Chapter : 3. Atoms & Molecules
Law of Constant Proportions
(B) Law of constant proportions
This law was discovered by the french chemists, A. Lavoisier and Joseph Proust. A pure chemical compound always contains same elements combined together in same proportion by mass
Ex. Pure water obtained from different sources such as river, well, spring, sea, etc., always contains hydrogen and oxygen combined together in the ratio 1 : 8 by mass.
Limiting reagent : In a reaction having more than one reactant we must identify the limiting reagent “Reagent which is finished early is known as limiting reagent ”.
Example : - In Haber’s process to manufacture NH3,
N2 + 3H2 → 2NH3
If we take 2 moles of N2 (56 grams) along with 3 moles of H2 (6 grams) we can see that only 1 moles of N2 (28 grams) is sufficient to react with 3 moles of H2. It means 1 mole N2 (28 grams) is in excess & H2will be finished when reaction will be completed or H2is limiting reagent.
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