1. Introduction to Chemical Reactions
A chemical reaction is a process in which reactants transform into products.
Example: Rusting of iron
Fe + O₂ + H₂O → Fe₂O₃ . xH₂O
2. Chemical Equations
A chemical equation represents a reaction using symbols.
Example: Magnesium burns in oxygen
Mg + O₂ → MgO
Balanced vs. Unbalanced Equations
Unbalanced: H₂ + O₂ → H₂O
Balanced: 2H₂ + O₂ → 2H₂O
3. Types of Chemical Reactions
1. Combination Reaction: Two or more reactants combine to form a single product.
CaO + H₂O → Ca(OH)₂
2. Decomposition Reaction: A single reactant breaks down into two or more products.
2H₂O → 2H₂ + O₂
3. Displacement Reaction: A more reactive element displaces a less reactive element.
Zn + CuSO₄ → ZnSO₄ + Cu
4. Double Displacement Reaction: Two compounds exchange ions to form new compounds.
AgNO₃ + NaCl → AgCl + NaNO₃
5. Oxidation and Reduction (Redox) Reaction: Involves the addition/removal of oxygen or hydrogen.
CuO + H₂ → Cu + H₂O
Chemical Equations – Explanation and MCQs
What is a Chemical Equation?
A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants, products, and their relative amounts in a reaction.
Components of a Chemical Equation
✔ Reactants: The substances that take part in the reaction and undergo change.
✔ Products: The substances formed as a result of the reaction.
✔ Arrow ( → ): Indicates the direction of the reaction from reactants to products.
Example of a Chemical Equation
Methane burns in oxygen to form carbon dioxide and water:
CH₄ + 2O₂ → CO₂ + 2H₂O
Types of Chemical Equations
✔ Balanced Chemical Equation: The number of atoms of each element is the same on both sides of the equation.
✔ Unbalanced Chemical Equation: The number of atoms of each element is not equal on both sides of the equation.
✔ Skeleton Equation: An equation that does not indicate the exact number of atoms or molecules involved.
Why is it Important to Balance Chemical Equations?
✔ Ensures the Law of Conservation of Mass is followed.
✔ Helps in understanding the correct proportion of reactants and products.
✔ Important for industrial chemical reactions and laboratory experiments.
Multiple Choice Questions on Chemical Equations
1. What does a chemical equation represent?
A) A mathematical calculation
B) A chemical reaction using symbols and formulas
C) A list of elements
D) A mixture of compounds
Answer: B) A chemical reaction using symbols and formulas
2. What are the substances called that take part in a chemical reaction?
A) Products
B) Reactants
C) Compounds
D) Mixtures
Answer: B) Reactants
3. Which of the following is a correctly balanced chemical equation?
A) H₂ + O₂ → H₂O
B) 2H₂ + O₂ → 2H₂O
C) Na + Cl₂ → NaCl
D) Fe + O₂ → Fe₂O₃
Answer: B) 2H₂ + O₂ → 2H₂O
4. What does the arrow (→) in a chemical equation indicate?
A) Movement of molecules
B) Reaction direction from reactants to products
C) Equal number of atoms
D) The end of a reaction
Answer: B) Reaction direction from reactants to products
5. What is the purpose of balancing a chemical equation?
A) To satisfy the Law of Conservation of Mass
B) To make the equation look symmetrical
C) To change the reactants
D) To increase the number of elements
Answer: A) To satisfy the Law of Conservation of Mass
6. Which of the following is an example of an unbalanced chemical equation?
A) Zn + CuSO₄ → ZnSO₄ + Cu
B) H₂ + O₂ → H₂O
C) C + O₂ → CO₂
D) 2H₂ + O₂ → 2H₂O
Answer: B) H₂ + O₂ → H₂O
7. What is a skeleton equation?
A) An equation that does not show exact numbers of atoms or molecules
B) A balanced equation
C) A complete reaction mechanism
D) A reaction with no products
Answer: A) An equation that does not show exact numbers of atoms or molecules
8. In the reaction CH₄ + O₂ → CO₂ + H₂O, what coefficient should be placed before O₂ to balance the equation?
A) 1
B) 2
C) 3
D) 4
Answer: C) 2
9. What does the Law of Conservation of Mass state?
A) Matter can be created or destroyed
B) Mass remains constant in a chemical reaction
C) Mass changes when reactants form products
D) Energy is always conserved
Answer: B) Mass remains constant in a chemical reaction
10. Which type of chemical equation ensures that atoms are equal on both sides?
A) Skeleton equation
B) Balanced equation
C) Unbalanced equation
D) Random equation