Asked in Chemistry
What is the difference between a chemical and a physical change?
March 19, 2018 12:43PM
Physical changes are reversible (reversal is often quite easy).*
Chemical changes are not reversible (reversal is often extremely difficult). *
The chemical composition of materials is different after a chemical change but the same after a physical change.
Bonds have changed; the substances present before the change, are different from those present after the change:
A substance reacts to form a new chemical entity
same atoms are used, but different molecules have been created.
The electrolysis of water: the products are two different substances;
Combustion of hydrogen in oxygen; forms water and generates heat;
The body's combustion of glucose produces carbon dioxide and water;
Bread made into toast (partially oxidized bread) is not reversible;
Wood burned in a fireplace is not reversible;
Burning of the World Trade Center.
State, size, shape, or color of a substance is changed basic character-unchanged; Change of physical properties, leaving basic character-unchanged.
Melting of ice: change of state;
Bearing gold into a ring;
Collapse of the World Trade Center
* Physical changes aren't always easy to reverse, and chemical changes aren't necessarily impossible to reverse.