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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: antoinetta on September 10, 2006, 08:57:06 PM

Title: Chemical vs Physical Change
Post by: antoinetta on September 10, 2006, 08:57:06 PM: Hello, I seem to have trouble differentiating between chemical vs physical change for the following: Would somebody mind checking my responses?

i) toaster filament becomes red hot - physical
ii) grease spot is dissolved with cleaning fluid - chemical
iii) heated oil turns brown - chemical
iv) alkaline flashlight battery discharges - chemical
Title: Re: Chemical vs Physical Change
Post by: P-man on September 10, 2006, 09:00:25 PM: It looks correct :).
Title: Re: Chemical vs Physical Change
Post by: Korokian on September 10, 2006, 09:12:20 PM: looks good to me....
Title: Re: Chemical vs Physical Change
Post by: constant thinker on September 10, 2006, 09:34:56 PM: That's a hard concept to kind of explain. All one can really say about it is, a chemical change involves the change of a molecule and you can apply a chemical formula. A physical change is something that doesn't change the molecule.

Also chemical changes happen at the micro level while physical changes usually happen at the macro level.

O, and your things are right.
Title: Re: Chemical vs Physical Change
Post by: Donaldson Tan on September 10, 2006, 09:42:31 PM: Macroscopic description of a chemical change is that it involves a change in composition in a close system.
Title: Re: Chemical vs Physical Change
Post by: Yggdrasil on September 10, 2006, 09:51:51 PM: Quote from: antoinetta on September 10, 2006, 08:57:06 PM
ii) grease spot is dissolved with cleaning fluid - chemical

I think this is just a physical change. The grease does not react with cleaning fluid; it just becomes sequestered and disolved in detergent micelles.
Title: Re: Chemical vs Physical Change
Post by: Borek on September 11, 2006, 02:36:56 AM: Quote from: Yggdrasil on September 10, 2006, 09:51:51 PM
I think this is just a physical change. The grease does not react with cleaning fluid; it just becomes sequestered and disolved in detergent micelles.

I second that.
Title: Re: Chemical vs Physical Change
Post by: P on September 11, 2006, 09:08:02 AM: I too would have said that this is a physical change as no 'chemistry' takes place.
Title: Re: Chemical vs Physical Change
Post by: jennielynn_1980 on September 11, 2006, 12:29:12 PM: What about sugar dissolving in water. Is that chemical or physical? Does the lump of sugar break up into tiny sugar molecules or do the actual carbon and hydrogens bond with the water molecules?
Title: Re: Chemical vs Physical Change
Post by: Yggdrasil on September 11, 2006, 01:00:19 PM: The lump of sugar disolves into single sugar molecules and no chemical bonds (i.e. covalent bonds) are broken. Only intermolecular bonds (bonds between molecules like hydrogen bonds, dipole-dipole interactions, and van der Waals forces) are broken.
Title: Re: Chemical vs Physical Change
Post by: Donaldson Tan on September 11, 2006, 03:15:49 PM: In dissolving sugar, the molecular integrity of sugar is maintained in the process.
Title: Re: Chemical vs Physical Change
Post by: constant thinker on September 11, 2006, 03:37:17 PM: Now that Yggdrasil and Borek mention it...

Number 2 is a physical change. I didn't put much thought into, but Yggdrasil's explanation makes it out to be a physical change. Which I now agree with after thinking about it.

Geodome's comment seals the deal though. I now have to agree it's a physical change.
Title: Re: Chemical vs Physical Change
Post by: antoinetta on September 11, 2006, 07:28:44 PM: Hey, thanks for everyone's reply. It certainly clarify things.