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CIE iGCSE Co-ordinated Sciences-C6.1 Physical and chemical changes- Study Notes- New Syllabus

CIE iGCSE Co-ordinated Sciences-C6.1 Physical and chemical changes – Study Notes

CIE iGCSE Co-ordinated Sciences-C6.1 Physical and chemical changes – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.

Key Concepts:

CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics

Physical and Chemical Changes

Chemical and physical changes describe how substances are transformed. Understanding the differences helps identify whether a chemical reaction has occurred or if it is simply a change of state or form.

Physical Changes:

  • No new substances are formed.
  • Usually reversible (e.g., melting, freezing, boiling, dissolving).
  • Change is in form, size, or state, not in chemical composition.
  • Energy changes are usually small.
  • Examples:
    • Ice melting: \( \text{H}_2\text{O (s)} \rightarrow \text{H}_2\text{O (l)} \)
    • Boiling water: \( \text{H}_2\text{O (l)} \rightarrow \text{H}_2\text{O (g)} \)
    • Dissolving sugar in water: \( \text{C}_{12}\text{H}_{22}\text{O}_{11} \text{(s)} \rightarrow \text{C}_{12}\text{H}_{22}\text{O}_{11} \text{(aq)} \)
    • Breaking glass: \( \text{SiO}_2 \) remains chemically unchanged
    • Freezing water: \( \text{H}_2\text{O (l)} \rightarrow \text{H}_2\text{O (s)} \)

Chemical Changes:

  • Produce one or more new substances with different chemical properties.
  • Usually irreversible under normal conditions.
  • Involves breaking old bonds and forming new bonds.
  • Energy changes can be significant (exothermic or endothermic).
  • Examples:
    • Combustion of methane: \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \)
    • Rusting of iron: \( 4\text{Fe} + 3\text{O}_2 + 6\text{H}_2\text{O} \rightarrow 4\text{Fe(OH)}_3 \)
    • Vinegar reacting with baking soda: \( \text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{NaCH}_3\text{COO} \)
    • Cooking an egg – proteins denature and new substances form
    • Photosynthesis: \( 6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \)
    • Burning paper – new substances like ash, $\text{CO}_2$, and $\text{H}_2\text{O}$ are formed

Key Differences:

  • Physical change: no new substances; chemical change: new substances formed.
  • Physical change: usually reversible; chemical change: usually irreversible.
  • Physical change: small energy change; chemical change: may release or absorb significant energy.

Example 

Classify the following changes as physical or chemical and justify your answer:

  • Melting butter
  • Burning candle
  • Dissolving salt in water
  • Cooking an egg
  • Rusting of iron
  • Boiling water
▶️ Answer/Explanation
  • Melting butter: Physical – changes state from solid to liquid, reversible.
  • Burning candle: Chemical – wax reacts with oxygen to form carbon dioxide and water, irreversible.
  • Dissolving salt in water: Physical – salt remains chemically unchanged, reversible by evaporation.
  • Cooking an egg: Chemical – proteins denature and new substances form, irreversible.
  • Rusting of iron: Chemical – iron reacts with oxygen to form iron oxide (rust), irreversible.
  • Boiling water: Physical – water changes state from liquid to gas, reversible.
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