physical properties

[VanNestleroy]

During a phase change does the mass of a substance change?

Part 2

During a chemical change does the amount of matter stay the same?

Thanks.

[dynamicduo]

Yes in both cases though in the second case there may be an apparent change in mass as, for example, some mass may be 'lost' in the form of a gas There could be an 'apparent' gain in mass as combination with a gas could take place. If you take all of the starting materials and all of the products, there will not be a mass change using normal laboratory equipment to measure mass ie ignoring mass energy conversion

[gen2]

Unfortunately, dynamicduo's answer is unclear when he/she states the answer is YES to both.

The last part of that answer is correct - gases have mass and where there is an energy change, there will be an infinitessimal change in mass (E = MC^2).

So, ignoring the energy - mass conversion, the answer to the first question is NO and the answer to the second one is YES.

[dynamicduo]

Yes, I should read the question more closely. Read 'does the amount of matter stay the same' and assumed the question was the same for the physical change.
Agree with gen2
In neither case is there a mass change so PART 1 NO and pPART2 YES

Sorry about the confusion!!

[Peter Pedant]

I agree No and Yes

No-one pick pick pick
has said that in the phase change, the system has to be closed - isnt it usually at const T and P ?

If the system is open then of course you can boil away water, for example

[VanNestleroy]

Thanks to all.. It was a matter of a 50 year old debating a 13 year old....
The part about the closed system was a nice afterthought because the boiling pot of water was an example that we used.