What is a chemical reaction?

A chemical reaction is a process in which substances (reactants) transform into new substances (products) with different properties.

How to balance chemical equations?

Balance equations by ensuring the number of atoms of each element is equal on both reactant and product sides.

Are these notes useful for competitive exams?

Yes, these notes are perfect for NEET, SSC, Railway, Police Bharti preparation as well as Class 10 board exams.

1. What is a chemical reaction?

Achemical reactionis a process in which one or more substances (reactants) change into new substances (products) with different chemical properties.

2. What is a chemical equation?

Achemical equationrepresents a chemical reaction using symbols and formulas of reactants and products. Example:2H2+ O2→ 2H2O.

3. Why must chemical equations be balanced?

Because of thelaw of conservation of mass: matter is neither created nor destroyed. Balancing ensures the same number of each type of atom on both sides.

4. How do you balance a chemical equation?

Balancing steps: (1) Write correct formulas, (2) Count atoms of each element, (3) Use coefficients to equalize atom counts, (4) Simplify coefficients if possible.

5. What is a combination (or synthesis) reaction?

Acombination reactionis where two or more substances combine to form a single product. Example:2Mg + O2→ 2MgO.

6. What is a decomposition reaction?

Indecomposition, a compound breaks down into two or more simpler substances. Example:2KClO3→ 2KCl + 3O2(on heating).

7. What is a displacement reaction?

In adisplacement reaction, a more reactive element displaces a less reactive element from its compound. Example:Zn + CuSO4→ ZnSO4+ Cu.

8. What is a double displacement reaction?

Indouble displacement, ions of two compounds exchange places to form new compounds. Example:AgNO3+ NaCl → AgCl↓ + NaNO3(AgCl precipitates).

9. What is an exothermic reaction?

Anexothermic reactionreleases heat to the surroundings. Example: combustion of methane:CH4+ 2O2→ CO2+ 2H2O + heat.

10. What is an endothermic reaction?

Anendothermic reactionabsorbs heat from the surroundings. Example: photosynthesis overall is endothermic.

11. What are oxidation and reduction?

Oxidationis loss of electrons (or gain of oxygen/loss of hydrogen).Reductionis gain of electrons (or loss of oxygen/gain of hydrogen). They occur together.

12. What is a redox reaction?

Aredox reactioninvolves simultaneous oxidation and reduction. Example:CuO + H2→ Cu + H2O(CuO reduced, H2oxidised).

13. What is the activity (reactivity) series of metals?

Theactivity seriesranks metals by reactivity. A more reactive metal can displace a less reactive metal from its salt solution (e.g., Zn displaces Cu).

14. What is a precipitation reaction?

When two soluble salts react to form an insoluble solid (precipitate). Example:BaCl2+ Na2SO4→ BaSO4↓ + 2NaCl.

16. What is corrosion?

Corrosionis the gradual destruction of metals by chemical reactions with air, water or other chemicals — e.g., iron rusting.

17. How can corrosion be prevented?

Methods: painting, galvanising (coating with Zn), electroplating, alloying (e.g., stainless steel), and sacrificial protection (using a more reactive metal).

18. What is rancidity?

Rancidityis the process where fats and oils become unpleasant in smell/taste due to oxidation. Prevention: storing in airtight containers, refrigeration, adding antioxidants.

21. What is combustion?

Combustionis a rapid exothermic reaction of a substance with oxygen producing heat and light. Example: burning of candle or wood.

22. What is complete combustion?

Incomplete combustion, a hydrocarbon reacts with excess oxygen to form CO2and H2O only. Example:CH4+ 2O2→ CO2+ 2H2O.

23. What is incomplete combustion?

Inincomplete combustion, limited oxygen causes formation of CO (carbon monoxide), soot (carbon) and less energy released. Example: burning of fuel in a poorly ventilated room.

Class 10 Science — Chapter 1: Chemical Reactions & Equations

By RAAM SETU | NEET, SSC, Railway & Police Bharti Focused Notes 📘

📘 Introduction

This chapter explains Chemical Reactions & Equations including types of reactions, balancing equations, and examples. Essential for NEET, SSC, Railway, Police Bharti exams and Class 10 board exams.

🔹 Key Concepts

Reactants & Products: Substances before and after reaction
Types of Reactions: Combination, Decomposition, Displacement, Double Displacement, Redox, etc.
Balancing Equations: Ensuring atom count is equal on both sides
Indicators: Substances that show changes during reactions

📊 Chapter Summary Table

Reaction Type	Example	Key Feature
Combination	A + B → AB	Two reactants form one product
Decomposition	AB → A + B	One reactant splits into two
Displacement	A + BC → AC + B	One element replaces another
Double Displacement	AB + CD → AD + CB	Exchange of ions

🧮 Practice Questions

Balance the equation: H₂ + O₂ → H₂O
Classify: Zn + HCl → ZnCl₂ + H₂
Write an example of a double displacement reaction.
Explain how to identify reactants and products in a chemical equation.
Balance the equation: Fe + O₂ → Fe₂O₃

Chemical Reactions & Equations — 50 Q&A

Based on NCERT — Chapter 1. Tap any question to expand the answer. Toggle theme to switch Light / Dark.

Light / Dark

Made for NCERT 10th — Chapter: Chemical Reactions & Equations

📘 Introduction

🔹 Key Concepts

📊 Chapter Summary Table

🧮 Practice Questions

1. What is a chemical reaction?

2. What is a chemical equation?

3. Why must chemical equations be balanced?

4. How do you balance a chemical equation?

5. What is a combination (or synthesis) reaction?

6. What is a decomposition reaction?

7. What is a displacement reaction?

8. What is a double displacement reaction?

9. What is an exothermic reaction?

10. What is an endothermic reaction?

11. What are oxidation and reduction?

12. What is a redox reaction?

13. What is the activity (reactivity) series of metals?

14. What is a precipitation reaction?

15. Give an example of a combination reaction from everyday life.

16. What is corrosion?

17. How can corrosion be prevented?

18. What is rancidity?

19. Give an example of double displacement reaction.

20. Give an example of decomposition reaction.

21. What is combustion?

22. What is complete combustion?

23. What is incomplete combustion?

24. How can you test for hydrogen gas?

25. How can you test for oxygen gas?

26. How can you test for carbon dioxide?

27. What is a neutralisation reaction?

28. What happens when Zn is added to CuSO4 solution?

29. Which metal will displace hydrogen from dilute acids — Zn or Cu?

30. What does aqueous solution mean?

31. What is a catalyst?

32. Why is the activity series useful?

33. What is an ionic equation and a net ionic equation?

34. What are spectator ions?

35. What is a word equation?

36. How do you convert a word equation to a chemical equation?

37. How can you identify the type of a reaction?

38. Give a redox reaction example from daily life.

39. Give an example where a metal reacts with an acid to produce hydrogen.

40. What role does oxygen play in combustion?

41. What is a catalytic converter (brief) and how is it related to reactions?

42. Write a simplified chemical equation for rusting of iron.

43. State the law of conservation of mass.

44. Give an everyday example of neutralisation.

45. Write the reaction when iron reacts with copper sulfate solution.

46. How is galvanisation related to preventing corrosion?

47. Give an example where colour change indicates a chemical reaction.

48. Give an example of a gas-evolution reaction.

49. Balance the chemical equation: H2 + O2 → H2O

50. Why are chemical equations important in chemistry?

28. What happens when Zn is added to CuSO₄ solution?

49. Balance the chemical equation: H₂ + O₂ → H₂O