Question

Which best describes why a chemical change is different than a physical change

Answer 1

The difference between physical change and chemical change is that while physical change basically involves a change in state of matter and energy, chemical change occurs at the molecular level. Chemical change brings about the creation of a new substance different from the original and is not reversible while in physical change, the substance remains the same though there may be a change in state of matter. Melting of ice is a physical change while resting of iron is a chemical change.

Answer 2

Physical changes are reversible (reversal is often quite easy).*
Chemical changes are not reversible (reversal is often extremely difficult).*

Related Information:

Chemical 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.

Examples:

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.

Physical Change:

State, size, shape, or color of a substance is changed basic character-unchanged; Change of physical properties, leaving basic character-unchanged.

Examples:


Melting of ice: change of state;

Bearing gold into a ring;

Grinding;

Cutting;

Folding;

Collapse of the World Trade Center


* Physical changes aren't always easy to reverse, and chemical changes aren't necessarily impossible to reverse.