Standard State

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madisondesilva1c
Posts: 91
Joined: Fri Sep 28, 2018 12:16 am

Standard State

Postby madisondesilva1c » Tue Jan 29, 2019 9:32 pm

In lecture, Professor Lavelle talked about Standard States of pure substances and I was a bit confused on how people knew these so easily. Is this something we should memorize? Or are certain blocks of elements all in the same standard state?

Mindy Kim 4C
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

Re: Standard State

Postby Mindy Kim 4C » Tue Jan 29, 2019 9:35 pm

Generally, O2, F2, Cl2, N2, and all the noble gases are gases in their standard states. All other elements, except Hg and Br (which are liquids) are solids in their standard states.

Jordan Lo 2A
Posts: 85
Joined: Fri Sep 28, 2018 12:25 am

Re: Standard State

Postby Jordan Lo 2A » Tue Jan 29, 2019 10:13 pm

A periodic table that's color coded by state of matter might help if you want to memorize them, but you don't need to

marisaimbroane1J
Posts: 69
Joined: Fri Sep 28, 2018 12:23 am

Re: Standard State

Postby marisaimbroane1J » Tue Jan 29, 2019 11:11 pm

You may want to memorize the diatomic elements (Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine). In a standard state, these elements will always have 2 atoms-- O2, N2, F2, etc. I remember for a test question in 14A, you had to know nitrogen was usually N2 to use the correct molar mass to solve the rest of the question, so they might just be nice to know. If you look up diatomic elements, there are acronyms to remember them if that helps!

Megan_Ervin_1F
Posts: 78
Joined: Fri Sep 28, 2018 12:18 am

Re: Standard State

Postby Megan_Ervin_1F » Wed Jan 30, 2019 1:33 pm

Why is the enthalpy for something in standard state 0?

Megan_Ervin_1F
Posts: 78
Joined: Fri Sep 28, 2018 12:18 am

Re: Standard State

Postby Megan_Ervin_1F » Wed Jan 30, 2019 1:34 pm

Is the reason that N2 has enthalpy of 0 is because N2 goes to N2 so the change in enthalpy is 0? I am confused how you know it is zero

Brian Kwak 1D
Posts: 88
Joined: Fri Sep 28, 2018 12:17 am

Re: Standard State

Postby Brian Kwak 1D » Wed Jan 30, 2019 4:19 pm

Two elements are liquid in their standard state: mercury and bromine.

Eleven elements are gas in their standard state. All of the noble gases (He, Ne, Ar, Kr, Xe, Rn) as well the halogens flourine and chlorine. Hydrogen, oxygen and nitrogen are the others.

All other elements are solid in their standard state.

Therefore for these elements if they were in their standard state then the Standard Enthalpy State for these molecules would be zero because the elements are in their most stable state.
Standard Enthalpy Formations also have to be in the conditions of 1 atm and 25 degrees celcius which would be the standard conditions.
Hope this helps a bit.


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