CBSE Class 10 Chemistry Chemical Reactions And Equations Worksheet Set 08

This is Printable Worksheet Set 08 for CBSE Class 10 Chemistry Chapter 1, Chemical Reactions and Equations, with 18 questions and answers in an easy-to-print layout. It practises fill in the blanks on types of reactions, exothermic and endothermic changes, oxidation and reduction, rancidity and corrosion, and a matching question on reaction types.

Fill in the Blanks

Question 1. Fill in the blank: In a ________ reaction, two or more substances combine to form a new single substance.
Answer:
combination
Two or more reactants join to form one product, so this is a combination reaction.
Example: 2Mg + O₂ → 2MgO.
In simple words: Many reactants, one product.

Teacher's Note:
1. Combination reactions are generally exothermic.
2. Do not confuse it with a decomposition reaction, which is the reverse.

Question 2. Fill in the blank: Reactions in which heat is given out along with the products are called ________ reactions.
Answer:
exothermic
Reactions that release heat are called exothermic reactions.
Example: CaO + H₂O → Ca(OH)₂ + heat.
In simple words: Heat is released.

Teacher's Note:
1. Burning, respiration and neutralisation are exothermic.
2. Write "+ heat" on the product side of the equation.

Question 3. Fill in the blank: Reactions in which energy is absorbed are known as ________ reactions.
Answer:
endothermic
Reactions that absorb energy from the surroundings are called endothermic reactions.
Example: CaCO₃ → CaO + CO₂ (heat is absorbed).
In simple words: Heat is taken in.

Teacher's Note:
1. Photosynthesis and thermal decomposition are endothermic.
2. Write "− heat" or "heat" on the reactant side.

Question 4. Fill in the blank: When an element displaces another element from its compound, a ________ reaction occurs.
Answer:
displacement
A more reactive element pushes out a less reactive element from its compound.
This is a displacement reaction, for example Fe + CuSO₄ → FeSO₄ + Cu.
In simple words: A stronger element replaces a weaker one.

Teacher's Note:
1. Use the reactivity series to predict the reaction.
2. Zinc displaces copper but copper cannot displace zinc.

Question 5. Fill in the blank: Two different atoms or groups of atoms (ions) are exchanged in ________ reactions.
Answer:
double displacement
When two compounds exchange their ions, the reaction is a double displacement reaction.
Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl.
In simple words: Two compounds swap partners.

Teacher's Note:
1. Precipitation and neutralisation are double displacement reactions.
2. Both reactants are usually in solution.

Question 6. Fill in the blank: Precipitation reactions produce ________ salts.
Answer:
insoluble
In a precipitation reaction an insoluble solid separates from the solution.
So the salts formed are insoluble salts, for example BaSO₄ and PbI₂.
In simple words: A solid settles out of the solution.

Teacher's Note:
1. The solid formed is called the precipitate.
2. A downward arrow (↓) marks a precipitate in an equation.

Question 7. Fill in the blank: Reduction is the ________ of oxygen or gain of hydrogen.
Answer:
loss
Reduction means removal of oxygen or addition of hydrogen.
So reduction is the loss of oxygen, for example CuO + H₂ → Cu + H₂O.
In simple words: Reduction removes oxygen.

Teacher's Note:
1. Oxidation and reduction always occur together.
2. In CuO + H₂, CuO is reduced and H₂ is oxidised.

Question 8. Fill in the blank: The digestion of food in the body is an example of ________ reaction.
Answer:
decomposition
Large food molecules break into simpler molecules such as glucose and amino acids.
So digestion is a decomposition reaction.
In simple words: Big molecules break into small ones.

Teacher's Note:
1. Enzymes help in this breakdown.
2. Respiration that follows is an exothermic reaction.

Question 9. Fill in the blank: The addition of oxygen to a substance is called ________.
Answer:
oxidation
Gain of oxygen (or loss of hydrogen) is oxidation.
Example: 2Cu + O₂ → 2CuO.
In simple words: Gaining oxygen is oxidation.

Teacher's Note:
1. Remember: OIL, Oxidation Is Loss of hydrogen or Gain of oxygen.
2. Corrosion and rancidity are oxidation reactions.

Question 10. Fill in the blank: When calcium carbonate is heated, it decomposes to give ________ and ________.
Answer:
calcium oxide (quicklime) and carbon dioxide
Heating breaks CaCO₃ into two simpler substances.
CaCO₃ →^heat CaO + CO₂. The products are calcium oxide and carbon dioxide.
In simple words: Limestone gives quicklime and CO₂ on heating.

Teacher's Note:
1. This is a thermal decomposition reaction.
2. It is endothermic as heat is absorbed.

Question 11. Fill in the blank: The new substances produced in a chemical reaction are called ________.
Answer:
products
Substances that take part in a reaction are reactants; the new substances formed are products.
In simple words: Products are what we get after the reaction.

Teacher's Note:
1. Reactants are written on the left and products on the right of the arrow.
2. Products have properties different from reactants.

Question 12. Fill in the blank: Two antioxidants which are usually added to fat and oil containing foods to prevent rancidity are ________ and ________.
Answer:
BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene)
Antioxidants stop the oxidation of fats and oils.
Common food antioxidants are BHA and BHT.
In simple words: These chemicals keep fatty food fresh.

Teacher's Note:
1. Rancidity is the oxidation of fats and oils.
2. Packing in nitrogen and refrigeration also delay rancidity.

Question 13. Fill in the blank: In the reaction SO₂ + 2H₂S → 2H₂O + 3S, SO₂ is acting as a(n) ________ agent.
Answer:
oxidising
SO₂ gives up oxygen and gets reduced to sulphur.
A substance that is itself reduced and oxidises the other reactant is an oxidising agent. H₂S is oxidised to S.
In simple words: SO₂ oxidises H₂S and itself is reduced.

Teacher's Note:
1. Oxidising agent: gets reduced.
2. Reducing agent: gets oxidised.

Question 14. Fill in the blank: Na₂SO₄ + BaCl₂ → ________ + 2NaCl
Answer:
BaSO₄
In a double displacement reaction the ions exchange partners.
Ba²⁺ joins SO₄²⁻ to give BaSO₄, a white precipitate: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl.
In simple words: The white precipitate is barium sulphate.

Teacher's Note:
1. Balance Na and Cl to check: Na 2 = 2 and Cl 2 = 2.
2. BaSO₄ is insoluble in water.

Question 15. Fill in the blank: A balanced chemical equation has equal masses of various elements in ________ and ________.
Answer:
reactants and products
By the law of conservation of mass, the mass of each element is the same before and after the reaction.
So the masses are equal in the reactants and products.
In simple words: Nothing is lost or gained in a reaction.

Teacher's Note:
1. Count atoms of every element on both sides.
2. Never change a formula to balance an equation.

Question 16. Fill in the blank: ________ is the process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface.
Answer:
Corrosion
The slow destruction of a metal by air, moisture or chemicals is corrosion.
Examples: rusting of iron and the green coating on copper.
In simple words: Metals slowly get eaten away.

Teacher's Note:
1. Rusting is the corrosion of iron.
2. Painting and galvanising prevent corrosion.

Question 17. Fill in the blank: The colour of ferrous sulphate crystals before heating is ________ and the colour of the residue after strong heating is ________.
Answer:
green; reddish-brown (ferric oxide)
Ferrous sulphate crystals are green.
On strong heating they decompose: 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃, leaving reddish-brown ferric oxide and giving the smell of burning sulphur.
In simple words: Green crystals turn brown on heating.

Teacher's Note:
1. Hold the boiling tube away from your face during the experiment.
2. This is a thermal decomposition reaction.

Match the Following

Question 18. Match the following. Column II gives the type of reaction mentioned in Column I.
Column I: (A) C + O₂ → CO₂; (B) AgBr →^light Ag + Br₂; (C) Zn + CuSO₄ → ZnSO₄ + Cu; (D) CH₃CH₂OH →^Cu CH₃CHO + H₂.
Column II: (p) Displacement; (q) Combination; (r) Decomposition; (s) Oxidation.
Answer:
(A) → (q): two substances (C and O₂) join to give one product, a combination reaction.
(B) → (r): AgBr breaks into Ag and Br₂ in light, a decomposition reaction.
(C) → (p): Zn displaces Cu from its salt, a displacement reaction.
(D) → (s): ethanol loses hydrogen, so it is oxidised to ethanal.
In simple words: Match each equation with what happens in it: join, split, replace, or lose hydrogen.

Teacher's Note:
1. Check the number of reactants and products first.
2. Loss of hydrogen is also oxidation.