Chemical Reactions and Equations
NCERT-aligned YTC learning page covering core concepts, equation writing and balancing, reaction types, oxidation-reduction, corrosion and rancidity, followed by guided practice and exam preparation.
Chapter Concepts
1. Chemical Reactions
A chemical reaction changes one or more substances into new substances. Common observations include change in colour or temperature, gas formation and formation of a precipitate.
2. Chemical Equations
Chemical equations represent reactions using symbols and formulae. A balanced equation has the same number of atoms of every element on both sides.
3. Types of Reactions
- Combination
- Decomposition
- Displacement
- Double displacement
- Oxidation and reduction
4. Everyday Effects
Corrosion is the gradual damage of metals through chemical reaction with the environment. Rancidity involves oxidation that spoils fats and oils.
Worked Learning Examples
Use these original examples to practise equation interpretation and balancing.
Magnesium combines with oxygen to form magnesium oxide. The equation is balanced because both sides contain two Mg atoms and two O atoms.
Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated.
Zinc displaces copper from copper sulphate; this illustrates a displacement reaction.
Exercise & Step-by-Step Practice
Practice 1
Balance: H₂ + O₂ → H₂O
Solution: Put coefficient 2 before H₂O, then coefficient 2 before H₂.
Practice 2
Identify the reaction type: CaO + H₂O → Ca(OH)₂
Solution: Two reactants form one product, so it is a combination reaction.
Practice 3
Why should a chemical equation be balanced?
Solution: Balancing represents conservation of mass by keeping the number of atoms of each element equal on both sides.
Practice 4
Give one method to slow rancidity.
Solution: Reducing exposure to oxygen—for example through airtight storage—can slow oxidation of fats and oils.
NCERT exercise support: YTC solutions are independently written. Students should use their current NCERT textbook question/exercise numbers alongside these explanations rather than treating this page as a reproduction of the textbook.
Important Questions & Exam Practice
- What observations can indicate that a chemical reaction has occurred?
- Differentiate combination and decomposition reactions with examples.
- Explain oxidation and reduction in a reaction.
- Why is corrosion undesirable? State practical prevention methods.
- Explain rancidity and methods used to reduce it.
PYQ / Test Zone
Board-style and official-paper-based questions will be mapped by year only after source verification. No question is labelled as a CBSE PYQ unless its source is verified.
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