WHY? The more reactive metal "wants" the electrons less (gives them up more readily) → it takes the anion's company and shoves out the weaker metal. The reactivity series is the referee.
WHY does it "go"? In solution ions float around freely; the reaction is driven forward when a product leaves the solution — as a precipitate (solid), a gas, or weak electrolyte (water). If nothing leaves, ions just mingle and there's no reaction.
We pretend every bond is fully ionic and hand each shared electron pair to the more electronegative atom. The leftover charge on an atom = its oxidation number. Rules that fall out:
Formation of a precipitate, gas, or water (something leaves solution)
Is neutralisation a double displacement?
Yes — acid + base → salt + water, driven by water formation
Referee that decides displacement direction
The reactivity series (more reactive displaces less reactive)
Oxidising agent is the species that...
Gets reduced (gains electrons itself)
Reducing agent is the species that...
Gets oxidised (loses electrons itself)
Why is combination usually exothermic?
Atoms reach lower-energy, stable configurations, releasing energy
Oxidation number of a free element
Zero
Products of electrolysis of water and their ratio
2H2+O2, ratio H2:O2=2:1
Recall Feynman: explain to a 12-year-old
Think of atoms like LEGO people. Combination = two LEGO guys grab hands to make one bigger guy. Decomposition = a big guy splits back into two — but you have to push him apart (heat, electricity, or light). Displacement = a strong bully walks up to a couple and shoves the weaker partner away to take their place. Double displacement = two couples at a dance swap partners. And redox is a special rule about who gives away tiny electron marbles and who grabs them — one always gives, one always takes, and they trade at the same moment.
Dekho, saari chemical reactions basically atoms ka rearrangement hain — koi atom banta ya mit-ta nahi, isiliye hum equations balance karte hain. Ab in reactions ko unke "pattern" se sort kar lo to sirf 5 cheezein yaad rakhni hain. Combination: do cheezein milke ek ban jaati hain (A+B→AB), jaise Mg jalke MgO banta hai. Decomposition: ek cheez toot ke do banti hai, par isme energy deni padti hai — heat (thermal), bijli (electrolytic), ya light (photo). Displacement: reactivity series ka strong metal weak metal ko compound se bahar dhakel deta hai, jaise loha CuSO4 se copper ko nikaal deta hai. Double displacement: do compounds apne partners swap kar lete hain, aur reaction tabhi aage badhti hai jab kuch solution se nikal jaaye — precipitate, gas, ya paani.
Sabse important confusion: Redox koi 6th shape nahi hai. Redox ka matlab hai electron ka transfer — kisi atom ka oxidation number badalta hai. Yaad rakho OIL RIG: Oxidation Is Loss (electron kho do, oxidation number badhta hai), Reduction Is Gain (electron milta hai, number ghatta hai). Combination aur displacement bhi redox ho sakti hain, par double displacement (jaise neutralisation ya precipitation) usually redox nahi hoti — check karne ka tareeka: oxidation numbers count karo, agar badle to redox.
Exam trick yeh hai ki tumhe products predict karne padte hain. To Forecast-then-Verify karo: reactants dekho, pattern pehchaano, product likho, phir balance aur reactivity se cross-check karo. Jaise Cu+FeSO4 — pehle socho reaction hogi? Cu, Fe se neeche hai series me, to nahi hogi. Yeh soch-samajh ke prediction hi asli skill hai, ratta nahi.
