Diffrence between Chemical and 'chemical substance'

[Van Khanh]

Please tell me the difference btw "advise" and "recommend" in:

a. It's a chemical.
b. It's a chemical substance.

Are they the same meaning?

Thanks

[Pamela]

A chemical substance is any material with a definite chemical composition, no matter where it comes from.For example, a sample of water has the same properties and the same ratio of hydrogen and oxygen whether the sample is isolated from a river or made in a laboratory. A pure substance cannot be separated into other substances by any mechanical process

chemical-a distinct compound or substance, especially one which has been artificially prepared or purified.