Changes Around Us Physical and Chemical Class 7 Notes

Changes Around Us Physical and Chemical Class 7 Notes

Changes Around Us Physical and Chemical Class 7 Notes

1. Inflate: Increase (something) by a large or excessive amount.
2. Chemical reaction: The processes by which chemicals interact to form new chemical substances with different compositions.
3. Chemical equation: A way to represent a chemical reaction using element symbols or names.
4. Infer: To deduce or conclude something from evidence.
5. Combustion: A chemical reaction in which a substance reacts with oxygen and produces heat and/or light.
6. Extinguished: To put out a fire, flame or light, etc.
7. Fireflies: Insects emitting light in late evenings.
8. Bioluminescence: The production of light in living organisms.
9. Magnifying glass: A special glass used to make an object look larger than it is.
10. Ignition temperature: Minimum temperature at which a substance catches fire.
11. Vapourisation: The process where a liquid or solid substance changes into a gaseous state, or vapour.
12. Reversed: To change the direction, order, position, result, etc.
13. Desirable: Having good or pleasing qualities.
14. Weathering: The physical and chemical changes in rocks.
15. Erosion: When rock pebbles, soil, and sediments are broken down and moved from one location to another by natural forces like wind and flowing water.
16. Exothermic: To give off heat.

Types of Changes:

1. Physical Changes and Chemical Changes

Physical Changes:

1. Definition: Changes in which only physical properties like shape, size, and state of substances change.
2. Characteristics: Usually reversible, involve changes in size, shape, or state.
3. Examples: Melting of ice, boiling water, cutting paper, folding a handkerchief.

Chemical Changes:

1. Definition: Changes in which one or more new substances are formed.
2. Characteristics: Usually irreversible, involve chemical reactions.
3. Examples: Rusting of iron (formation of iron oxide), combustion of magnesium (formation of magnesium oxide).

Rusting:

1. Process: Iron reacts with air (oxygen) and moisture to form rust (iron oxide).
2. Significance: A common example of a chemical change that can weaken the structures.
3. Combustion: Heat and/or light.
4. Example: Burning of magnesium ribbon to form magnesium oxide.
5. Requirements for combustion: A combustible substance (fuel), Oxygen and ignition temperature

Physical vs. Chemical Changes:

Physical Changes:

1. Do not produce new substances.
2. Examples: Melting, freezing, dissolving.
3. Chemical Changes: Produce new substances.
4. Examples: Rusting, burning, decomposition.

Ignition Temperature:

1. Definition: The minimum temperature at which a substance catches fire.
2. Importance: Understanding ignition temperature helps in fire safety and combustion processes.
3. Slow Natural Changes: Examples of natural processes that involve physical and chemical changes, such as soil formation from rocks due to weathering and Erosion.

Comparisons

1. Physical: No new substance formed
2. Chemical: New substance formed

Additional Concepts:

Rusting

Iron + Oxygen + Moisture → Rust (Iron Oxide) Weakens structures

Combustion

1. Burning of substances → Heat and/or Light
2. Example: Magnesium ribbon ⟶ Magnesium Oxide

→ Requirements:

Fuel (combustible substance)

Oxygen

Ignition temperature

→ Ignition Temperature

Minimum temperature needed to start combustion

Important for fire safety

→ Slow Natural Changes

Weathering of rocks into soil

Involve both physical and chemical changes

Soil erosion