Standard enthalpies on test 1  [ENDORSED]

Moderators: Chem_Mod, Chem_Admin

JennyCKim1J
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

Standard enthalpies on test 1

Postby JennyCKim1J » Sat Jan 20, 2018 7:49 am

For the test, what are the standard states we have to remember? (For example, O2?)

Michelle Dong 1F
Posts: 110
Joined: Fri Sep 29, 2017 7:04 am

Re: Standard enthalpies on test 1

Postby Michelle Dong 1F » Sat Jan 20, 2018 8:33 am

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.

Lily Sperling 1E
Posts: 49
Joined: Tue Oct 10, 2017 7:14 am

Re: Standard enthalpies on test 1

Postby Lily Sperling 1E » Sat Jan 20, 2018 9:40 am

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.

Chem_Mod
Posts: 19137
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 820 times

Re: Standard enthalpies on test 1  [ENDORSED]

Postby Chem_Mod » Sat Jan 20, 2018 12:56 pm

In class I also covered: H2(g); O2(g); N2(g); Cgraphite(g); CO2(g); H2O(l)

AlyssaPeckham1A
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

Re: Standard enthalpies on test 1

Postby AlyssaPeckham1A » Sat Jan 20, 2018 1:00 pm

Also, the diatomic elements all have standard states at zero.

Masih Tazhibi 2I
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

Re: Standard enthalpies on test 1

Postby Masih Tazhibi 2I » Sat Jan 20, 2018 3:44 pm

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.

Michelle Dong 1F
Posts: 110
Joined: Fri Sep 29, 2017 7:04 am

Re: Standard enthalpies on test 1

Postby Michelle Dong 1F » Sun Jan 21, 2018 9:35 am

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?

Karen Ung 2H
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 1 time

Re: Standard enthalpies on test 1

Postby Karen Ung 2H » Sun Jan 21, 2018 1:57 pm

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.


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 2 guests