Observations of chemical reactions are summarized in certain generalizations called the laws of chemical change.  The three laws of chemical change are;

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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12 Comments on "Laws of Chemical Change"

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Gene S.

I don’t understand the laws, can someone explain?

Jack S.

This is nice, it helped me

Rejean B.



tnx a million it help a lot


Tnx a lot it helpd me n my assignment,u guys r doin a great job

Devil Oren

This is so useful and more should make this web site for more learning for generations!


do you have the name of the discoverer of these 3 laws


Thanks! It helped me alot… coz its my assignement… 😀 haha xD


thanks for the help, it helped me a lot… 🙂 its my assignment. ^^