Hey it’s professor Dave, let’s define standard conditions.
In order to do science, we must do experiments, and when we do these experiments, the data
we collect will allow us to do calculations.
Any relevant calculations may depend on certain environmental factors like temperature and
pressure, and sometimes humidity, and these parameters can have a range of values.
We can do experiments at very low pressures, or even zero pressure if in a vacuum, or we
can do experiments in highly pressurized environments.
We can do experiments at very low temperatures, near absolute zero, or we can do experiments
at very high temperatures, using a flame or even under explosive conditions.
But many or most of our experiments are done in open atmosphere under what we can refer
to as standard conditions.
These are standard sets of conditions for experimental measurements set by the International
Union of Pure and Applied Chemistry, or IUPAC, that allow easy comparisons to be made between
data sets all over the world.
The first set we will discuss is called standard temperature and pressure, abbreviated as STP.
This refers to a temperature of zero Celsius, or 273.15 kelvin, and a pressure of 100 kilopascals,
or precisely one bar.
Another set, called standard ambient temperature and pressure, abbreviated as SATP, sets the
temperature at 25 degrees Celsius, or 298.15 kelvin, which is roughly room temperature,
and pressure once again is set at 100 kilopascals or one bar.
So the difference between these two sets is the difference between the freezing point
of water and room temperature.
Sometimes when people refer to standard conditions, they mean standard state conditions.
This includes a temperature of 25 celsius, and a pressure equal to atmospheric pressure
at sea level, which by definition is one atmosphere.
This can also be expressed as 760 millimeters mercury, or 101.325 kilopascals, which is
extremely close to the pressure previously discussed for STP.
Standard state conditions can also refer to concentration, more specifically to solution
concentrations of precisely one molar for any solute.
The point of these sets is that so much science is done at the ambient temperature and pressure
of a normal laboratory, and noting this allows us to make simplifications to our equations
that allow for easier calculations, and also allows for the compilation of standardized
tables of data that we can plug into our equations.
However, the idea of a standard laboratory temperature and pressure is inevitably culture
bound, since different regions of the world differ greatly in climate, altitude, and access
to heating or cooling technology, so this must be kept in mind when communicating science
amongst one another.
In the end, when looking at tabulated constants and reported data, be sure to note the conditions
listed to put them in the proper context, and be sure to make note of the conditions
in your own laboratory when doing experiments.