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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: mike on May 22, 2006, 01:15:00 AM

Title: STP (standard temperature and pressure)
Post by: mike 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 :)
Title: Re: STP (standard temperature and pressure)
Post by: AWK on May 22, 2006, 04:51:32 AM
http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure
Title: Re: STP (standard temperature and pressure)
Post by: mike 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.
Title: Re: STP (standard temperature and pressure)
Post by: AWK 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
Title: Re: STP (standard temperature and pressure)
Post by: P 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.
Title: Re: STP (standard temperature and pressure)
Post by: Dan 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.
Title: Re: STP (standard temperature and pressure)
Post by: AWK 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
Title: Re: STP (standard temperature and pressure)
Post by: rjensen 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.

Dr. Roy Jensen
(==========)-----------------------------------------¤
Chemistry, Grant MacEwan College
Edmonton, AB    T5J 4S2
780.633.3915
Title: Re: STP (standard temperature and pressure)
Post by: Borek 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 (http://mailer.uwf.edu/listserv/wa.exe?A1=ind0605&L=chemed-l&D=1#53).

Quote
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.

Quote
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.

Quote
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?

Quote
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.

Quote
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. 
Title: Re: STP (standard temperature and pressure)
Post by: tamim83 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.   ;)
Title: Re: STP (standard temperature and pressure)
Post by: mike on May 22, 2006, 09:44:01 PM
Thanks guys, this is brilliant, exactly the thoughts I wanted to hear. scooby snacks for all!!
Title: Re: STP (standard temperature and pressure)
Post by: billnotgatez 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!

Title: Re: STP (standard temperature and pressure)
Post by: AWK 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 !?
Title: Re: STP (standard temperature and pressure)
Post by: mbeychok 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.
Title: Re: STP (standard temperature and pressure)
Post by: mike on June 01, 2006, 08:08:10 PM
aaah Wikipedia, the new IUPAC? ;)
Title: Re: STP (standard temperature and pressure)
Post by: mbeychok on June 01, 2006, 09:03:01 PM
Mike:

No, the Wikipedia is not the new IUPAC ... and much of the technical and scientific information in Wikipedia has many errors.

But in the case of the Wikipedia article on standard reference conditions, there is a tabulation of the standard reference temperature and pressure conditions used by 15 different organizations including the ISO, NIST, ISA, OPEC and the IUPAC (both the IUPAC's old values of 0 °C and 1 atmosphere as well as the newer values of 0 °C and 1 bar) among others.

That tabulation makes it quite clear that there just isn't any universally accepted set of standard reference conditions and, as I said before, it behooves all of us to carefully state what reference conditions apply to any data or gas measurement we give.
Title: Re: STP (standard temperature and pressure)
Post by: mike on June 01, 2006, 09:16:07 PM
So back to my original question: what do we tell students (high school and undergrad)? Sure we can give them the reaction conditions every time but then they won't even know about STP (maybe this is the way to go to get rid of this "standard" completely). Or do we choose one standard for chemistry (maybe IUPAC) and the specific task (ie ideal gases for example) and make them memorise the STP for those conditions?

I am beginning to think that the term STP is a bit useless, especially as a universal standard. Personally I understand all these in and outs of STP, I am more interested in the thoughts of other chemists (and engineers ;)) on the matter as that is who I am teaching. And before people jump down my thoat, I believe in teaching to the level of the student, so students in high school will be taught a more simplified/global view than University undergraduates, who will be taught a more simple version than post grads etc. So I would like to know peoples thoughts on what to teach late high school early university students.
Title: Re: STP (standard temperature and pressure)
Post by: mbeychok on June 01, 2006, 09:23:01 PM
Mike:

Your last question is a good one ... and I have no answer. What I do know is that just using the acronym "STP" without clearly stating the reference temperature and pressure can and has led to many mistakes that have had serious consequences.
Title: Re: STP (standard temperature and pressure)
Post by: mike on June 01, 2006, 09:29:00 PM
Quote
Your last question is a good one ... and I have no answer. What I do know is that just using the acronym "STP" without clearly stating the reference temperature and pressure can and has led to many mistakes that have had serious consequences.

I agree, I can definitely see how this could happen without stipulating STP. I think our students get frustrated when different departments and different branches of science use STP without qualifying it and then they are marked incorrectly on exams where they have used the wrong STP (Although I would say this has far fewere consequences than in an industrial environment ;) however, these are the scientists of the future and I am often suprised that they don't even seem to question the STP conditions, or realise that there are more than one type.

I think I agree with you, that we should stipulate which STP exactly we are using in the circumstance.

Cheers :)
Title: Re: STP (standard temperature and pressure)
Post by: technologist on June 02, 2006, 08:07:26 AM
Is it Standard Temperature & Pressure in Isolation OR STP conditions used for defining Gas Volume at 1 Atm & 15.5°C, as I read during my school, which derives the Unit Sm3/hr. As far as I remember, 1 Atm & 0°C was used for NTP, which results in Nm3/hr.

However, if U people r discussing std. P & T separately then its fine considering new IUPAC Definitions otherwise, for gas flows I still use Nm3/hr OR Sm3/hr.

Anyway what is the difference in NTP & STP in IUPAC. And any mention about these gas flow units.
Title: Re: STP (standard temperature and pressure)
Post by: mbeychok on June 02, 2006, 11:42:59 AM
technologist:

(1)  Read the article at http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure ... please.

(2)  No matter what you call your reference conditions (Nm3, Sm3, or whatever), please spell out what references temperature and pressure you are using ... otherwise, other people reading your information will use their own definitions and will incorrectly interpret your information.

The world changes and what we once learned and used just isn't universally accepted today.
Title: Re: STP (standard temperature and pressure)
Post by: technologist on June 03, 2006, 12:03:47 AM
OK Milton,
I have already mentioned all condition what were applicable earlier as mentioned in wiki article also, but now still it says that there is no universally accepted Std T & P condition. So questions are-

1. What was the need of defining 2 separate conditions called "STP" (1 Atm & 15.5°C OR 60°F more precisely) and "NTP" (1 Atm & 0°C) earlier?

2. What was the basis for use of them?.

3. Why IUPAC have revised earlier "STP" to "Current so called IUPAC STP"? I mean what forced them to consider the revision in P & T Both?

4. If "Current STP" (I'm using short to save time, if too technicals don't mind. In one of the forums when I used "Kg" as slang for Kgf/Cm2, I found a reaction such that even one of them taught me the total definition of pressure), is 100kPa & 0°C what is the definition of "new NTP"? OR "NTP" still exist or not.

In fact, I am not clear on the need of revising these definitions.
Title: Re: STP (standard temperature and pressure)
Post by: technologist on June 03, 2006, 12:11:24 AM
Dear Milton,

Will there be any change in the values of Gas Constant "R", once basic nos like P & T are revised or it will remian same? I am asking this bcoz I've not read new IUPAC.

Now there are 2 situations in case of R.

1. If it is revised than the result will remain same in totality for any calculation of Vol OR no of moles etc.

2. If it is not revised than result will be erratic due to inconsistent values of same parameters P & T.

This again reflects that change (by IUPAC) was really necessary OR not.
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Title: Re: STP (standard temperature and pressure)
Post by: mbeychok on June 03, 2006, 01:53:55 AM
technologist:

I don't see anything to be gained by wondering why the past standards were different.  However, I'll try to answer some of your questions.

(1) The old Standard T and P of 60 °F and 1 atmosphere was primarily used by the USA, the worldwide petroleum and natural gas industries, and others who still used the set of English or Imperial units.

(2) The old Normal T and P of 0 °C and 1 atmosphere (i.e., 101.325 kPa) was primarily used by those nations adhering to the SI metric units and by those chemists and physicists worldwide who adhered to the old IUPAC definition of standard conditions.

(3) Then in about 1997 (I believe), the IUPAC changed their definition of standard conditions to 0 °C and 100 kPa (i.e., 1 bar).  Why they made the change, I have no knowledge.

(4) Now, in recent years most of the worldwide petroleum and natural gas industries have changed their standard conditions for gas volumes to 60 °F and 14.73 psia (which is slightly more than 1 atmosphere=14.696 psia).  Again, I have no knowledge as to why that change was made.

(5) No, the gas law constant R has not changed nor is there any likelihood that it will change. It is a fundamental constant and it is not dependent on any set of Temperature and Pressure.

(6) No, there is no new Normal T and P. As I've been saying in this thread, there just is no set of standard conditions that are universally accepted any longer.  We must learn to always state what reference conditions of T and P that we are using when we communicate with each other.



Title: Re: STP (standard temperature and pressure)
Post by: technologist on June 03, 2006, 03:30:59 AM
Right Milton,
But its not a question out of curiosity. It was to understand the logic behind the change & how it is going to affect the Chemical Engineering or Science calculations.

I am not clear on your answer No 5 on Gas constant "R".
I agree the Value of fundamental constant will not change but R is having P & V units where it will change from 8.3144 to 8.2058 due to change in Pressure unit from Atm to Bar.

I'm bit confused, how it is going to affect the calculations.
The purpose of discussion is to bring in more clarity for myself.

Answer(6) - Does it mean that now NTP & STP are same?

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Title: Re: STP (standard temperature and pressure)
Post by: Borek on June 03, 2006, 04:19:53 AM
I agree the Value of fundamental constant will not change but R is having P & V units where it will change from 8.3144 to 8.2058 due to change in Pressure unit from Atm to Bar.

R expressed in different units have different numerical values, but this numerical value is only matter of convention - while R per se is an universal constant that doesn't change.

I have read above and I am not sure it will remove confusion :(
Title: Re: STP (standard temperature and pressure)
Post by: mbeychok on June 03, 2006, 07:13:40 PM
R expressed in different units have different numerical values, but this numerical value is only matter of convention - while R per se is an universal constant that doesn't change.

Technologist:

Borek is correct (see above quote).  The fact that IUPAC has changed their definition of standard pressure from 1 atmosphere to 1 bar does not mean that we must use bars as the units of pressure in the ideal gas law equation.  We are free (as we have always been) to use any set of consistent units we want for absolute pressure, absolute temperature, mols, and R ... as long as we explain what we used when communicating with other people.

Borek:

Addressing your concern that confusion may still reign, I don't know how to be more clear than to say "always state the reference conditions of temperature and pressure being used when communicating with others" about information that depends on temperature and pressure.