Chemical Reactions and Equations Important Questions.

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1. Q1Easy

   Which of the following is an example of a combination reaction?

   • A.C(s) + O2(g) → CO2(g)
   • B.2H2O(l) → 2H2(g) + O2(g)
   • C.2AgBr(s) → 2Ag(s) + Br2(g)
   • D.Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
   Answer: C(s) + O2(g) → CO2(g)

   Explanation: Combination reactions occur when two or more substances combine to form a single product. Burning coal is a classic example of this type of reaction.

2. Q2Easy

   Which reaction is an example of an exothermic reaction?

   • A.2H2(g) + O2(g) → 2H2O(l)
   • B.C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
   • C.2AgBr(s) → 2Ag(s) + Br2(g)
   • D.CaCO3(s) → CaO(s) + CO2(g)
   Answer: 2H2(g) + O2(g) → 2H2O(l)

   Explanation: Exothermic reactions release heat. The formation of water from hydrogen and oxygen is an example of this type of reaction, releasing a significant amount of heat.

3. Q3Easy

   Which of the following is an observable sign of a chemical reaction?

   • A.Change in state
   • B.Change in color
   • C.Evolution of a gas
   • D.Change in temperature
   Answer: Evolution of a gas

   Explanation: Evolution of gas is one of the observable signs of a chemical reaction, along with changes in state, color, and temperature.

4. Q4Easy

   Which of the following is used for whitewashing walls?

   • A.Calcium hydroxide
   • B.Calcium carbonate
   • C.Calcium oxide
   • D.Calcium sulfate
   Answer: Calcium hydroxide

   Explanation: Calcium hydroxide, also known as slaked lime, is commonly used for whitewashing walls.

5. Q5Medium

   Which of the following reactions is a displacement reaction?

   • A.Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
   • B.2H2(g) + O2(g) → 2H2O(l)
   • C.Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
   • D.C(s) + O2(g) → CO2(g)
   Answer: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

   Explanation: In a displacement reaction, one element displaces another from its compound. Here, iron displaces copper from copper sulfate solution.

6. Q6Medium

   What type of reaction is represented by the equation: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)?

   • A.Combination reaction
   • B.Decomposition reaction
   • C.Displacement reaction
   • D.Double displacement reaction
   Answer: Combination reaction

   Explanation: This reaction involves two reactants combining to form a single product, which is characteristic of combination reactions.

7. Q7Medium

   Which type of reaction is indicated by the reaction: 2AgBr(s) → 2Ag(s) + Br2(g)?

   • A.Combination reaction
   • B.Decomposition reaction
   • C.Exothermic reaction
   • D.Endothermic reaction
   Answer: Decomposition reaction

   Explanation: In this reaction, a single compound breaks down into simpler substances, which is characteristic of a decomposition reaction.

8. Q8Medium

   Which reaction is an example of an endothermic reaction?

   • A.2H2(g) + O2(g) → 2H2O(l)
   • B.C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
   • C.2AgBr(s) → 2Ag(s) + Br2(g)
   • D.CaCO3(s) → CaO(s) + CO2(g)
   Answer: 2AgBr(s) → 2Ag(s) + Br2(g)

   Explanation: Endothermic reactions absorb energy. The decomposition of silver bromide using sunlight is an example of this type of reaction.

9. Q9Hard

   What is the balanced equation for the reaction of iron with water to form iron(III) oxide and hydrogen gas?

   • A.Fe(s) + H2O(l) → Fe3O4(s) + H2(g)
   • B.3Fe(s) + 4H2O(l) → Fe3O4(s) + 4H2(g)
   • C.Fe(s) + 4H2O(l) → Fe3O4(s) + 2H2(g)
   • D.3Fe(s) + 2H2O(l) → Fe3O4(s) + 3H2(g)
   Answer: 3Fe(s) + 4H2O(l) → Fe3O4(s) + 4H2(g)

   Explanation: Balancing chemical equations ensures the conservation of mass. This equation is balanced by adjusting the number of atoms of each element on both sides.

10. Q10Hard

    What is the role of sunlight in the reaction: 2AgBr(s) → 2Ag(s) + Br2(g)?

    • A.Catalyst
    • B.Reactant
    • C.Energy source for endothermic reaction
    • D.Inhibitor
    Answer: Energy source for endothermic reaction

    Explanation: Sunlight provides the energy required to break the bonds in silver bromide, making it an endothermic reaction.

11. Q11Hard

    What is the balanced equation for the reaction of zinc with silver nitrate?

    • A.Zn(s) + AgNO3(aq) → Zn(NO3)2(aq) + Ag(s)
    • B.Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2Ag(s)
    • C.Zn(s) + AgNO3(aq) → ZnNO3(aq) + Ag(s)
    • D.Zn(s) + 2AgNO3(aq) → ZnNO3(aq) + 2Ag(s)
    Answer: Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2Ag(s)

    Explanation: Balancing this equation ensures that the number of atoms for each element is the same on both sides of the equation.

12. Q12Hard

    What is the correct balanced equation for the reaction between iron and water to form iron(III) oxide and hydrogen gas? (a) Fe(s) + H₂O(l) → Fe₂O₃(s) + H₂(g) (b) 3Fe(s) + 4H₂O(l) → Fe₃O₄(s) + 4H₂(g) (c) 4Fe(s) + 3H₂O(l) → 2Fe₂O₃(s) + 6H₂(g) (d) Fe(s) + 2H₂O(l) → FeO(s) + 2H₂(g)

    • A.(a) Fe(s) + H₂O(l) → Fe₂O₃(s) + H₂(g)
    • B.(b) 3Fe(s) + 4H₂O(l) → Fe₃O₄(s) + 4H₂(g)
    • C.(c) 4Fe(s) + 3H₂O(l) → 2Fe₂O₃(s) + 6H₂(g)
    • D.(d) Fe(s) + 2H₂O(l) → FeO(s) + 2H₂(g)
    Answer: (b) 3Fe(s) + 4H₂O(l) → Fe₃O₄(s) + 4H₂(g)

    Explanation: This equation is balanced with respect to the number of atoms of each element on both sides of the reaction.

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