Chemical Reactions and Corrosion
NCERT Class 10 • Science • Chapter "Chemical Reactions and Equations"
Chemical Reactions and Corrosion
A chemical reaction changes reactants into products with different properties. Every reaction is written as a chemical equation, which must be balanced so that the number of atoms of each element is the same on both sides, as required by the law of conservation of mass.
Types of Chemical Reactions
- A combination reaction joins two or more substances into a single product, as when quicklime reacts with water.
- A decomposition reaction breaks one substance into two or more, and may be driven by heat, light or electricity.
- A displacement reaction occurs when a more reactive element takes the place of a less reactive one in a compound.
- A double displacement reaction exchanges ions between two compounds, often forming a precipitate.
- An exothermic reaction releases heat, as in respiration and combustion; an endothermic reaction absorbs heat.
- Oxidation is the gain of oxygen or loss of hydrogen; reduction is the loss of oxygen or gain of hydrogen.
- A reaction in which both occur together is called a redox reaction, and one substance is the oxidising and the other the reducing agent.
Corrosion and Rancidity
- Corrosion is the slow damage to a metal surface by air, moisture or chemicals around it.
- Rusting of iron is the most familiar example; copper turns green and silver turns black over time.
- Corrosion is prevented by painting, oiling, greasing, galvanising, anodising and by alloying.
- The economic cost of corrosion is very large, since it damages bridges, ships, pipelines, vehicles and machinery.
- Rancidity is the spoiling of fats and oils in food by oxidation, which changes their smell and taste.
- Rancidity is slowed by adding antioxidants, by refrigeration, by keeping food in airtight containers, and by flushing packets with nitrogen.
| Reaction Type | What Happens | Example |
|---|---|---|
| Combination | Two or more give one product | Quicklime and water |
| Decomposition | One gives two or more products | Heating of a carbonate |
| Displacement | More reactive replaces less reactive | Iron in copper sulphate |
| Double displacement | Ions exchange, precipitate forms | Barium chloride and sodium sulphate |
Rancidity — the oxidation of fats and oils in food, which changes their smell and taste and makes them unfit to eat.
Exam me kaise aata hai
- Gain of oxygen in a reaction is called — oxidation
- Spoiling of oily food by oxidation is called — rancidity
- Which gas is filled in food packets to prevent rancidity — nitrogen
- A reaction that releases heat is called — exothermic
UPSC/State PSC ke liye
- Nitrogen is used in food packets because it is unreactive, so it displaces oxygen without itself reacting with the food.
- Balancing an equation is not a formality; it enforces the law of conservation of mass, which is why atoms can be rearranged but never created or destroyed.
Yahan confuse hote hain
✗ Oxidation always means adding oxygen | It also includes the loss of hydrogen | ✓
✗ Corrosion and rancidity are the same | Corrosion affects metals; rancidity affects fats and oils | ✓
✗ An exothermic reaction absorbs heat | It releases heat; endothermic absorbs it | ✓
Ek nazar me
- Equations must be balanced to satisfy conservation of mass.
- Types: combination, decomposition, displacement and double displacement.
- Oxidation gains oxygen or loses hydrogen; reduction is the reverse.
- Corrosion damages metals; rancidity spoils fats and is slowed by antioxidants and nitrogen.
Ab practice karein
Acids, bases aur metals se har exam me seedhe questions bante hain. ExamAtlas ke mock test se abhi practice karein.