Standard enthalpies on test 1 [ENDORSED]

[JennyCKim1J]

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

[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.

[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.

[Chem_Mod]

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

[AlyssaPeckham1A]

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

[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.

[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?

[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.