# What is Standard Temperature and Pressure (STP)?

Jan 20, 2016

Some textbooks define it differently than others, but the newest IUPAC standard temperature and pressure are:

${T}_{\text{STP" = 0^@ "C" = "273.15 K}}$
${P}_{\text{STP" = "1 bar}}$

Some older (and potentially fairly recent) textbooks might say:

${T}_{\text{STP" = 0^@ "C" = "273.15 K}}$
${P}_{\text{STP" = "1 atm}}$

The difference between the two pressures are subtle but significant:

$\text{1 bar} = 1.00000 \times {10}^{5}$ $\text{Pa}$
$\text{1 atm} = 1.01325 \times {10}^{5}$ $\text{Pa}$

This leads to a difference of about $\text{0.3 L}$ for the molar volume $\left(\overline{V} = \frac{V}{n}\right)$ of an ideal gas at STP when you calculate it using the Ideal Gas Law: ~"22.7 L" for the former, and ~"22.4 L" for the latter.

Ever had your university lab notebook "torn apart" by a lab TA for "not enough information"? Yeah, it's primarily because science tends to rely on consistency and reproducibility to prove that something is credible.

If someone can't read your lab notebook and then reproduce your lab experiment without your input and correction, you haven't provided enough information to replicate that experiment precisely.

IUPAC has defined such standards so that people have consistent atmospheric conditions to use for comparisons of data from different experimental trials for the same type of experiment. That improves the accuracy to which an experiment can be reproduced.

SIDENOTE: This is not be confused with the temperature and pressure at which $\Delta {H}_{f}^{\circ}$, $\Delta {S}^{\circ}$, and $\Delta {G}^{\circ}$ are defined, which you should have in your textbook appendix; those are derived and defined (usually) for ${25}^{\circ} \text{C}$, not ${0}^{\circ} \text{C}$.

May 25, 2016

STP is Standard Temperature and Pressure

#### Explanation:

STP is Standard Temperature and Pressure

Standard Temperature is

${0}^{o} C$ in Celsius or $273 K$ in Kelvin

Standard Pressure is

$1$ Atmosphere (atm)
$760$ Torrcellis (torr)
$760$ Millimeters of Mercury (mmHg)
$101.325$ KiloPascals (kPa)