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States of Matter - Physical Changes in Matter

Grade 3IB

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

🔑Concepts

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Matter is anything that has mass and takes up space. It is made of tiny particles that are always moving. In a solid, particles are packed tightly; in a liquid, they can slide past each other; in a gas, they move freely and rapidly.

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A physical change is a change in the state or appearance of matter without changing its chemical identity. For example, H2OH_2O (water) is the same substance whether it is ice, liquid water, or steam.

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States of matter can change by adding or removing thermal energy (heat). Adding heat increases the kinetic energy of particles, while removing heat decreases it.

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Melting is the process of a solid turning into a liquid. For water, this happens at the melting point of 0∘C0^\circ C.

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Freezing is the process of a liquid turning into a solid. This occurs when heat is removed, reaching the freezing point of 0∘C0^\circ C.

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Evaporation occurs when a liquid turns into a gas, such as water turning into water vapor at 100∘C100^\circ C (boiling) or through surface evaporation.

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Condensation is the change from a gas to a liquid. An example is water vapor H2O(g)H_2O_{(g)} touching a cold glass and turning into liquid droplets H2O(l)H_2O_{(l)}.

📐Formulae

Solid+Heat→Liquid (Melting)\text{Solid} + \text{Heat} \rightarrow \text{Liquid (Melting)}

Liquid−Heat→Solid (Freezing)\text{Liquid} - \text{Heat} \rightarrow \text{Solid (Freezing)}

Liquid+Heat→Gas (Evaporation)\text{Liquid} + \text{Heat} \rightarrow \text{Gas (Evaporation)}

Gas−Heat→Liquid (Condensation)\text{Gas} - \text{Heat} \rightarrow \text{Liquid (Condensation)}

Tfreeze=0∘C (for H2O)T_{freeze} = 0^\circ C \text{ (for } H_2O)

Tboil=100∘C (for H2O)T_{boil} = 100^\circ C \text{ (for } H_2O)

💡Examples

Problem 1:

An ice cube (H2O(s)H_2O_{(s)}) is placed in a warm pan. Describe the process and identify the state change.

Solution:

The process is called Melting. The ice cube changes from a solid state to a liquid state (H2O(l)H_2O_{(l)}).

Explanation:

The ice absorbs heat energy from the pan. This causes the particles to vibrate faster until they break free from their rigid structure, turning the solid into a liquid.

Problem 2:

After a hot shower, you notice tiny droplets of water on the mirror. What physical change has occurred?

Solution:

The physical change is Condensation: H2O(g)→H2O(l)H_2O_{(g)} \rightarrow H_2O_{(l)}.

Explanation:

Warm water vapor (gas) in the air touches the cool surface of the mirror. It loses heat energy, causing the particles to slow down and cluster together into liquid droplets.

Problem 3:

If a bowl of water is left in a freezer at −5∘C-5^\circ C, what will happen to the particles?

Solution:

The water will undergo Freezing to become ice (H2O(s)H_2O_{(s)}).

Explanation:

Because −5∘C<0∘C-5^\circ C < 0^\circ C, heat is removed from the water. The particles move slower and slower until they lock into a fixed, regular pattern characteristic of a solid.