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Materials and Matter - Changing states: Melting and Freezing

Grade 3IGCSE

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

🔑Concepts

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Matter can change between different states, such as solid and liquid, by adding or removing heat energy.

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Melting is the process where a solid changes into a liquid. This occurs when the temperature increases (heating).

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Freezing is the process where a liquid changes into a solid. This occurs when the temperature decreases (cooling).

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For water (H2OH_2O), the temperature at which it freezes or ice melts is 0∘C0^\circ C.

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Melting and freezing are physical changes that are usually reversible, meaning we can change the substance back to its original state.

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In a solid, particles are packed closely together. When heat is added, they move more until they slide past each other as a liquid.

📐Formulae

Solid+Heat→LiquidSolid + Heat \rightarrow Liquid

Liquid−Heat→SolidLiquid - Heat \rightarrow Solid

Melting Point of H2O=0∘CMelting\ Point\ of\ H_2O = 0^\circ C

Freezing Point of H2O=0∘CFreezing\ Point\ of\ H_2O = 0^\circ C

💡Examples

Problem 1:

Sarah puts a plastic bottle of water into the freezer. After 4 hours, the water has turned into ice. What is this process called, and what happened to the heat?

Solution:

This process is called freezing.

Explanation:

Heat was removed from the liquid water by the freezer. When the temperature of the H2OH_2O reached 0∘C0^\circ C, it changed state from a liquid to a solid.

Problem 2:

An ice cube is placed on a warm plate. Over time, a puddle of water forms. Identify the change of state.

Solution:

Solid→LiquidSolid \rightarrow Liquid (Melting)

Explanation:

The ice cube absorbs heat from the warm plate and the surrounding air. This causes the particles to move faster and break away from their fixed positions, turning the solid ice into liquid water.

Problem 3:

If you have 50g50g of liquid chocolate and you freeze it into a solid bar, how much will the solid bar weigh?

Solution:

50g50g

Explanation:

During a change of state like freezing, the mass of the material stays the same even though its appearance changes.