1. What is a chemical reaction? Give an example.
A chemical reaction is a process where one or more substances, called reactants, are converted to one or more different substances, called products. Example: The rusting of iron (4Fe + 3O₂ + 2H₂O → 4Fe(OH)₃).
2. What is the law of conservation of mass?
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.
3. Differentiate between physical and chemical changes.
Physical changes are changes in the physical state of a substance without altering its chemical composition (e.g., melting ice). Chemical changes result in the formation of new substances (e.g., burning wood).
4. What are reactants and products in a chemical reaction?
Reactants are the starting substances in a chemical reaction, while products are the substances formed as a result of the reaction.
5. Give an example of a balanced chemical equation.
Example: 2H₂ + O₂ → 2H₂O is a balanced chemical equation as the number of atoms of each element is the same on both sides.
6. What is the significance of a catalyst in a chemical reaction?
A catalyst is a substance that speeds up a chemical reaction without being consumed itself. It lowers the activation energy required for the reaction.
7. Explain the term ‘exothermic reaction’ with an example.
An exothermic reaction is a chemical reaction that releases heat. Example: Combustion of fuels like wood or coal releases heat energy.
8. What is a decomposition reaction? Give an example.
A decomposition reaction is a reaction where a single compound breaks down into two or more products. Example: 2H₂O → 2H₂ + O₂.
9. Define oxidation and reduction in terms of oxygen transfer.
Oxidation is the process of gaining oxygen or losing hydrogen, while reduction is the process of losing oxygen or gaining hydrogen.
10. Describe the method to balance a chemical equation.
To balance a chemical equation, count the number of atoms of each element in the reactants and products. Adjust the coefficients to make them equal on both sides while keeping the smallest whole numbers.
1. In a chemical equation, the substances that combine or react with each other are called ______.
Answer: reactants
2. The substance formed as a result of a chemical reaction is called ______.
Answer: product
3. A reaction that absorbs energy is called ______.
Answer: endothermic
4. A balanced chemical equation has the same number of atoms of ______ in the reactants and products.
Answer: each element
5. The symbol that indicates a chemical change is ______.
Answer: →
6. The process of combining two or more substances to form a new substance is called ______.
Answer: synthesis
7. The chemical formula of water is ______.
Answer: H₂O
8. The addition of oxygen to a substance is called ______.
Answer: oxidation
9. When a substance burns in air, it undergoes a ______ reaction.
Answer: combustion
10. A substance that increases the rate of a chemical reaction is called a ______.
Answer: catalyst
1. Which of the following is an example of a physical change?
a) Rusting of iron
b) Burning of paper
c) Melting of ice
d) Cooking of food
Answer: c) Melting of ice
2. Which of the following indicates a chemical reaction has occurred?
a) Change in color
b) Gas production
c) Formation of a precipitate
d) All of the above
Answer: d) All of the above
3. What is the main purpose of balancing a chemical equation?
a) To make it look neat
b) To obey the law of conservation of mass
c) To ensure the products are pure
d) To reduce the number of reactants
Answer: b) To obey the law of conservation of mass
4. What does the symbol ‘Δ’ indicate in a chemical equation?
a) Temperature change
b) Catalyst used
c) Pressure application
d) Heating
Answer: d) Heating
5. Which of the following is a characteristic of a chemical change?
a) Change in state
b) Reversibility
c) Formation of new substances
d) No change in energy
Answer: c) Formation of new substances
6. The following reaction is an example of which reaction type: 2Na + Cl₂ → 2NaCl?
a) Decomposition
b) Combination
c) Displacement
d) Redox
Answer: b) Combination
7. Which of the following does not affect the rate of a chemical reaction?
a) Temperature
b) Surface area
c) Pressure
d) Color of reactants
Answer: d) Color of reactants
8. When an acid reacts with a base, the products formed are known as:
a) Salt and water
b) Hydrogen gas
c) Carbon dioxide
d) Hydrocarbon
Answer: a) Salt and water
9. What type of reaction is represented by the equation: AgNO₃ + NaCl → AgCl + NaNO₃?
a) Combination
b) Decomposition
c) Redox
d) Double displacement
Answer: d) Double displacement
10. Which of the following is NOT a characteristic of a chemical change?
a) Release of gas
b) Change in color
c) Change in physical properties
d) Formation of a precipitate
Answer: c) Change in physical properties
1. (2019) Write a balanced chemical equation for the following reaction:
Zinc carbonate is heated to form zinc oxide and carbon dioxide.
Answer: ZnCO₃ → ZnO + CO₂
2. (2020) What type of chemical reaction is represented by the digestion of food in our body?
Answer: The digestion of food in our body is primarily a decomposition reaction, where complex molecules are broken down into simpler ones.
3. (2021) Balance the following chemical equation:
__Al + __H₂SO₄ → __Al₂(SO₄)₃ + __H₂
Answer: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂
4. (2022) What is a redox reaction? Give an example.
Answer: A redox reaction is a chemical reaction in which the oxidation states of atoms are changed. Example: The reaction between zinc and copper sulfate (Zn + CuSO₄ → ZnSO₄ + Cu) is a redox reaction.
5. (2023) Explain the term ‘corrosion’ and give one method to prevent it.
Answer: Corrosion is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. One method to prevent corrosion is galvanization, where a protective zinc coating is applied to steel or iron.