Physics
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Matter

Chemical vs Physical Changes

Molecules Volume



Summary

  • In the right circumstances, the chemical bonds between molecules can be broken, and new bonds formed. (This is known as a chemical reaction.) Example of a chemical change: two H2O molecules react, forming one Oxygen molecule and two Hydrogen molecules.

  • When bond-breaking or bond-forming creates something new, it is known as a chemical change.

  • A physical change is where matter changes its form, but not the molecules its made from. A birthday cake with a slice taken from it Cutting a cake is an example of a physical change. The cake has changed form, but it's still made of the same molecules.

  • Changing state (e.g. freezing, boiling) is a common example of a physical change. Ice melting to form water is an example of a physical change.

  • The number (and type) of atoms stays the same for both chemical and physical changes. For the H2O reaction above, there are 4 Hydrogen atoms and 2 Oxygen atoms both before and after the chemical reaction

  • Therefore, the total mass also stays the same for both chemical and physical changes (this is known as the law of conservation of mass).


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