Law of constant composition

Definition

The law of constant composition states that a given compound always contains the same proportion of elements by mass. This principle is fundamental in understanding chemical formulas and reactions.

5 Must Know Facts For Your Next Test

1. Formulated by Joseph Proust in 1799, the law emphasizes that specific compounds have fixed ratios of their constituent elements.
2. For example, water (H2O) always consists of two hydrogen atoms for every oxygen atom, reflecting consistent mass proportions.
3. This law contrasts with mixtures, where the proportions of components can vary.
4. It supports the concept that chemical compounds are formed through specific interactions between atoms with defined ratios.
5. The law is crucial for chemical stoichiometry and helps predict the outcomes of chemical reactions.

Review Questions

• Who formulated the law of constant composition and in what year?
• How does the law of constant composition apply to a compound like water (H2O)?
• Why is the law of constant composition important for chemical stoichiometry?

Related terms

Chemical Formula: A representation that shows the elements in a compound and their respective proportions.

Stoichiometry: The part of chemistry that deals with calculating the quantities of reactants and products in chemical reactions.

Mixture: A substance made by combining two or more different materials without a fixed composition.