Class 10 Science · Chapter 1
Short answer: NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations me 8 in-text aur 20 exercise questions hain. Chapter me 5 reaction types padhaye jaate hain — combination, decomposition, displacement, double displacement aur redox — plus corrosion aur rancidity. Neeche har question ka step-by-step balanced solution CBSE marking scheme format me diya gaya hai.
Chapter 1 poore Class 10 Chemistry ki neev hai. Yahan balancing aur reaction types clear ho gaye to Chapter 2 (Acids, Bases and Salts) aur Chapter 3 (Metals and Non-metals) bahut aasan lagenge.
Chapter 1 Summary — 5 Minute Revision
Jab koi substance apni chemical composition badalta hai to use chemical reaction kehte hain. Pehchan ke signs: colour change, gas nikalna, temperature change, state change, ya precipitate banna.
Equation balance kyun karte hain
Law of Conservation of Mass ke according reaction me mass na banta hai na nasht hota hai. Isliye equation ke dono taraf har element ke atoms ki sankhya barabar honi chahiye.
Reaction ke 5 types
| Type | Kya hota hai | Example |
|---|---|---|
| Combination | 2+ substances milkar 1 product | CaO + H2O → Ca(OH)2 |
| Decomposition | 1 substance toot kar 2+ products | CaCO3 → CaO + CO2 |
| Displacement | Zyada reactive metal kam reactive ko hataye | Fe + CuSO4 → FeSO4 + Cu |
| Double displacement | Do compounds ke ions exchange | Na2SO4 + BaCl2 → BaSO4↓ + 2NaCl |
| Redox | Ek oxidise, dusra reduce | CuO + H2 → Cu + H2O |
↔ Table ko side me swipe karein
Exothermic vs Endothermic
- Exothermic — heat release. Respiration, CaO ka water me ghulna, natural gas jalna.
- Endothermic — heat absorb. CaCO3 decomposition, photosynthesis.
Corrosion aur Rancidity
- Corrosion — metal ka hawa/moisture/acid se dheere-dheere kharab hona. Iron pe brown rust, silver pe black, copper pe green layer.
- Rancidity — fats/oils ka oxidise hokar smell aur taste bigadna. Rokne ke liye antioxidants, airtight container, nitrogen flushing, refrigeration.
In-Text Questions — Solutions
Q1. Magnesium ribbon ko jalane se pehle saaf kyun karte hain?
Magnesium reactive metal hai. Hawa me rakhne par surface par magnesium oxide (MgO) ki safed parat jam jaati hai, jo jalne me rukavat daalti hai.
Isliye sandpaper se ragad kar ye oxide layer hataayi jaati hai, taaki magnesium seedha oxygen se react kar sake:
2Mg(s) + O2(g) Δ→ 2MgO(s)
Q2. Balanced equation likhiye
(i) Hydrogen + Chlorine → Hydrogen chloride
H2(g) + Cl2(g) → 2HCl(g)
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Q3. State symbols ke saath balanced equation likhiye
(i) Barium chloride aur sodium sulphate ke solutions milkar insoluble barium sulphate aur sodium chloride solution dete hain:
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
(ii) Sodium hydroxide solution HCl solution se react karke sodium chloride solution aur paani deta hai:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Q4. Whitewashing me use hone wala 'X' kya hai?
(i) Substance 'X' hai calcium oxide (quick lime), formula CaO.
(ii) Paani ke saath reaction — ye exothermic hai, bahut heat nikalti hai:
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
Bana hua calcium hydroxide (slaked lime) deewar par lagaya jata hai. Ye hawa ki CO2 se milkar calcium carbonate ki chamakdaar safed parat banata hai:
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
Q5. Activity 1.7 me ek test tube me gas dugni kyun hoti hai?
Ye electrolysis of water ka experiment hai:
2H2O(l) electricity→ 2H2(g) + O2(g)
Paani ke ek molecule me hydrogen ke 2 atoms aur oxygen ka 1 atom hota hai, isliye hydrogen ki matra oxygen se dugni banti hai. Zyada matra wali gas hydrogen hai, jo cathode par nikalti hai.
Q6. Iron nail daalne par copper sulphate ka rang kyun badalta hai?
Iron, copper se zyada reactive hai, isliye wo copper ko displace kar deta hai — ye displacement reaction hai:
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
CuSO4 ka neela rang khatam hokar FeSO4 ka halka hara rang aa jata hai, aur keel par bhoora copper jam jata hai.
Q7. Double displacement reaction ka ek aur udaharan
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s)↓ + 2KNO3(aq)
Yahan lead iodide ka peela precipitate banta hai.
Q8. Oxidised aur reduced substances pehchaniye
(i) 4Na(s) + O2(g) → 2Na2O(s)
Oxidised: Sodium (Na) — oxygen gain kar raha hai
Reduced: Oxygen (O2)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Oxidised: Hydrogen (H2) — oxygen gain kar raha hai
Reduced: Copper oxide (CuO) — oxygen kho raha hai
Poore Class 10 Science ke handwritten colour notes
IITian & district toppers ke banaye short notes — revision-ready, diagram ke saath. Board se pehle poora syllabus 3 din me revise.
Exercise Questions — Solutions (Q1–Q20)
Q1. 2PbO(s) + C(s) → 2Pb(s) + CO2(g) — kaunse statements galat hain?
Answer: (i) (a) aur (b)
Sahi baat ye hai ki lead oxide (PbO) reduce ho raha hai (oxygen kho raha hai) aur carbon oxidise ho raha hai (oxygen gain kar raha hai).
- (a) "Lead is getting reduced" — galat, lead oxide reduce ho raha hai, lead nahi
- (b) "Carbon dioxide is getting oxidised" — galat, CO2 to product hai
- (c) "Carbon is getting oxidised" — sahi
- (d) "Lead oxide is getting reduced" — sahi
Q2. Fe2O3 + 2Al → Al2O3 + 2Fe kis type ka reaction hai?
Answer: (d) Displacement reaction
Aluminium, iron se zyada reactive hai, isliye wo iron ko uske oxide se displace kar deta hai. Isi ko thermite reaction kehte hain — railway tracks jodne me use hota hai.
Q3. Iron filings me dilute HCl daalne par kya hota hai?
Answer: (a) Hydrogen gas aur iron chloride bante hain
Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)
Q4. Balanced chemical equation kya hai? Balance kyun karte hain?
Balanced chemical equation wo hai jisme reactant side aur product side par har element ke atoms ki sankhya barabar ho.
Balance karne ki wajah: Law of Conservation of Mass ke anusaar kisi bhi chemical reaction me mass na to banaya ja sakta hai na nasht kiya ja sakta hai. Agar equation balanced na ho to ye niyam toot jayega.
Q5. Statements ko chemical equation me badliye aur balance kijiye
(a) Hydrogen gas nitrogen se milkar ammonia banata hai:
3H2(g) + N2(g) → 2NH3(g)
(b) Hydrogen sulphide hawa me jalkar paani aur sulphur dioxide deta hai:
2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
(c) Barium chloride + aluminium sulphate → aluminium chloride + barium sulphate ka precipitate:
3BaCl2(aq) + Al2(SO4)3(aq) → 2AlCl3(aq) + 3BaSO4(s)
(d) Potassium metal paani se react karke potassium hydroxide aur hydrogen deta hai:
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
Q6. Nimn equations ko balance kijiye
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3 (pehle se balanced)
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
Q7. Nimn reactions ke balanced equation likhiye
(a) Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(b) Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2Ag(s)
(c) 2Al(s) + 3CuCl2(aq) → 2AlCl3(aq) + 3Cu(s)
(d) BaCl2(aq) + K2SO4(aq) → BaSO4(s) + 2KCl(aq)
Q8. Balanced equation likhiye aur reaction type bataiye
(a) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(s)
Type: Double displacement
(b) ZnCO3(s) → ZnO(s) + CO2(g)
Type: Decomposition
(c) H2(g) + Cl2(g) → 2HCl(g)
Type: Combination
(d) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Type: Displacement
Q9. Exothermic aur endothermic reactions kya hain?
Exothermic reaction — jisme heat release hoti hai.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + Heat
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
Endothermic reaction — jisme heat absorb hoti hai.
CaCO3(s) + Heat → CaO(s) + CO2(g)
2AgCl(s) sunlight→ 2Ag(s) + Cl2(g)
Q10. Respiration exothermic reaction kyun hai?
Respiration me glucose oxygen ke saath tootkar carbon dioxide, paani aur energy deta hai:
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + Energy
Kyunki is reaction me energy release hoti hai — jisse sharir ka temperature bana rehta hai aur saari activities chalti hain — isliye respiration exothermic hai.
Q11. Decomposition ko combination ka ulta kyun kehte hain?
Combination me do ya zyada substances mil kar ek product banate hain. Decomposition me ek substance toot kar do ya zyada products deta hai. Dono ek dusre ke bilkul ulte hain.
Combination:
CaO(s) + H2O(l) → Ca(OH)2(aq)
2H2(g) + O2(g) → 2H2O(l)
Decomposition:
CaCO3(s) Δ→ CaO(s) + CO2(g)
2H2O(l) electricity→ 2H2(g) + O2(g)
Q12. Heat, light aur electricity se decomposition ke examples
Heat (thermal decomposition):
CaCO3(s) Δ→ CaO(s) + CO2(g)
Light (photolytic decomposition):
2AgBr(s) sunlight→ 2Ag(s) + Br2(g)
Electricity (electrolytic decomposition):
2H2O(l) electricity→ 2H2(g) + O2(g)
Q13. Displacement aur double displacement me antar
| Displacement | Double displacement |
|---|---|
| Zyada reactive element kam reactive ko compound se hata deta hai | Do compounds ke beech ions ka aapsi exchange hota hai |
| Ek element + ek compound involve | Do compounds involve |
| Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) | Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) |
↔ Table ko side me swipe karein
Q14. Silver nitrate se copper dwara silver recovery ka reaction
Copper, silver se zyada reactive hai, isliye wo silver ko displace kar deta hai:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
Ye displacement reaction hai. Solution neela ho jata hai (copper nitrate ki wajah se) aur silver alag jam jata hai.
Q15. Precipitation reaction kya hai?
Wo reaction jisme do solutions mil kar ek insoluble solid (precipitate) banate hain.
Example 1 — safed precipitate:
Na2SO4(aq) + BaCl2(aq) → BaSO4(s)↓ + 2NaCl(aq)
Example 2 — peela precipitate:
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s)↓ + 2KNO3(aq)
Q16. Oxygen ke gain/loss ke aadhar par oxidation aur reduction
(a) Oxidation — oxygen ka gain (ya hydrogen ka loss).
2Cu(s) + O2(g) → 2CuO(s)
2Mg(s) + O2(g) → 2MgO(s)
(b) Reduction — oxygen ka loss (ya hydrogen ka gain).
CuO(s) + H2(g) → Cu(s) + H2O(l)
ZnO(s) + C(s) → Zn(s) + CO(g)
Q17. Chamakdaar bhoora element 'X' hawa me garam karne par kala kyun ho jata hai?
Element 'X' hai copper (Cu). Hawa me garam karne par ye oxygen se react karke copper(II) oxide (CuO) banata hai, jo kale rang ka hota hai:
2Cu(s) + O2(g) Δ→ 2CuO(s)
Q18. Iron ki cheezon par paint kyun lagate hain?
Paint ki parat iron ko hawa ki oxygen aur namee se alag kar deti hai. Iske bina iron rust (Fe2O3·xH2O) ban kar corrode hone lagta hai. Paint se rusting ruk jati hai aur cheez lambe samay tak chalti hai.
Q19. Tel aur fat wale food packets me nitrogen kyun bharte hain?
Nitrogen ek inert (unreactive) gas hai. Packet me nitrogen bharne se andar ki oxygen hat jati hai, jisse tel aur fat oxidise nahi ho paate. Isse rancidity ruk jati hai aur food lambe samay tak taaza rehta hai.
Q20. Corrosion aur Rancidity samjhaiye
(a) Corrosion — jab metal hawa, namee ya acid ke sampark me aakar dheere-dheere kharab hone lagta hai.
Example: Iron par bhoora rust, silver par kali parat, copper par hari parat.
(b) Rancidity — tel ya fat wale khane ka oxidise hokar swad aur smell kharab ho jana.
Example: Purane chips ya ghee ka badbudaar ho jana.
Rokne ke tareeke: antioxidants, airtight container, nitrogen flushing, refrigeration.
Important Equations — Ek Nazar Me
| Reaction | Balanced Equation | Type |
|---|---|---|
| Magnesium jalna | 2Mg + O2 → 2MgO | Combination |
| Quick lime + water | CaO + H2O → Ca(OH)2 | Combination (exothermic) |
| Limestone heating | CaCO3 Δ→ CaO + CO2 | Decomposition (endothermic) |
| Water electrolysis | 2H2O → 2H2 + O2 | Electrolytic decomposition |
| Silver bromide + light | 2AgBr → 2Ag + Br2 | Photolytic decomposition |
| Iron + copper sulphate | Fe + CuSO4 → FeSO4 + Cu | Displacement |
| Thermite reaction | Fe2O3 + 2Al → Al2O3 + 2Fe | Displacement |
| Lead nitrate + KI | Pb(NO3)2 + 2KI → PbI2↓ + 2KNO3 | Double displacement |
| Respiration | C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy | Exothermic / Redox |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Formula badal dena balance karne ke liye. H2O ko H2O2 mat banaiye — sirf coefficient badalte hain, subscript nahi.
- State symbols chhod dena. Question me "state symbols ke saath" likha ho to (s), (l), (g), (aq) na likhne par marks katte hain.
- Q1 me lead vs lead oxide ka confusion. Reduce lead oxide hota hai, lead nahi. Ye har saal galat hota hai.
- Precipitate ka arrow (↓) bhool jana. Precipitation reaction me ↓ ya (s) zaroor likhein.
- Corrosion aur rancidity mila dena. Corrosion metal ka, rancidity fat/oil ki. Dono alag hain.
- Exothermic/endothermic me heat ka side galat. Exothermic me heat product side, endothermic me reactant side.
Board-Style Important Questions
- 1 mark: Thermite reaction ka balanced equation likhiye aur uska ek upyog bataiye.
- 2 marks: Decomposition reaction ki paribhasha dijiye. Heat, light aur electricity se hone wale ek-ek udaharan likhiye.
- 3 marks: Corrosion kya hai? Iron ki rusting rokne ke do tareeke bataiye. Rancidity rokne ka ek tareeka likhiye.
- 5 marks: (i) Displacement aur double displacement me antar, equation ke saath. (ii) Iron nail ko CuSO4 me daalne par kya observe hoga aur kyun?
Quick Quiz — Score Check Karein
Q1. Magnesium ribbon ko jalane se pehle sandpaper se saaf kyun kiya jaata hai?
Q2. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) equation ko balance karne ke baad sodium ka coefficient kya hai?
Q3. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) reaction me copper sulphate ka neela rang kis rang me badalta hai?
Q4. CuO(s) + H2(g) → Cu(s) + H2O(l) reaction me kya oxidise ho raha hai?
Q5. Fe2O3 + 2Al → Al2O3 + 2Fe (thermite reaction) kis type ka reaction hai?
Q6. Pb(NO3)2(aq) + 2KI(aq) → PbI2(s)↓ + 2KNO3(aq) reaction me KI ka balanced coefficient kya hai?
Q7. CaCO3(s) →(Δ) CaO(s) + CO2(g) reaction endothermic kyun hai?
Q8. Iron ki cheezon par paint lagane ka mukhya karan kya hai?
Q9. Food packets me nitrogen gas kyun bhari jaati hai?
Q10. C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + Energy — is reaction (respiration) me oxygen ka coefficient kya hai aur ye reaction kis type ki hai?
Aksar Poochhe Jaane Wale Sawaal
Class 10 Science Chapter 1 me kitne questions hain?
Total 28 questions hain — 8 in-text questions (page 6, 10 aur 13 par) aur 20 exercise questions.
Chapter 1 board exam ke liye kitna important hai?
CBSE har saal ka exact chapter-wise weightage publish nahi karta, isliye koi fixed marks ka daawa karna theek nahi hoga. Itna zaroor hai ki ye chapter poore Chemistry section ki neev hai — reaction types aur balancing aage ke chapters me baar-baar kaam aate hain. Official weightage ke liye CBSE ka latest sample paper dekhein.
Chemical equation balance karne ka sabse aasan tareeka kya hai?
Hit-and-trial method sabse aasan hai. Sabse zyada atoms wale compound se shuru kariye, phir metals, phir non-metals, aur hydrogen-oxygen sabse aakhir me. Yaad rakhiye — sirf coefficient badalna hai, formula nahi.
Thermite reaction kya hai aur kahan use hota hai?
Fe2O3 + 2Al → Al2O3 + 2Fe ek highly exothermic displacement reaction hai. Isme itni heat nikalti hai ki iron pighal jata hai, isliye ise railway tracks aur machine parts weld karne me use kiya jata hai.
Corrosion aur rancidity me kya farak hai?
Corrosion metals me hota hai — hawa aur namee se metal kharab hota hai, jaise iron par rust. Rancidity fats aur oils me hoti hai — oxidation se khane ka swad aur smell bigad jata hai.
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Haan, ye solutions latest NCERT textbook aur CBSE 2026–27 syllabus ke anusaar hain.
Class 10 Science — Saare Chapters
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