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Matter and Materials - Change of state (Melting, Vaporization, Condensation, Freezing)

Grade 5ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Matter can change from one state to another (Solid, Liquid, Gas) by heating or cooling.

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Melting (Fusion): The process of changing a SolidSolid into a LiquidLiquid state on heating. For example, Ice changing to water at 0∘C0^{\circ}C.

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Vaporization (Boiling): The process of changing a LiquidLiquid into a GasGas (vapor) state on heating. Water boils at 100∘C100^{\circ}C.

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Condensation: The process of changing a GasGas into a LiquidLiquid state on cooling. This is the reverse of vaporization.

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Freezing (Solidification): The process of changing a LiquidLiquid into a SolidSolid state on cooling. Water freezes into ice at 0∘C0^{\circ}C.

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During these processes, the temperature of the substance typically remains constant until the change of state is complete.

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The chemical formula for water in all three states (Ice, Water, Steam) remains H2OH_{2}O.

📐Formulae

Solid→HeatLiquid→HeatGasSolid \xrightarrow{Heat} Liquid \xrightarrow{Heat} Gas

Gas→CoolLiquid→CoolSolidGas \xrightarrow{Cool} Liquid \xrightarrow{Cool} Solid

Melting Point of H2O=0∘C\text{Melting Point of } H_{2}O = 0^{\circ}C

Boiling Point of H2O=100∘C\text{Boiling Point of } H_{2}O = 100^{\circ}C

💡Examples

Problem 1:

Explain what happens to the molecules of ice when it is heated to become water.

Solution:

The process is called MeltingMelting.

Explanation:

When ice (SolidSolid) is heated, the molecules gain energy and start vibrating faster. They overcome the strong forces of attraction holding them in a fixed position and begin to move around, turning the ice into water (LiquidLiquid).

Problem 2:

Why do we see 'steam' coming out of a kettle when water is boiled?

Solution:

Liquid→GasLiquid \rightarrow Gas (Vaporization).

Explanation:

When water is heated to 100∘C100^{\circ}C, it reaches its boiling point. The molecules gain enough energy to escape into the air as water vapor or steam.

Problem 3:

What is the phenomenon where dew drops form on grass during a cold morning?

Solution:

CondensationCondensation.

Explanation:

Water vapor present in the air (Gas) touches the cold surface of the grass. It loses heat energy and changes back into tiny droplets of water (Liquid).