Question
How can we distinguish between physical and chemical changes? Provide at least three examples.
✓
Answer
Physical Change:
A change that affects the form or appearance of a substance but does not change its chemical composition.
Chemical Change:
A change that involves the formation of new substances with different chemical compositions and properties.
Examples:
1. Burning Wood (Chemical):
→ Wood reacts with oxygen to produce carbon dioxide, water, ash, and heat.
→ New substances (gases and ash) are formed.
→ You cannot turn the ash and gases back into wood, so it's irreversible.
2.Rusting of Iron (Chemical):
→ Iron reacts with oxygen and moisture to form rust (iron oxide).
→ A new substance (rust) with different properties is formed.
→ It's very difficult to turn rust back into iron.
3. Melting Ice (Physical):
→ Ice (H2O in solid form) changes to water (H2O in liquid form).
→ The chemical composition (H2O)remains the same.
→ You can freeze the water back into ice, so it's reversible.
4.Dissolving Sugar in Water (Physical):
→ Sugar disperses evenly in water.
→ It remains sugar.
→ You can evaporate the water to get the sugar back.
5. Cooking an Egg (Chemical):
→ The egg white and yolk change texture and color when heated.
→ The proteins in the egg undergo a chemical change (denaturation).
→ You cannot uncook an egg to get the original raw egg back.
A change that affects the form or appearance of a substance but does not change its chemical composition.
Chemical Change:
A change that involves the formation of new substances with different chemical compositions and properties.
Examples:
1. Burning Wood (Chemical):
→ Wood reacts with oxygen to produce carbon dioxide, water, ash, and heat.
→ New substances (gases and ash) are formed.
→ You cannot turn the ash and gases back into wood, so it's irreversible.
2.Rusting of Iron (Chemical):
→ Iron reacts with oxygen and moisture to form rust (iron oxide).
→ A new substance (rust) with different properties is formed.
→ It's very difficult to turn rust back into iron.
3. Melting Ice (Physical):
→ Ice (H2O in solid form) changes to water (H2O in liquid form).
→ The chemical composition (H2O)remains the same.
→ You can freeze the water back into ice, so it's reversible.
4.Dissolving Sugar in Water (Physical):
→ Sugar disperses evenly in water.
→ It remains sugar.
→ You can evaporate the water to get the sugar back.
5. Cooking an Egg (Chemical):
→ The egg white and yolk change texture and color when heated.
→ The proteins in the egg undergo a chemical change (denaturation).
→ You cannot uncook an egg to get the original raw egg back.
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