Combustion stoichiometry — fuel + O₂ → CO₂ + H₂O

1.3.9 · Chemistry › Chemical Reactions & Stoichiometry

Core idea

General formula scratch se derive karna

Ek generic fuel lo $C_{x} H_{y} O_{z}$ (ek molecule jisme $x$ carbons, $y$ hydrogens, $z$ oxygens hain). Hum chahte hain:

$C_{x} H_{y} O_{z} + a O_{2} ⟶ b CO_{2} + c H_{2} O$

Step 1 — Carbon balance. Kyun? Har C atom CO₂ mein jaana chahiye, aur har CO₂ mein 1 C hota hai. $x = b \Rightarrow b = x$

Step 2 — Hydrogen balance. Kyun? Har H ko H₂O mein jaana chahiye, aur har H₂O mein 2 H hote hain. $y = 2 c \Rightarrow c = \frac{y}{2}$

Step 3 — Oxygen balance (last!) Kyun last? O₂ O ka ek-maatra free source hai, isliye hum $a$ ke liye solve karte hain jab products fix ho jaate hain. Right side pe O atoms count karo, fuel ke andar jo O pehle se hai use minus karo: $from O_{2} 2 a + fuel’s O z = in CO_{2} 2 b + in H_{2} O c$ $b = x$ , $c = y /2$ substitute karo: $2 a + z = 2 x + \frac{y}{2} \Rightarrow a = x + \frac{y}{4} - \frac{z}{2}$

Figure — Combustion stoichiometry — fuel + O₂ → CO₂ + H₂O

Worked examples

Common mistakes (Unhe steel-man karo)

Recall Feynman: ek 12-saal ke bachche ko samjhao

LEGO bricks imagine karo. Tumhara fuel kale (carbon) aur safed (hydrogen) bricks ka ek guchha hai. Aag laal bricks laati hai (oxygen). Game ka rule hai: jo bhi brick se start karo use hamesha use karo, koi bhi throw away mat karo. Har kala brick do laal bricks pakad leta hai aur " $CO_{2}$ " piece ban jaata hai. Har do safed bricks ek laal brick pakad lete hain aur " $H_{2} O$ " piece ban jaati hai. Tum bas count karo kitni laal bricks chahiye thi — wahi tumhara oxygen hai. Agar tumhare fuel mein pehle se kuch laal bricks lagi hoti hain, toh tumhe bahar se kam laani padengi. Bas yahi trick hai!

Recall checkpoint

Flashcards

General combustion equation for

C_{x} H_{y} O_{z}

C_{x} H_{y} O_{z} + (x + \frac{y}{4} - \frac{z}{2}) O_{2} \to x C O_{2} + \frac{y}{2} H_{2} O

Combustion equation balance karne ka order kya hai?

Pehle Carbon, phir Hydrogen, aur Oxygen sabse last

Methane CH₄ ke liye O₂ coefficient kya hai?

2 (yaani

1 + 4/4

)

Alcohols ko same C,H wale hydrocarbons se kam O₂ kyun chahiye?

Unme pehle se O atoms hote hain, jo

- z /2

credit deta hai

Complete combustion hamesha kaun se do products deta hai?

CO₂ aur H₂O (saare C aur H fully oxidized)

CO ya soot ka banana kya indicate karta hai?

Incomplete combustion (insufficient O₂)

y hydrogens wale fuel molecule se kitne H₂O molecules bante hain?

y /2

Octane C₈H₁₈ ke liye balanced eq (whole numbers)

2 C_{8} H_{18} + 25 O_{2} \to 16 C O_{2} + 18 H_{2} O

1 mol CH₄ jalane ke liye O₂ ka mass kitna hoga?

64 g (2 mol × 32 g/mol)

Balancing ko kaun sa conservation law kaam karta banata hai?

Conservation of mass / atoms (Lavoisier)

Connections

Law of Conservation of Mass — woh reason jiske wajah se atoms balance hone chahiye.
Mole Concept and Molar Mass — coefficients ↔ grams convert karta hai.
Limiting Reagent — decide karta hai complete vs incomplete combustion.
Enthalpy of Combustion — atoms rearrange hone par release hone wali energy.
Oxidation States — C low oxidation state se CO₂ mein $+ 4$ par jaata hai.
Balancing Chemical Equations — general method; combustion ek special case hai.