Chemical and Physical Changes - Lab Questions

[Jessica]

I need help with this question:

The following changes often indicate that a chemical change has occurred. But they can also indicate the occurrence of a physical change. Explain how each change might result from a physical change, not a chemical change.

1. Change of color: Painting it
2. Loss of mass: If it is clay, take a chunk from it
3. The substance seems to "disappear":

I am stuck with #3 and are the other 2 O.K. answers? Are there better answers? What other ones could they be?

[Tomisimo]

I assume a chemical change would be if matter changes state or reacts with something else, and a physical change is when some other external means affects the matter. If that is an accurate description, then I'd say you have numbers 1 and 2 right, and for three, if we were talking about water, then a chemical change that makes it disappear could be evaporation or boiling it away, since it changes state, but then if the water leaked out of the recipient, it would be a physical change making it seem to disappear.

That is just a guess, I'm not too sure on that.

[Jessica]

So water leaking out of something would be a physical change of something disappearing?
anyone have other ideas?

[Tomisimo]

Originally Posted by jchen

So water leaking out of something would be a physical change of something disappearing?
anyone have other ideas?

I think so, but I'm not sure. Do you have a definition of "chemical change" and "physical change" in your textbook? If so, post it here.

[Jessica]

Physical Change and Properties:

Matter has physical properties like color, odor, shape, texture, taste, and hardness.
Two other important physical properties are melting point and boiling point.
Physical properties of matter can be observed and measured without permanently changing the identity of the matter.

Chemical Change and Properties:

Matter has chemical properties also.
Chemical properties describe a substance's ability to change into another new substance as a result of chemical change.
A chemical change is a process in which a substance is permanently altered.

[Tomisimo]

According to those definitions, water boiling away or evaporating away would be a physical change, not a chemical change.

[Jessica]

ok thanks!

[Tomisimo]

You're welcome.