States of Matter
Lipi Shorts
CBSE · Class 9 · Science
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States of Matter
Central idea
The same particles can stand shoulder-to-shoulder in a marching block (solid), shuffle past each other in a moving crowd (liquid), or scatter and fly across an empty hall (gas): heat is what loosens their grip on one another.
Central idea
Everything around us is made of matter, and matter is built from extremely tiny particles. These particles are always moving, they have empty spaces between them, and they pull on each other with forces of attraction.
Matter is made of particles
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In a solid the particles are packed closely in a fixed, regular pattern and only vibrate in place, so a solid keeps its shape and volume.
The three states
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Heating a substance gives its particles more energy, so they break free of one another: a solid melts into a liquid at its melting point, and a liquid boils into a gas at its boiling point. Cooling reverses this.
Changing state and latent heat
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A liquid does not have to boil to become vapour. At its surface, the fastest particles can escape into the air at any temperature below the boiling point: this is evaporation.
Evaporation and cooling
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See it in a diagram
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Myth vs truth
✕ Myth
When ice is melting, adding heat makes it get warmer.
✓ Truth
While ice melts the temperature stays at 0 degrees C; the heat supplied is latent heat used to break the forces between particles, not to raise temperature.
Myths vs truth
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Word meanings
matter
anything that has mass and occupies space
melting point
the temperature at which a solid changes into a liquid at normal pressure
boiling point
the temperature at which a liquid changes rapidly into a gas throughout its bulk
latent heat
heat absorbed or released during a change of state without any change in temperature
Word meanings
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Themes & message
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The state of a substance depends on how strongly its particles are held together and how much energy they have.
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Heating and cooling interconvert the states, and changes of state happen at fixed temperatures.
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Latent heat and evaporative cooling show that energy can change state without changing temperature.
Themes & message
Key facts at a glance
Three states
Solid, liquid, gas: set by how strongly particles are held together
Particles
Made of tiny moving particles with spaces between them; they attract each other
Solid to liquid
Melting, at the melting point (ice melts at 0 degrees C)
Key facts at a glance
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