Observations of chemical reactions are summarized in certain generalizations called the laws of chemical change. The three laws of chemical change are;
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1) Law of Conservation of Mass
2) Law of Constant Composition
3) Law of Multiple Proportions
Law of Conservation of Mass
- States that during a chemical reaction, matter is neither created or destroyed
Mass of reactants = mass of products
Law of Constant Composition
- The percentage composition by mass in particular compounds never varies
- In other words, in the formation of a compound, the mass of 1 element needed to combine with a given mass of another is always the same
- E.g. 39.37% Na : 60.73% Cl for compound NaCl
Law of Multiple Proportions
- Atoms of 2 elements can combine in more than 1 way
e.g. elements H & O can form water (H2O) and hydrogen peroxide (H2O2)
—both have different physical and chemical properties despite containing the same atoms i.e. H2O2 bleaches most dyes while H2O does not
- When the proportions (by mass) in which 2 elements combine to form 2 different compounds are divided by each other, the result is a fraction composed of small whole numbers
Or in other words…..
- When 2 elements, A and B, form more than one compound, the mass of element A divided by the mass of element B in one compound, compared with mass of A divided by the mass of B in the second compound gives a ratio of small whole numbers
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