalyst E a 75 50 kJ/mol T = 300 K Pehle forecast karo (padhne se pehle karo!): bada drop hai, expect karo ek huge number.
Compute karo. Δ E a = 25000 J/mol R T = 8.314 × 300 = 2494 J/mol k u n k c a t = e 25000/2494 = e 10.02 ≈ 2.2 × 1 0 4 . Yeh step kyun? Humne drop ko R T E a / R T ~22,000× faster sirf 25 kJ/mol cut se. Yahi hai exponential magic.
Definition Homogeneous catalysisCatalyst aur reactants same phase HOW kaam karta hai: catalyst ek soluble intermediate banata hai jo aage react karta hai.
Examples:
Lead chamber process: 2 S O 2 + O 2 N O ( g ) 2 S O 3
Aqueous H + C H 3 C O O C 2 H 5 + H 2 O H + ( a q ) …
Definition Heterogeneous catalysisCatalyst reactants se different phase solid catalyst with gas/liquid reactants. Reaction surface pe hoti hai.
HOW (adsorption theory), step by step:
Reactant ka surface ki taraf Diffusion .
Active sites pe Adsorption (bonds stretch/weaken hote hain → yahi E a Adsorbed species ki Reaction .
Products ka Desorption (site free hoti hai → catalyst regenerate hota hai).
Examples: Haber (N 2 + 3 H 2 F e / M o 2 N H 3 2 S O 2 + O 2 V 2 O 5 2 S O 3 alkene N i alkane
Definition Enzyme catalysisEnzymes specific — ek enzyme, roughly ek reaction, active site pe lock-and-key fit ke through.
HOW: E + S ⇌ E S → E + P Traits: enormous rate boost (1 0 6 1 0 20
Common mistake "Catalyst equilibrium ko products ki taraf shift kar deta hai."Kyun sahi lagta hai: catalysts products zyada aur jaldi banane mein help karte hain, toh zaroor reaction ko "aage" le jaate hain.
Fix: catalyst E a dono directions ke liye same amount se girata hai. Kyunki K e q = k f / k b k K e q same equilibrium par pahuncho — bas jaldi . Thermodynamics (Δ G kinetics badlti hai.
Δ H Kyun sahi lagta hai: catalyst ke saath energy diagram neeche dikhta hai.
Fix: sirf peak (transition state) girta hai. Reactant aur product energy levels fixed hain, isliye Δ H = H p r o d − H r e a c t same rehta hai. Catalyst hill badalta hai, valleys nahi.
Common mistake "Zyada catalyst matlab hamesha proportionally faster, forever."Kyun sahi lagta hai: homogeneous catalysis mein rate often catalyst ke saath badhti hai.
Fix: heterogeneous/enzyme catalysis mein reaction surface active sites se limited hoti hai. Jab ek baar har site occupied ho jaaye, zyada substrate add karne se (ya crowding se) saturation milta hai — rate V ma x
Recall Feynman: ek 12-saal ke bacche ko explain karoImagine karo ki tumhe ek bhaari ball ek badi hill ke upar se roll karni hai apne dost ke ghar pahunchne ke liye. Yeh bahut mushkil hai — bahut kam balls pahunch paati hain. Ek catalyst ek aisa dost hai jo hill mein tunnel khodta hai: ek bahut aasaan rasta. Ab bahut zyada balls per minute pass ho jaati hain. Tunnel khodne wali khatam nahi hoti — woh agle ball ke liye ready hai. Aur notice karo: tumhara dost ka ghar same jagah par hai jaise pehle tha (same products, same "kitni door"), tum bas jaldi pahunch jaate ho. Enzymes super-clever tunnel-diggers hain jo sirf ek special shape ki ball ko jaane deti hain — jaise ek lock jo ek hi key se khulti hai.
Mnemonic Types aur rules yaad karo"Same room, Different room, Living room."
Homo geneous = Same phase (homo = same).Hetero geneous = Different phase (surface, solid).Enzyme = Living (biological), lock-and-key.
Aur catalyst kya karta hai iske liye: "Lower the HILL, not the HOUSE" — E a Δ H K e q
Recall Quick self-test (answers cover kar lo)
Catalyst kaunsi ek quantity change karta hai reaction speed karne ke liye? ==Activation energy E a
Kya yeh K e q Nahi — dono directions equally fast hoti hain
Contact process ka catalyst? ==V 2 O 5
Half V ma x [ S ] K M
Catalyst ko kya define karta hai? Ek substance jo reaction ko lower-E a
Catalyst K e q Yeh forward aur backward reactions dono ke liye E a k f k b K e q = k f / k b
Kya catalyst Δ H Nahi — sirf transition-state (peak) energy girti hai; reactant aur product energy levels fixed rehti hain.
Homogeneous vs heterogeneous catalysis? Homogeneous = catalyst aur reactants same phase mein; heterogeneous = catalyst different phase mein (usually solid surface with gas/liquid reactants).
Heterogeneous catalysis ke chaar surface steps? Diffusion → Adsorption on active sites → Reaction → Desorption of products.
Haber process mein catalyst (aur promoter)? Finely divided Fe; promoter hai Mo.
Contact process mein catalyst? V 2 O 5
Lead-chamber SO₂ oxidation mein homogeneous catalyst? NO gas.
Enzymes ko catalysts mein kya special banata hai? Extreme specificity (lock-and-key active site), huge rate boosts (1 0 6 1 0 20
Michaelis–Menten rate equation? v = V ma x [ S ] / ( K M + [ S ])
K M Woh substrate concentration jis par v = V ma x /2
Catalyst se speed-up factor (same A, T)? k c a t / k u n = e ( E a , u n − E a , c a t ) / R T
Promoter vs poison kya hota hai? Promoter catalyst ki activity badhata hai; poison use destroy karta hai.
High [ S ] [ S ] Saare active sites saturated (occupied) hote hain, isliye rate V ma x
Arrhenius Equation — yahan everywhere use hone wali e − E a / R T Activation Energy — woh barrier jo catalysts girate hain.Chemical Equilibrium — kyun K e q Rate Law and Order of Reaction — enzyme kinetics dikhata hai ki order [ S ] Adsorption — physi/chemisorption heterogeneous catalysis ko underpin karta hai.Enzymes and Proteins (Biomolecules) — specificity ke peeche biological structure.
via Arrhenius k=A exp -Ea/RT
Forward and backward equally
Heterogeneous different phase
