Physical Change

Understanding how matter changes form while maintaining its chemical identity

CAPS Grade 10 Physical Sciences

Physical change occurs when matter changes form but not chemical composition. The molecules remain exactly the same—only their arrangement, state, or appearance changes.

1. Definition and Characteristics

No New Substances

The chemical composition remains exactly the same before and after the change.

Example: Ice (H₂O) → Water (H₂O)

→

H₂O molecules remain unchanged

Reversibility

Physical changes are typically reversible—the original state can be restored.

Example: Water → Ice → Water

↔️

Small Energy Changes

Energy changes are relatively small compared to chemical reactions.

Ice melting: Absorbs heat

Small energy input

Quick Check

Which of the following is NOT a characteristic of physical change?

2. Molecular Level View

What happens to particles?

Solid (Ice)

Particles are tightly packed in fixed positions. They vibrate but don't move past each other.

Liquid (Water)

Particles are close but can slide past each other. They have more energy and move freely.

Intermolecular Forces: During physical changes, only the forces BETWEEN molecules change. The bonds WITHIN molecules (intramolecular bonds) remain intact.

Interactive Molecular Viewer

Click to see how particle arrangement changes during phase changes:

3. Types of Physical Changes

Phase Changes (Changes of State)

Solid

↔️

Liquid

↔️

Gas

Melting and Freezing

Melting Solid → Liquid (absorbs heat)

Freezing Liquid → Solid (releases heat)

H₂O(s) ⇌ H₂O(l)

Evaporation and Condensation

Evaporation Liquid → Gas (absorbs heat)

Condensation Gas → Liquid (releases heat)

H₂O(l) ⇌ H₂O(g)

Sublimation and Deposition

Sublimation Solid → Gas (absorbs heat)

Deposition Gas → Solid (releases heat)

CO₂(s) → CO₂(g) (dry ice)

Dissolving

Solute disperses in solvent without changing chemical identity.

Sugar + Water → Sugar solution

C₁₂H₂₂O₁₁(s) → C₁₂H₂₂O₁₁(aq)

Mechanical Changes

Crushing

Breaking a solid into smaller pieces

Tearing

Separating material into parts

Grinding

Reducing to powder

Sort the Changes

Click each item to sort it into the correct category:

Phase Change

Mechanical Change

Ice melting Crushing a can Water boiling Tearing paper Dry ice subliming Grinding chalk

4. Conservation Laws

Conservation of Mass

Total mass remains constant before and after a physical change.

Example: 100g ice → 100g water

100g → 100g

Conservation of Atoms

Number and type of atoms remain unchanged.

H₂O (ice) → H₂O (water)

2 H atoms + 1 O atom on both sides

Conservation of Molecules

Same number of molecules before and after.

100 H₂O molecules (ice)

→ 100 H₂O molecules (water)

Mass Conservation Calculator

If you melt 50g of ice, what mass of water do you get?

g ice → 50 g water

Test Your Understanding

1. Which of the following is a physical change?

Burning wood Rusting iron Melting chocolate Cooking an egg

2. What happens to water molecules when ice melts?

They break apart into hydrogen and oxygen They rearrange but remain H₂O They disappear They combine to form new molecules

Key Terms

Physical change Phase change Intermolecular forces Melting Freezing Evaporation Condensation Sublimation Deposition Dissolving Conservation of mass Kinetic Molecular Theory

Key Takeaways

Physical changes do not form new substances - the chemical composition remains the same
Physical changes are typically reversible
Only intermolecular forces change; intramolecular bonds remain intact
Phase changes (melting, freezing, evaporation, condensation, sublimation, deposition) are physical changes
Dissolving and mechanical changes are also physical changes
Mass, atoms, and molecules are all conserved during physical changes

Physical and Chemical Change Chemical Change