⚖️ Law of Definite Proportions

⚖️ Law of Definite Proportions 

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✅ Definition:

The Law of Definite Proportions states that a given chemical compound always contains the same elements in the exact same proportion by mass, regardless of the sample size or source.

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✅ Who discovered it?

• Joseph Proust, a French chemist
• Proposed the law in 1799
• Also called Proust’s Law

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✅ Key Example:

🔸 Water (H₂O)

• Always made up of Hydrogen and Oxygen
• Mass ratio of Hydrogen : Oxygen = 1 : 8
  → 2g of H + 16g of O = 18g of Water

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🔸 Carbon Dioxide (CO₂)

• Always Carbon : Oxygen = 3 : 8 by mass
  → 12g of C + 32g of O = 44g of CO₂

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✅ Key Points:

ConceptDescription

Fixed composition	The ratio of elements in a compound never changes
Not affected by size	Whether small or large, the proportion stays the same
Helps distinguish	Used to tell apart compounds and mixtures

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✅ Compound vs Mixture

PropertyCompoundMixture

Composition	Fixed ratio ✔	Variable ratio ❌
Example	H₂O, CO₂	Saltwater, air

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📝 Simple Summary Sentence:

"A chemical compound always contains the same elements in the same ratio by mass."