# What is the definition of standard temperature and pressure (STP)?

Oct 5, 2017

Standard Temperature and Pressure is defined by IUPAC as:

• ${0}^{\circ} \text{C}$ and $\text{1.000 bar}$ after 1982
• ${0}^{\circ} \text{C}$ and $\text{1.000 atm}$ before 1982

The numerical difference is that one obtains a molar volume of ideal gas to be:

• $\text{22.414 L/mol}$ at ${0}^{\circ} \text{C}$ and $\text{1.000 atm}$.
• $\text{22.711 L/mol}$ at ${0}^{\circ} \text{C}$ and $\text{1.000 bar}$.

and the universal gas constant is:

• $\text{0.082057 L"cdot"atm/mol"cdot"K}$ at ${0}^{\circ} \text{C}$ and $\text{1 atm}$.
• $\text{0.083145 L"cdot"bar/mol"cdot"K}$ at ${0}^{\circ} \text{C}$ and $\text{1 bar}$.

where

• $\text{1.000 bar}$ $=$ $\text{100000 Pa}$
• $\text{1.000 atm}$ $=$ $\text{101325 Pa}$

As such, you should always specify which pressure your STP uses for your textbook for your course.

Note that ${0}^{\circ} \text{C" = "273.15 K}$. You can always choose to use $\text{273.15 K}$ instead of $\text{273 K}$, and it therefore should not limit the number of significant figures you have in a calculation.