[mrfancypants]

What is the difference of a physical and a chemical change?

[RickJ]

Many times, when something changes, it changes both physically and chemically.

So if you're looking for examples of Physical change or Chemical change by themselves, then Physical change would refer to a change of Property: that is changing from liquid to gas, solid to liquid, etc. (There are 4 properties: gas, liquid, solid and plasma).

Chemical change would be like adding a little salt to water.

Does that help?

[RickJ]

Sorry, but my above answer is weak.

A better, more complete answer is here:
http://www.physlink.com/Education/AskExperts/ae244.cfm

"1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change - you can't 'unburn' it

2. A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are 'stuck' together - it's still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren't there when you started."

[rudi_in]

Thank you for posting your question to the Ask Me Help Desk.

When considering a physical change it is important to understand the physical properties associated with the change.

A physical property is basically a characteristic or description of something.

The red sweatshirt.
The mint condition bike.
The birthday cake.
The freezing point of water is 0 ºC.

A physical change is when one or more of these characteristics change without changing the identity of the object or objects involved.

If I wash the sweatshirt and it fades to pink it does not change the fact that it is still a sweatshirt. If it shrinks - it is still a sweatshirt.

If I have an accident and smash up the bike it is still a bike. If I paint it a different color it is still a bike.

If I sit on the cake it is still a cake. If I cut the cake it is still a cake.

A lake that freezes over is still good ol' fashioned H-2-O it is just in a solid form.

Chemical changes involve a reorganization of the atoms that make up something. New substances are formed in chemical reactions.

If I put the sweatshirt on a bonfire it will no longer be a sweatshirt. It will be ashes and some gases.

If the bike rusts it is beginning to change completely from iron to iron (III) oxide, a new compound with new properties.

If I eat the cake, the enzymes in my body will assist other chemicals in my body to break down the cake and create new things. EWWW we won't talk about those :p

H2O can be broken down chemically in a process called electrolysis. By adding an electric current to the water we can change H2O into hydrogen and oxygen gases. Two new substances with new properties.

In short, physical changes involve changing a characteristic and chemical changes involve the breaking and/or forming of chemical bonds to create new things with new properties.