Class 10 Science – Chapter 1: Chemical Reactions and Equations
1. Introduction to Chemical Reactions
A chemical reaction is a process in which reactants transform into products.
Example: Rusting of iron
Fe + O2 + H2O → Fe2O3 . xH2O
2. Chemical Equations
A chemical equation represents a reaction using symbols.
Example: Magnesium burns in oxygen
Mg + O2 → MgO
Balanced vs. Unbalanced Equations
Unbalanced: H2 + O2 → H2O
Balanced: 2H2 + O2 → 2H2O
3. Types of Chemical Reactions
Combination Reaction
Two or more reactants combine to form a single product.
CaO + H2O → Ca(OH)2
Decomposition Reaction
A single reactant breaks down into two or more products.
2H2O → 2H2 + O2
Displacement Reaction
A more reactive element displaces a less reactive element from its compound.
Zn + CuSO4 → ZnSO4 + Cu
Double Displacement Reaction
Two compounds exchange their ions to form two new compounds.
AgNO3 + NaCl → AgCl + NaNO3
Oxidation and Reduction (Redox) Reaction
Oxidation is the addition of oxygen or removal of hydrogen, while reduction is the removal of oxygen or addition of hydrogen.
CuO + H2 → Cu + H2O
4. Important MCQs
1. What is the reaction called when two or more reactants combine to form a single product?
A) Decomposition reaction
B) Combination reaction
C) Displacement reaction
D) Redox reaction
Answer: B) Combination reaction
2. Which of the following is a decomposition reaction?
A) CaO + H2O → Ca(OH)2
B) 2H2O → 2H2 + O2
C) Zn + CuSO4 → ZnSO4 + Cu
D) AgNO3 + NaCl → AgCl + NaNO3
Answer: B) 2H2O → 2H2 + O2
3. What is the chemical formula for rust?
A) FeO
B) Fe2O3 . xH2O
C) Fe(OH)3
D) FeSO4
Answer: B) Fe2O3 . xH2O
4. What type of reaction is: Zn + CuSO4 → ZnSO4 + Cu?
Answer: Displacement reaction
5. Which gas is evolved when zinc reacts with dilute hydrochloric acid?
Answer: Hydrogen gas
6. What is the color change observed in rusting of iron?
Answer: Reddish-brown
7. Which of the following is an example of a double displacement reaction?
Answer: AgNO3 + NaCl → AgCl + NaNO3
8. What prevents rancidity in food?
Answer: Antioxidants
9. Which reaction is also known as a redox reaction?
Answer: Oxidation and Reduction reaction
10. What is the effect of oxidation on metals?
Answer: Corrosion