Writing and balancing chemical equations

1.3.1 · Chemistry › Chemical Reactions & Stoichiometry

Hum balance karte HI KYUN hain?

Ye KYUN matter karta hai: Agar Hydrogen aur Oxygen milke paani banate hain, toh jo 2 H atoms aur 1 O atom tumhare paas shuru mein the, woh baad mein bhi exist karte rahenge — bas alag tarah se bonded hoke. Ek unbalanced equation yeh claim karti hai ki atoms gaayab ho gaye ya kahin se aa gaye, jo physically galat hai.

Ek equation ke PARTS kya hote hain?

$reactants 2 H_{2} + O_{2} ⟶ products 2 H_{2} O$

Coefficient (aage wala bada number, jaise 2) — balance karne ke liye tum ise BADAL SAKTE ho.
Subscript (chota number, jaise H₂) — ise tum KABHI NAHI badal sakte; yeh substance ko define karta hai.
State symbols: $(s)$ solid, $(l)$ liquid, $(g)$ gas, $(a q)$ paani mein ghula hua.
Arrow $\to$ matlab "yields". Double arrow $⇌$ reversible reaction ko dikhata hai.

Figure — Writing and balancing chemical equations

Balance KAISE karein — ek reliable recipe

O aur H ko last ke liye KYUN bachate hain? Ye usually sabse zyaada compounds mein appear karte hain (paani, oxides, acids), isliye baaki sab fix karne ke baad ye final "adjustable slack" ki tarah rehte hain.

Example 1 — Methane ka combustion

Skeleton: $C H_{4} + O_{2} \to C O_{2} + H_{2} O$

Step	Action	Yeh step KYUN?
C	1 C left, 1 C right ✓	Sabse rare element pehle balance karo
H	4 H left → right pe 4 H chahiye → $2 H_{2} O$	$2 \times 2 = 4$ H
O	Abhi: $2 (from C O_{2}) + 2 (from 2 H_{2} O) = 4$ O → $2 O_{2}$ rakh do	O last: product side pe O sum karo

Balanced: $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ Check: C 1=1, H 4=4, O 4=4 ✓

Example 2 — Fractions ke saath rusting-style

Skeleton: $F e + O_{2} \to F e_{2} O_{3}$

Step	Action	Kyun?
Fe	Right pe 2 Fe → left pe $2 F e$	metals pehle
O	Right pe 3 O, har $O_{2}$ mein 2 → $\frac{3}{2} O_{2}$ chahiye	fractions temporarily allowed hain
Clear	×2 sab cheez	final form mein integer coefficients zaroori hain

$4 F e + 3 O_{2} \to 2 F e_{2} O_{3}$ Check: Fe 4=4, O 6=6 ✓ — ×2 KYUN? $\frac{3}{2} O_{2}$ matlab "1.5 molecules," physically impossible hai, isliye scale up karo.

Example 3 — Polyatomic ion as a unit

Skeleton: $A l + H_{2} S O_{4} \to A l_{2} (S O_{4})_{3} + H_{2}$

Step	Action	Kyun?
$S O_{4}$	Right pe 3 sulfate → $3 H_{2} S O_{4}$	$S O_{4}$ ko ek block maano, split mat karo
Al	Right pe 2 Al → $2 A l$	metal
H	Left $3 \times 2 = 6$ H → $3 H_{2}$ chahiye	H last

$2 A l + 3 H_{2} S O_{4} \to A l_{2} (S O_{4})_{3} + 3 H_{2}$ Check: Al 2=2, S 3=3, O 12=12, H 6=6 ✓

Forecast-then-Verify drill

Recall Feynman: ek 12-saal ke bachche ko samjhao

Socho tumhare paas LEGO blocks hain aur tum ek car banate ho. Phir use tod ke ek boat banate ho. Tum blocks kho nahi sakte ya jadu se naye nahi pa sakte — tumhe exact wahi same pieces use karni padti hain. Ek chemical equation ek promise hai ki humne har LEGO block ko pehle aur baad mein count kiya, aur counts match karte hain. Hum sirf yeh decide karte hain ki kitni cars aur kitni boats (coefficients), individual blocks kabhi nahi todte (subscripts).

Flashcards

Ek chemical equation balance kyun honi chahiye?

Law of Conservation of Mass ki wajah se — atoms na bante hain na destroy hote hain, isliye dono sides par atom counts equal hone chahiye.

Equation balance karne ke liye tum kya badal sakte ho, aur kya KABHI nahi badal sakte?

Tum coefficients badal sakte ho; subscripts KABHI nahi badal sakte (woh substance ki identity change kar deta hai).

Balancing order mein kaun se elements pehle aur kaun se last mein hote hain?

Metals pehle, phir non-metals, phir hydrogen, phir oxygen sabse last.

Balance karo:

C H_{4} + O_{2} \to C O_{2} + H_{2} O

C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O

Balance karo:

F e + O_{2} \to F e_{2} O_{3}

4 F e + 3 O_{2} \to 2 F e_{2} O_{3}

Balance karo:

C_{3} H_{8} + O_{2} \to C O_{2} + H_{2} O

C_{3} H_{8} + 5 O_{2} \to 3 C O_{2} + 4 H_{2} O

Ek polyatomic ion jaise

S O_{4}^{2 -}

jo intact rehta hai, usse kaise handle karte hain?

Use ek single unit ki tarah treat karo aur ek token ki tarah balance karo.

(s), (l), (g), (a q)

ka matlab kya hai?

Solid, liquid, gas, aqueous (paani mein ghula hua).

Hum kabhi kabhi fractional coefficients KYUN use karte hain, aur baad mein kya karte hain?

Odd atom count (jaise O) balance karne ke liye; baad mein sab coefficients ko sabse chote integer se multiply karke fractions clear karte hain.

Element E ke liye general balance condition kya hai?

\sum_{r e a c t an t s} (coeff \times subscript) = \sum_{p r o d u c t s} (coeff \times subscript)

Hum balance karte HI KYUN hain?

Ek equation ke PARTS kya hote hain?

Balance KAISE karein — ek reliable recipe

Example 1 — Methane ka combustion

Example 2 — Fractions ke saath rusting-style

Example 3 — Polyatomic ion as a unit

Forecast-then-Verify drill

Flashcards

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Concept Map