Chemical Reactions Quiz - ICSE Class 8 Science

Free practice quiz: Chemical Reactions (ICSE Class 8 Science). 50 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following describes an exothermic reaction?

   1. A reaction that absorbs heat from the surroundings.
   2. A reaction that releases heat into the surroundings.
   3. A reaction that involves the transfer of electrons.
   4. A reaction that forms a precipitate.
   Show answer

   Answer: B. A reaction that releases heat into the surroundings.

   Exothermic reactions are chemical reactions that emit energy, usually in the form of heat, light, or sound. Endothermic reactions, on the other hand, absorb heat from the surroundings.

2. Which of the following is a characteristic of a reversible reaction?

   1. It proceeds to completion, forming only products.
   2. It can proceed in both forward and backward directions.
   3. It always releases energy.
   4. It requires a catalyst to occur.
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   Answer: B. It can proceed in both forward and backward directions.

   Reversible reactions are reactions that can occur in both the forward (reactants to products) and backward (products to reactants) directions. They reach a state of equilibrium where the rates of the forward and reverse reactions are equal.

3. What is the primary role of enzymes in biological chemical reactions?

   1. To increase the activation energy.
   2. To provide energy for the reaction.
   3. To act as catalysts, speeding up reactions.
   4. To bind to reactants permanently.
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   Answer: C. To act as catalysts, speeding up reactions.

   Enzymes are biological catalysts, which are proteins that speed up specific chemical reactions in living organisms by lowering the activation energy required for the reaction to occur.

4. When zinc reacts with dilute sulfuric acid, the products are zinc sulfate and hydrogen gas. This is an example of a:

   1. Combination reaction
   2. Decomposition reaction
   3. Single displacement reaction
   4. Neutralization reaction
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   Answer: C. Single displacement reaction

   The reaction Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g) shows that zinc (a metal) displaces hydrogen (from the acid) to form zinc sulfate and hydrogen gas. This is characteristic of a single displacement reaction.

5. What is the primary product when copper reacts with excess oxygen at high temperatures?

   1. Copper (I) oxide (Cu₂O)
   2. Copper (II) oxide (CuO)
   3. Copper sulfate (CuSO₄)
   4. Copper chloride (CuCl₂)
   Show answer

   Answer: B. Copper (II) oxide (CuO)

   Copper reacts with oxygen at high temperatures to form copper(II) oxide. The reaction is $2Cu(s) + O_2(g) ightarrow 2CuO(s)$. Copper(I) oxide is formed under different conditions.

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