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Topic: STP (standard temperature and pressure)  (Read 34581 times)

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Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #15 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.
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Offline mike

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Re: STP (standard temperature and pressure)
« Reply #16 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.
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Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #17 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.
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Offline mike

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Re: STP (standard temperature and pressure)
« Reply #18 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 :)
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Offline technologist

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Re: STP (standard temperature and pressure)
« Reply #19 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.

Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #20 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.
« Last Edit: June 02, 2006, 06:49:19 PM by mbeychok »
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Offline technologist

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Re: STP (standard temperature and pressure)
« Reply #21 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.

Offline technologist

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Re: STP (standard temperature and pressure)
« Reply #22 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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Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #23 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.



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Offline technologist

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Re: STP (standard temperature and pressure)
« Reply #24 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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Offline Borek

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Re: STP (standard temperature and pressure)
« Reply #25 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 :(
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Offline mbeychok

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Re: STP (standard temperature and pressure)
« Reply #26 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.
Milton Beychok
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