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Topic: STP (standard temperature and pressure)  (Read 34567 times)

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Offline mike

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STP (standard temperature and pressure)
« on: May 22, 2006, 01:15:00 AM »
I have just been reading some old posts that talk about STP and the advice that is always given is that STP is 1atm and 0C. I was looking through the IUPAC definitions and read that STP is 0C and 100000Pa. Now I think some places still use 1atm (I think ISO), my question I guess is how should we be answering this question for students so as to make it unambiguos, or to put it another way can people put forward their thoughts on which STP is used when and where. (BTW is this has already been discussed in detail here then let me know, I did search but only found bits and pieces). Cheers :)
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Offline AWK

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Offline mike

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Re: STP (standard temperature and pressure)
« Reply #2 on: May 22, 2006, 08:11:17 AM »
Yes, thankyou AWK but I have already read this entry in wikipedia and ahve read the IUPAC definitions etc, but I was more after what the chemist on this forum thought.
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Offline AWK

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Re: STP (standard temperature and pressure)
« Reply #3 on: May 22, 2006, 09:05:49 AM »
Before IUPAC definition all chemist and physicist used pressure at the surface of the sea (760 torr, 1 atm - physical atmosphere, or 101313 Pa), now we should use 105 Pa
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Offline P

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Re: STP (standard temperature and pressure)
« Reply #4 on: May 22, 2006, 09:39:25 AM »
I've just read the definitions. I didn't even realise it was 0C  -  I always took it as room temp (20C) and 1atm.
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Offline Dan

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Re: STP (standard temperature and pressure)
« Reply #5 on: May 22, 2006, 09:51:49 AM »
Well, Peter Atkins told me that "standard temperature" is meaningless. I suppose, because it varies so much, there is no standard temperature. All the questions I get at uni ALWAYS specify the temperature (or ask me to work out what it is).

In school, standard temperature was 298K.

Unless otherwise stated, standard pressure is always 1 bar = 1000 kPa as far as the UK is concerned.
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Offline AWK

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Re: STP (standard temperature and pressure)
« Reply #6 on: May 22, 2006, 10:22:59 AM »
Well, Peter Atkins told me that "standard temperature" is meaningless. I suppose, because it varies so much, there is no standard temperature. All the questions I get at uni ALWAYS specify the temperature (or ask me to work out what it is).

In school, standard temperature was 298K.

Unless otherwise stated, standard pressure is always 1 bar = 1000 kPa as far as the UK is concerned.
Peter Atkins is right. In termodynamics 25 , 20 C or 22 C as standard temperature  is often used, especially the first one.
But the most meaningless is room temperature (RT) often used in synthetic works.

And correction: 1 bar =100 kPa, not 1000 kPa
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Offline rjensen

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Re: STP (standard temperature and pressure)
« Reply #7 on: May 22, 2006, 12:54:38 PM »
ISO defines the 'standard pressure' as 100 kPa, changed from 101.325 kPa in 1982.
IUPAC, IUPAP, government, and industry are all part of the decision-making bodies established by ISO, and have adopted these values as well. Individual companies cannot be forced to comply.

Two standards exist:
STP - standard temperature and pressure: 273.15 K (0 °C) and 100 kPa
SATP - standard ambient temperature and pressure: 298.15 K (25 °C) and 100 kPa

Note that there is no 'standard' temperature in thermodynamics. I.e., the temperature must be reported when specifying a deltaH° value.

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Offline Borek

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Re: STP (standard temperature and pressure)
« Reply #8 on: May 22, 2006, 05:13:31 PM »
mike: I have forwarded your question to CHEMED-L, as I know from experience that you may get interesting comments there. I was about to post summary of what was told there, but I see Roy Jensen have already posted his comment - so I will not repost it now.

Note that whole discussion from CHEMED-L (together with info on who posted what) is visible here.

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http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

has a nice discussion of this. So, my two cents:

1) Use your textbook's definition.
2) Explain that there exist numerous definitions of STP. (Science is a human enterprise, with history and differing points of view.)
3) Have students do a calculation that uses two different definitions and see if it makes any significant difference in their answer.
4) Avoid it. Be specific in class in terms of actual pressure and temperature.

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Those are all really good suggestions.  I guess the problem that remains is that students might face STP problems on standardized test, without any indication of which STP the test writers are using.

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The HS text I'm using (not exactly an authority, but...) mentions two standards, STP (0C and 101.325 kPa) and SATP ("standard ambient temp and pressure") which is 25C and 100 kPa. Could it be that your correspondent is mixing the two up?

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STP ised to be 273.15 K and 1.000 atm.  It is a ggod idea to make the small shift to 0.1000 MPa = 100000 Pa for standard pressure, but it is confusing to have two different standards with the same notation, STP.  We also have to consider the standards of temperature and pressure for thermodynamics, 298.15 K and 0.100 MPa.  My advice is to shift all the way, declare to your students that you are using 298.15 K and 0.1000 MPa as new standard temperature and pressure, and call it nSTP.

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Roy and Reed have clarified current usage of "STP" vs. "STAP".

A question: Why do we need STP?

The only place I've seen this being employed is on chemistry tests of various kinds, with respect to gas laws. I suggest that it would make a great deal more sense to teach kids that Standard Conditions for MOST usage is 25 C and the newly defined standard (atmospheric) pressure 100 kPa (very nearly the Canadian 750 torr/atm). Here, molar volume of an ideal gas is 24.46 L, which is about as easy to remember as 22.414L by all but the case-hardened.

While Roy Jensen is generally correct when he notes that:
Quote
there is no 'standard' temperature in thermodynamics. I.e., the temperature must be reported when specifying a deltaH° value.

it is also true that the vast majority of data reported are at "standard conditions" of 1 atm (whichever way defined) and 25 C; only in some very old tabulations are 0 C values reported.

Isn't it time for this anachronistic representaton to be retired?

Quote
Correction:  I guess I was(n't) thinking - of the correct pressure when I cited 24.6 L for molar volume at "standard conditions"; it should have read 24.8 L. In fact, to emphasize that it is an approximate relationship for real gases, why not just call it "twenty five at twenty five"?

I agree that the temperature for many thermo properties must be specified, but tabulations such as enthalpies or free energies of formation or combustion are, for the most part, for 25 C, not 0 C or some other temperature. 
« Last Edit: May 24, 2006, 04:35:19 AM by Borek »
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Offline tamim83

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Re: STP (standard temperature and pressure)
« Reply #9 on: May 22, 2006, 09:33:05 PM »
Wow, I had no idea that STP was ever "redefined" in any way!  It is very strange since here in the US we learned that STP was 1atm (101.325kPa) and 0oC.  I don't even remember mention of this in any textbook I used (I need to check my Atkins Pchem book again though)  Hmm, interesting, I will need to look out for that when I teach in the fall.   ;)

Offline mike

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Re: STP (standard temperature and pressure)
« Reply #10 on: May 22, 2006, 09:44:01 PM »
Thanks guys, this is brilliant, exactly the thoughts I wanted to hear. scooby snacks for all!!
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Offline billnotgatez

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Re: STP (standard temperature and pressure)
« Reply #11 on: May 24, 2006, 04:26:55 AM »
Just to throw in an odd one here. I seem to recollect that when doing calibration of aircraft turbine engines performance we used 15C temperature and sea level pressure. I think it then got extrapolated to a centigrade versus feet chart. Go figure!


Offline AWK

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Re: STP (standard temperature and pressure)
« Reply #12 on: May 25, 2006, 02:53:27 AM »
In my native language an other univocal term exist for STP - normal conditions (760 torr ,0 C), but we are in IUPAC !?
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Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #13 on: June 01, 2006, 07:06:37 PM »
Anyone who carefully reads the Wikipedia article referenced in this thread by AWK on May 22nd, namely http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure will realize that there really is no universally used standard temperature and pressure. For that reason it behooves us to always ... repeat always ... specify the temperature and pressure whenever we want to reference the conditions applicable to a data measurement or a gas quantity or whatever.
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Offline mike

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Re: STP (standard temperature and pressure)
« Reply #14 on: June 01, 2006, 08:08:10 PM »
aaah Wikipedia, the new IUPAC? ;)
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