Class notes science class 10th DIGI SMART BOOKS Understanding NCERT Science for Class 10

Q . NO 1: Define combination, decomposition, displacement, and double
displacement reactions with two examples?

ANS: Combination reactions involve reactants combining to form a single
product, while decomposition reactions break down a single reactant into
multiple products. Displacement reactions occur when a more reactive
element replaces a less reactive one in a compound. In double
displacement reactions, ions are exchanged between two compounds to
form two new compounds.

Combination Reaction

 Definition: Two or more substances combine to form a single
product.

 Example 1: The formation of water from hydrogen and oxygen:
2 H 2 (g)+O2 ( g)→2 H 2 O(l )

 Example 2: The formation of iron sulfide from iron and sulfur:
Fe(s)+ S(s) → FeS(s)



Decomposition Reaction

 Definition: A single compound breaks down into two or more
simpler substances.

 Example 1: The breakdown of calcium carbonate when heated to
produce calcium oxide and carbon dioxide:

CaC O3 (s )heatCaO( s)+C O2 (g)

 Example 2: The electrolysis of water to produce hydrogen and
oxygen: 2 H 2 O(l) electricity 2 H 2(g)+O 2 (g)



Displacement Reaction

 Definition: A more reactive element displaces a less reactive
element from its compound.

 Example 1: Iron displaces copper from copper sulfate solution:
Fe(s)+CuS O4 (aq)→ FeS O4 (aq)+Cu( s)

 Example 2: Zinc displaces copper from copper sulfate solution:
Zn(s )+CuS O 4 (aq)→ ZnS O 4 (aq)+ Cu( s)



Double Displacement Reaction

,  Definition: Two compounds in solution react, and their ions are
exchanged to form two new compounds.

 Example 1: Sodium hydroxide reacts with hydrochloric acid, with a
double displacement occurring to form sodium chloride and water:
NaOH (aq)+ HCl (aq)→ NaCl( aq)+ H 2 O(l)

 Example 2: Silver nitrate reacts with sodium chloride to form silver
chloride precipitate and sodium nitrate:
AgN O 3 ( aq)+ NaCl (aq) → AgCl(s)+ NaN O 3 ( aq)

Q .NO 2: Define corrosion and rancidity with preventions?

ANS: Corrosion is the gradual destruction of metals by chemical or electrochemical
reaction with their environment, while rancidity is the spoilage of fats and oils in food
due to oxidation. Both can be prevented through various methods: corrosion prevention
includes coating metals with paint or zinc (galvanization), and rancidity prevention
involves storing food in airtight containers, adding antioxidants, and using inert gases
like nitrogen.

Corrosion

 Definition: The natural process where a refined metal is slowly destroyed and
converted into a more stable oxide due to reactions with its environment, such as
air, moisture, or chemicals.

 Example: Iron reacting with oxygen and water to form rust.

 Prevention:

o Applying protective coatings like paint or oil.

o Galvanization: Coating iron with a layer of zinc.

o Using corrosion inhibitors.

o Alloying metals to improve resistance.

Rancidity

 Definition: The spoilage of food containing fats and oils, which leads to an
unpleasant smell and taste due to oxidation when exposed to air.

 Example: Chips or butter becoming stale when left open.

 Prevention:

o Storing food in airtight containers to limit air exposure.

o Adding antioxidants to the food.