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Standard enthalpies on test 1

Posted: Sat Jan 20, 2018 7:49 am
by JennyCKim1J
For the test, what are the standard states we have to remember? (For example, O2?)

Re: Standard enthalpies on test 1

Posted: Sat Jan 20, 2018 8:33 am
by Michelle Dong 1F
We should probably know that everything in the halogens group's standard states are in gases, except for Br2, whose standard state is in liquid form, and I2, whose standard state is in solid form.

Re: Standard enthalpies on test 1

Posted: Sat Jan 20, 2018 9:40 am
by Lily Sperling 1E
Yes, I would assume the halogens and the transition metals. Dr. Lavelle said if it is some element we wouldn't know, he would give us the standard state.

Re: Standard enthalpies on test 1  [ENDORSED]

Posted: Sat Jan 20, 2018 12:56 pm
by Chem_Mod
In class I also covered: H2(g); O2(g); N2(g); Cgraphite(g); CO2(g); H2O(l)

Re: Standard enthalpies on test 1

Posted: Sat Jan 20, 2018 1:00 pm
by AlyssaPeckham1A
Also, the diatomic elements all have standard states at zero.

Re: Standard enthalpies on test 1

Posted: Sat Jan 20, 2018 3:44 pm
by Masih Tazhibi 2I
It's important to also know that the reason diatomic molecules have standard enthalpies of formation at zero is not because they are diatomic in and of itself, but it is a consequence of the fact that diatomic elements are pure substances. For example, molecules like C(s) or K(s) or O2 etc., are all composed of one element. Because standard enthalpies of formation are derived from the reaction of constituent elements making the substance at hand, it makes sense to see how a carbon atom forming itself, or more accurately remaining as a carbon atom, would not have any enthalpy change.

Cheers.

Re: Standard enthalpies on test 1

Posted: Sun Jan 21, 2018 9:35 am
by Michelle Dong 1F
When a molecule is diatomic, does that mean they have the same atoms (eg: H2 (g)) or do they also have different atoms? If they have different atoms, is the standard enthalpy change still 0?

Re: Standard enthalpies on test 1

Posted: Sun Jan 21, 2018 1:57 pm
by Karen Ung 2H
Diatomic molecules are made of two elements. The seven diatomic elements from the periodic table are nitrogen, oxygen, bromine, iodine, chlorine, hydrogen, and fluorine. Because they are the same elements, they have a standard enthalpy change of 0.