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|Standard Temperature and Pressure (STP)|
Do not confuse STP with the STP Products Company, a maker of oil and fuel additives...unless you are reading one of their MSDS's!
The concept of matter in its standard state (also called "standard conditions") is closely related. "Standard state" does not generally imply a specific temperature, but 25 °C (298 K) is most often used:
|State of Matter||Standard State|
|Gas||1 atm of pressure|
|Elements||The most stable allotrope at STP, with Gf0 = 0|
Many chemistry calculations are for materials that are in their standard state. One very useful rule for gases that does not necessarily require standard state conditions is the Ideal Gas Law (eq 1):
|n||# of moles of material||mole|
|R||The Ideal Gas Constant||0.08206 L.atm.mol-1.K-1|
Using the Ideal Gas Law, one can determine the value of any one of the four variables (P, V, n, T) if we know the value of the other three (R is a constant).
If we wished to calculate this volume at another, non-standard state temperature, such as 100 °C, we would simply substitute 373 K for the temperature (100 °C = 373 K) in the above calculation. The Ideal Gas Law is a very handy equation for estimating gas properties at both standard and non-standard conditions.
Remember: STP is 0 °C, NOT room temperature. Usually the properties at STP versus room temperature vary by less than 10% for gases and even less for liquids or solids. For example, in the calculation in the previous section, the volume would be 858 liters at 20 °C, a difference of 7%. And the density of water is 0.99987 g/ml at 0 °C versus 0.99823 g/ml at 20 °C, a difference of 0.16%.
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