Questions on Chemical Reactions
Multiple-Choice Questions – Chemical Reactions
1. What is a chemical reaction?
A) A physical change in a substance
B) A change in the state of matter
C) A process where substances are rearranged to form new substances
D) A change in the size or shape of a substance
E) A mixture of elements and compounds
2. Which of the following is a sign of a chemical reaction?
A) Dissolving sugar in water
B) Melting ice
C) Formation of a gas
D) Breaking glass
E) Cutting paper
3. What is formed as a result of a chemical reaction?
A) The same substances
B) Physical mixtures
C) New substances
D) Separated atoms only
E) Only gases
4. The substances present before a chemical reaction are called:
A) Products
B) Catalysts
C) Reactants
D) Ions
E) Enzymes
5. The substances produced in a chemical reaction are called:
A) Reactants
B) Molecules
C) Catalysts
D) Products
E) Atoms
6. Which of the following represents a chemical reaction?
A) H₂O (liquid) → H₂O (gas)
B) CO₂ + H₂O → H₂CO₃
C) Salt dissolving in water
D) Ice melting
E) Water boiling
7. What is the role of a catalyst in a chemical reaction?
A) Increases temperature
B) Slows down the reaction
C) Speeds up the reaction without being consumed
D) Becomes part of the product
E) Changes color during reaction
8. Which of these is an example of a chemical change?
A) Ice melting
B) Water boiling
C) Iron rusting
D) Glass breaking
E) Dissolving sugar
9. A precipitate in a chemical reaction is:
A) A gas
B) A colorless solution
C) A solid formed from two solutions
D) A type of energy
E) An acid
10. Which type of reaction is this: A + B → AB?
A) Decomposition
B) Single replacement
C) Synthesis
D) Combustion
E) Neutralization
11. Which type of reaction is this: AB → A + B?
A) Synthesis
B) Combustion
C) Double replacement
D) Decomposition
E) Displacement
12. What happens to atoms during a chemical reaction?
A) They disappear
B) They change into light
C) They rearrange to form new substances
D) They become energy
E) They increase in size
13. Which law states that mass is conserved during a chemical reaction?
A) Law of Conservation of Energy
B) Law of Thermodynamics
C) Law of Constant Proportions
D) Law of Conservation of Mass
E) Law of Gravity
14. Which is an example of a combustion reaction?
A) Boiling water
B) Burning wood
C) Melting wax
D) Evaporating alcohol
E) Mixing salt and water
15. The burning of fuel typically produces:
A) Only oxygen
B) Heat and light
C) Ice and gas
D) Water and sugar
E) Electricity directly
16. In a chemical reaction, energy is usually:
A) Ignored
B) Created from nothing
C) Absorbed or released
D) Destroyed
E) Not involved
17. What is a balanced chemical equation?
A) Reactants equal products by appearance
B) Same number of atoms of each element on both sides
C) Same size of molecules
D) Equal amounts of energy used
E) Same number of molecules
18. Which reaction type involves two compounds exchanging parts?
A) Synthesis
B) Single replacement
C) Combustion
D) Double replacement
E) Decomposition
19. Which of the following does not represent a chemical change?
A) Baking a cake
B) Digesting food
C) Rusting iron
D) Melting ice
E) Burning paper
20. A chemical reaction that absorbs heat is called:
A) Exothermic
B) Combustion
C) Endothermic
D) Isothermal
E) Neutralization
21. A chemical reaction that releases heat is:
A) Endothermic
B) Exothermic
C) Catalytic
D) Photochemical
E) Diluted
22. What is required for most reactions to begin?
A) Gas
B) Light
C) Heat or activation energy
D) Cold temperature
E) Magnetic fields
23. The rate of a chemical reaction can be increased by:
A) Lowering the temperature
B) Decreasing the concentration
C) Adding a catalyst
D) Reducing surface area
E) Freezing the reactants
24. When a candle burns, which part is a chemical reaction?
A) Melting wax
B) Evaporating water
C) Wax burning into gases
D) Wax dripping
E) Wick turning white
25. What best describes a neutralization reaction?
A) Acid + Water → Base
B) Acid + Base → Salt + Water
C) Base + Water → Acid
D) Salt + Water → Acid
E) Acid + Gas → Water
26. A color change during a reaction usually indicates:
A) Light reflection
B) Physical change
C) Chemical reaction
D) Freezing point change
E) No change
27. Which is an example of energy being released in a reaction?
A) Photosynthesis
B) Boiling
C) Fireworks exploding
D) Ice melting
E) Salt dissolving
28. Which of the following occurs in all chemical reactions?
A) Gas production
B) Light release
C) New substances form
D) Color change
E) Phase change
29. What is the purpose of using chemical equations?
A) To list the color of substances
B) To show how much a substance costs
C) To represent chemical reactions
D) To mix ingredients
E) To label lab equipment
30. In a chemical reaction, the total number of each type of atom:
A) Increases
B) Decreases
C) Remains the same
D) Doubles
E) Changes randomly
- Questions on Mixtures, Homogeneous and Heterogeneous Mixtures
- Questions on Separating Mixtures
- Questions on Elements and Compounds
Answer Key with Explanations
1. C) Chemical reactions create new substances by rearranging atoms.
2. C) Formation of a gas is a sign of a chemical change.
3. C) New substances are formed during a chemical reaction.
4. C) Reactants are the starting materials in a chemical reaction.
5. D) Products are the new substances formed after a reaction.
6. B) CO₂ + H₂O → H₂CO₃ is a chemical reaction (new substance formed).
7. C) Catalysts speed up reactions without being consumed.
8. C) Rusting is a chemical change (new substance formed).
9. C) A precipitate is a solid formed from mixing two solutions.
10. C) A + B → AB is a synthesis reaction.
11. D) AB → A + B is a decomposition reaction.
12. C) Atoms rearrange to form new substances in reactions.
13. D) The Law of Conservation of Mass says mass is neither created nor destroyed.
14. B) Burning wood is a combustion reaction.
15. B) Combustion produces heat and light.
16. C) Chemical reactions involve energy being absorbed or released.
17. B) A balanced equation has equal atoms on both sides.
18. D) Double replacement involves exchange of ions between compounds.
19. D) Melting ice is a physical change, not a chemical one.
20. C) Endothermic reactions absorb heat.
21. B) Exothermic reactions release heat.
22. C) Activation energy (often in the form of heat) is needed to start a reaction.
23. C) Catalysts increase the rate of reaction.
24. C) Burning wax is a chemical change (gas formation and new substances).
25. B) Neutralization: acid + base → salt + water.
26. C) Color change is a clue a chemical reaction has occurred.
27. C) Fireworks release energy in the form of heat, sound, and light.
28. C) All chemical reactions form new substances.
29. C) Chemical equations represent what happens during a reaction.
30. C) The total number of atoms remains the same (conservation of mass).
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