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This topic is offered as a resource for discussions involving STP that may occur on the forum.
It appears that the conventiion we know as STP was changed slightly in 1982.
Here is the current version with history:
Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 atm (101.325 kPa). Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 bar (100 kPa, 105 Pa).
Standard temperature and pressure - WikipediaWikipedia
https://en.wikipedia.org › wiki › Standard_temperature...
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
Note: This web site offers a definition independent of Wikipedia:
https://www.techtarget.com/whatis/defin … essure-STP
Index:
Post #3: https://newmars.com/forums/viewtopic.ph … 60#p229860
GW Johnson reported what he says is a typo in the Wikipedia article
Post #4: https://newmars.com/forums/viewtopic.ph … 61#p229861
kbd512 comments upon the importance of the STP standard and it's relevance to aircraft instruments
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I see a serious typo in the quoted Wikipedia article: 100 Kpa is NOT 105 Pa, it is 100,000 Pa. The 5 should be an exponent. Such an egregious error raises doubt about the accuracy of the whole article.
As to the claim that STP was revised from 1 atm to 1 bar in 1982, I very seriously doubt that! I have seen nothing in any of the science journals, textbooks, or other on-line resources making that claim. The ICAO standard atmosphere that the airlines use has sea level surface pressure at 1 atm, not 1 bar. The ICAO standard day is identical to the old US 1962 standard day to to about 60,000 feet altitude. The standard sea level pressure has been 101.325 KPa = 14.696 psia = 760 mmHg for centuries. Why screw that up? The air pressure is 1.000 bar about 500 feet up. That is NOT sea level!
Check that article again, someone may have since corrected it. I've seen bad stuff posted in Wikipedia before, usually someone corrects it fairly soon.
I also doubt the validity of the change claimed by the linked site for confirmation, because that would goober up the ideal gas law and about 3 centuries worth of thermodynamic tables, not to mention most of the knowledge in most thermodynamics texts and chemistry books. I have no idea who they are, or who the so-called council is that supposedly made the change.
There's more than enough disinformation out there is all of life's other venues. We don't need any disinformation within science.
GW
Last edited by GW Johnson (2025-02-18 10:56:36)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The exact definition of STP is particularly relevant to volatile liquids and gases, such as water vapor and CO2, because it affects mass per unit volume calculation / estimation. The weight of air at 100kPa, and its thermal inertia, vs 101.325kPa, measured over the entire planet, is particularly significant. We would need to ensure that if we were measuring something, relative to some historical baseline value, that we took this redefinition of the term "STP" into account, else the resultant error could be enormous. If any of our instruments or figuring methods were based upon old vs new definitions of STP, then we'd need to be very careful about how we treated old vs new derived data sets, or we could easily arrive at wrong answers. I would think that this is accounted for by any scientists using historical data sets, but rather than believe it was accounted for, I would require evidence indicating that values and figuring methods were updated accordingly.
More than a few otherwise very intelligent scientists have been "caught off guard" by the use of congruent precise definitions and values. One famous example that comes to mind is the mixing of metric and imperial units, which lead to the loss on reentry of a multi-billion dollar Mars probe.
"Thermal inertia" refers to a material's ability to resist changes in temperature, meaning how quickly or slowly it heats up or cools down, essentially acting as a "heat reservoir" by storing and releasing heat over time; it is directly related to a material's mass and specific heat capacity, with materials like stone or concrete having high thermal inertia, while air has low thermal inertia.
Edit:
Come to think of it, aircraft instrument calibrations are now based upon the "International Standard Atmosphere". This is something you really don't want to screw up, or only bad things will happen.
Last edited by kbd512 (2025-02-18 11:15:39)
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For GW Johnson re STP variations
It turns out this is a complex subject. I suspect the punctuation you noted was European punctuation, which uses a period instead of a comma to separate sets of numbers. Or it could be an error. However, in looking at the text below that I just pulled from Wikipedia, I'm inclined to thing the European punctuation is at work.
I note that in this article, a comma is used in a reference to a US institution, and a period is used in a European context.
I also note that there appear to be different institutions involved.
There appears to be an international body for standards for chemistry that is not identical to the US NIST.
In short, this may be a situation in which there is no error and everyone is right, depending upon context.
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In starting this topic, I had assumed that there ** is ** such a thing as "Standard Temperature and Pressure"
With encouragement from GW Johnson and kbd512's postings, I decided to actually ** read ** the Wikipedia article.
It turns out there is NO such thing as a single standard. This topic is available for what I hope will be a thoughtful discussion of the many standards that exist today, let alone all those that have existed and receded into the background.
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