Types of reactions — combination, decomposition, displacement, double displacement, redox

1.3.2 · Chemistry › Chemical Reactions & Stoichiometry

The 5 patterns at a glance

Figure — Types of reactions — combination, decomposition, displacement, double displacement, redox

Pattern	Skeleton	Memory hook
Combination	$A + B \to A B$	do se ek banta hai
Decomposition	$A B \to A + B$	ek se do bante hain
Displacement	$A + B C \to A C + B$	ek akela element doosre ko bahar nikalta hai
Double displacement	$A B + C D \to A D + C B$	partners swap karte hain
Redox	electron transfer	koi shape nahi — doosron par ek lens hai

1. Combination reaction

WHY hota hai? Atoms combine hote hain lower energy / stable electron configurations tak pahunchne ke liye, usually energy release karke (zyaatar combinations exothermic hote hain).

2. Decomposition reaction

Energy source sub-type ka naam deta hai:

Thermal decomposition (heat, "thermolysis")
Electrolytic decomposition (electricity, "electrolysis")
Photo decomposition (light, "photolysis")

WHY? Zyada reactive metal "electrons kam chahta" hai (unhe zyada aasani se deta hai) → woh anion ki company le leta hai aur kamzor metal ko bahar dhakela deta hai. Reactivity series referee hai.

Reactivity (metals, decreasing): $K > N a > C a > M g > A l > Z n > F e > P b > (H) > C u > A g > A u$

4. Double displacement reaction

WHY "go" karta hai? Solution mein ions freely float karte hain; reaction tab aage barhti hai jab ek product solution chhod deta hai — precipitate (solid) ke roop mein, gas ke roop mein, ya weak electrolyte (water) ke roop mein. Agar kuch nahi jaata, toh ions bas milte hain aur koi reaction nahi hoti.

5. Redox reaction (the electron lens)

Oxidation numbers pehle principles se derive karna

Hum pretend karte hain ki har bond fully ionic hai aur har shared electron pair zyada electronegative atom ko de dete hain. Atom par bacha hua charge = uska oxidation number. Jo rules nikalte hain:

Free element = $0$ (jaise $M g$ , $O_{2}$ ).
Simple ion = uska charge ( $N a^{+} = + 1$ ).
O usually $- 2$ hota hai, H usually $+ 1$ .
Oxidation numbers ka sum = overall charge.

Forecast-then-Verify drill

Recall Products predict karo, phir check karo

$H_{2} + C l_{2} \to ?$ → Combination + redox → $2 H C l$
$2 P b (N O_{3})_{2} Δ ?$ → Thermal decomposition → $2 P b O + 4 N O_{2} + O_{2}$
$A g N O_{3} + N a C l \to ?$ → Double displacement (precipitate) → $A g C l ↓ + N a N O_{3}$
$C u + 2 A g N O_{3} \to ?$ → Displacement + redox → $C u (N O_{3})_{2} + 2 A g$

Flashcards

Combination reaction ka skeleton

A + B \to A B

(do ya zyada → ek product)

Decomposition ka skeleton

A B \to A + B

(ek → do ya zyada, energy chahiye)

Displacement ka skeleton

A + B C \to A C + B

, A, B se zyada reactive hai

Double displacement ka skeleton

A B + C D \to A D + C B

(partners swap karte hain)

Oxidation ki definition (electron view)

Electrons ki loss / oxidation number badhta hai

Reduction ki definition (electron view)

Electrons ki gain / oxidation number ghatta hai

Redox ke liye mnemonic

OIL RIG — Oxidation Is Loss, Reduction Is Gain

Decomposition ke teen energy sub-types

Thermal (heat), Electrolytic (electricity), Photolytic (light)

Double displacement ko aage kya drive karta hai

Precipitate, gas, ya water ka banana (kuch solution chhod deta hai)

Kya neutralisation ek double displacement hai?

Haan — acid + base → salt + water, water formation se drive hota hai

Displacement direction decide karne wala referee

Reactivity series (zyada reactive, kam reactive ko displace karta hai)

Oxidising agent woh species hai jo...

Reduce hoti hai (khud electrons gain karti hai)

Reducing agent woh species hai jo...

Oxidise hoti hai (khud electrons lose karti hai)

Combination usually exothermic kyun hoti hai?

Atoms lower-energy, stable configurations tak pahunchte hain, energy release karke

Free element ka oxidation number

Zero

Water ke electrolysis ke products aur unka ratio

2 H_{2} + O_{2}

, ratio

H_{2} : O_{2} = 2 : 1

Recall Feynman: ek 12-saal ke bacche ko samjhao

Atoms ko LEGO logon ki tarah socho. Combination = do LEGO guys haath milate hain ek bade bande banne ke liye. Decomposition = ek bada banda wapas do mein split hota hai — lekin tumhe use push karna padta hai (heat, electricity, ya light se). Displacement = ek strong bully ek couple ke paas aata hai aur kamzor partner ko dhakka dekar unki jagah le leta hai. Double displacement = do couples dance mein partners swap karte hain. Aur redox ek special rule hai ki kaun chhote electron marbles deta hai aur kaun leta hai — ek hamesha deta hai, ek hamesha leta hai, aur woh usi waqt trade karte hain.

Connections

Balancing Chemical Equations — har pattern mass conservation ko maanta hai.
Reactivity Series of Metals — displacement direction decide karta hai.
Oxidation Number Rules — redox detect karne ka tool.
Acids, Bases and Salts — double displacement ke roop mein neutralisation.
Electrolysis — electrolytic decomposition gehrai mein.
Exothermic and Endothermic Reactions — in patterns mein energy andar/bahar jaana.

Types of reactions — combination, decomposition, displacement, double displacement, redox

The 5 patterns at a glance

1. Combination reaction

2. Decomposition reaction

3. Displacement reaction

4. Double displacement reaction

5. Redox reaction (the electron lens)

Oxidation numbers pehle principles se derive karna

Forecast-then-Verify drill

Flashcards

Connections

Concept Map