Summary of the Chapter-1-Chemical Reactions and Equations with Key-Points:
- A complete chemical equation symbolically represents the reactants, products, and their physical states.
- A chemical equation must be balanced to ensure that the number of atoms of each element is equal on both the reactant and product sides of the equation. Balancing is essential for all chemical equations.
- In a combination reaction, two or more substances merge to form a single new product.
- Decomposition reactions, the reverse of combination reactions, involve a single substance breaking down into two or more simpler substances.
- Exothermic reactions release heat along with the products, whereas endothermic reactions absorb energy during the process.
- A displacement reaction occurs when one element replaces another element within a compound.
- In double displacement reactions, two different ions or groups of atoms are swapped between compounds.
- Precipitation reactions result in the formation of insoluble salts.
- Chemical reactions may also involve the addition or removal of oxygen or hydrogen.
- Oxidation refers to the gain of oxygen or the loss of hydrogen, while reduction is the loss of oxygen or the gain of hydrogen.
1. What is a chemical reaction?
(a) A process that forms a new physical state
(b) A process where reactants turn into products with a change in chemical properties
(c) A process that changes the appearance of a substance
(d) A physical change that does not alter the chemical composition
Explanation: A chemical reaction involves the transformation of reactants into products with new chemical properties.
2. What is the correct word equation for the reaction of magnesium with oxygen?
(a) Magnesium + Water → Magnesium oxide
(b) Magnesium + Oxygen → Magnesium oxide
(c) Oxygen + Magnesium → Magnesium chloride
(d) Magnesium + Air → Magnesium oxide
Explanation: Magnesium reacts with oxygen to form magnesium oxide.
3. Which observation indicates a chemical reaction has taken place?
(a) Change in state
(b) Change in color
(c) Evolution of gas
(d) All of the above
Explanation: All these observations are indicators of a chemical reaction.
4. What is a balanced chemical equation?
(a) An equation with the same number of molecules on each side
(b) An equation with the same number of atoms of each element on both sides
(c) An equation with the same number of compounds on both sides
(d) None of the above
Explanation: A balanced chemical equation has the same number of atoms of each element on both sides.
5. What is formed when calcium oxide reacts with water?
(a) Calcium carbonate
(b) Calcium hydroxide
(c) Calcium sulfate
(d) Calcium chloride
Explanation: Calcium oxide reacts with water to form calcium hydroxide.
6. What type of reaction is the formation of water from hydrogen and oxygen?
(a) Decomposition
(b) Combination
(c) Displacement
(d) Redox
Explanation: Hydrogen and oxygen combine to form water, which is a combination reaction.
7. Which reaction type involves one reactant breaking down into two or more products?
(a) Combination
(b) Displacement
(c) Decomposition
(d) Redox
Explanation: A decomposition reaction involves a single reactant breaking down into multiple products.
8. What is an exothermic reaction?
(a) A reaction that absorbs heat
(b) A reaction that releases heat
(c) A reaction that occurs without any energy change
(d) A reaction that releases light
Explanation: An exothermic reaction releases heat during the process.
9. What happens when silver chloride is exposed to sunlight?
(a) It turns black
(b) It turns grey
(c) It turns green
(d) It turns yellow
Explanation: Silver chloride decomposes into silver and chlorine when exposed to sunlight, turning grey.
10. Which of the following is a double displacement reaction?
(a) 2Ag + Cl₂ → 2AgCl
(b) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
(c) Zn + H₂SO₄ → ZnSO₄ + H₂
(d) 2H₂ + O₂ → 2H₂O
Explanation: Double displacement reactions involve the exchange of ions between the reactants.
11. What type of reaction is observed when iron is dipped into copper sulfate solution?
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction
Explanation: In a displacement reaction, a more reactive metal displaces a less reactive metal from its compound.
12. Which of the following is a balanced chemical equation for the decomposition of water?
(a) H₂O → H₂ + O₂
(b) 2H₂O → 2H₂ + O₂
(c) 2H₂O → H₂ + O₂
(d) H₂O → 2H₂ + O₂
Explanation: The balanced equation shows the correct number of atoms of each element on both sides.
13. What happens when zinc reacts with dilute sulfuric acid?
(a) Zinc sulfate and water are formed
(b) Zinc sulfate and hydrogen gas are formed
(c) Zinc chloride and hydrogen gas are formed
(d) Zinc oxide and water are formed
Explanation: Zinc reacts with dilute sulfuric acid to produce zinc sulfate and hydrogen gas.
14. Which of the following is an example of a combination reaction?
(a) CaO + H₂O → Ca(OH)₂
(b) 2H₂O → 2H₂ + O₂
(c) Zn + CuSO₄ → ZnSO₄ + Cu
(d) AgCl → Ag + Cl₂
Explanation: A combination reaction occurs when two substances combine to form a single product.
15. Which gas is evolved when lead nitrate is heated?
(a) Nitrogen gas
(b) Oxygen gas
(c) Nitrogen dioxide gas
(d) Sulfur dioxide gas
Explanation: Heating lead nitrate produces nitrogen dioxide, which is a brown gas.
16. What is the color change when ferrous sulfate is heated?
(a) Green to white
(b) White to green
(c) Green to brown
(d) Green to yellow
Explanation: Ferrous sulfate decomposes upon heating, changing from green to brown due to the formation of ferric oxide.
17. In the reaction CuO + H₂ → Cu + H₂O, which substance is oxidized?
(a) Copper
(b) Hydrogen
(c) Copper(II) oxide
(d) Water
Explanation: Hydrogen is oxidized because it gains oxygen to form water.
18. What is produced when barium chloride reacts with sodium sulfate?
(a) Barium sulfate and sodium chloride
(b) Barium nitrate and sodium chloride
(c) Sodium sulfate and barium oxide
(d) Barium chloride and sodium sulfate
Explanation: The reaction between barium chloride and sodium sulfate produces barium sulfate and sodium chloride through a double displacement reaction.
19. What is a precipitation reaction?
(a) A reaction that forms a gas
(b) A reaction that forms a solid product
(c) A reaction that absorbs heat
(d) A reaction that releases heat
Explanation: A precipitation reaction is characterized by the formation of an insoluble solid product from two aqueous solutions.
20. In the reaction Fe + CuSO₄ → FeSO₄ + Cu, which element is displaced?
(a) Iron
(b) Copper
(c) Sulfate
(d) Oxygen
Explanation: Copper is displaced by iron, which is more reactive.
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