Atmospheric pressure 1Atm or 100 kPa?

• flatmaster
In summary, atmospheric pressure has two conventions for measurement: 1 Atm = 101,325 Pa and 1 Atm = 100 kPa. This has caused confusion in determining the standard conditions for temperature and pressure (STP). While IUPAC uses 100 kPa, NIST and most ISO standards use 101.3 kPa. However, the average atmospheric pressure is still considered to be 1 Atm. When choosing units, it is recommended to stick to SI units, but using Atm can be helpful in comparing to other pressures, such as 4.5 Atm at the bottom of a local lake.

flatmaster

Ignoring normal variations, I've always been told that atmospheric pressure is...

1 Atm = 101,325 Pa

However, Wikipedia says atmospheric pressure was re-defined in 1999 to be exactly 100 kPa. This would mean that atmospheric pressure is now 0.98692 Atm.

http://en.wikipedia.org/wiki/Atmospheric_pressure

I'm writing a lab activity for high school students. From what I've read, it seems that both conventions are used. Which convention should be used?

it depends who you work for !
IUPAC use 100Kpa but NIST use 101.3Kpa, as do most ISO standards.

None of these change the fact that the average air pressure is 101.3kpa

ok. average atmospheric pressure = 1 Atm and that's that. Good enough for now. I'll let them be confused later.

Using Atm allows me to compare 1Atm to 4.5 Atm at the bottom of a local lake and 3,000,000 Atm at the core.

Could be a good point, but... where do you get 4.5 atm from?

Borek said:
Could be a good point, but... where do you get 4.5 atm from?

It's a local lake. I calculated it myself from the depth.

So I guess lake is 45 m deep?

1. What is atmospheric pressure?

Atmospheric pressure is the force per unit area exerted by the weight of the Earth's atmosphere on the surface of the Earth. It is commonly measured in units of atmospheres (atm) or kilopascals (kPa).

2. What is the standard atmospheric pressure?

The standard atmospheric pressure at sea level is 1 atm or 101.325 kPa. This is also known as the average atmospheric pressure at sea level.

3. How does atmospheric pressure change with altitude?

As altitude increases, the amount of air above decreases, resulting in a decrease in atmospheric pressure. This is because there is less weight of air pushing down on the surface at higher altitudes.

4. How is atmospheric pressure measured?

Atmospheric pressure is typically measured using a barometer, which measures the weight of a column of mercury in a tube. Other methods include using aneroid barometers, which use a vacuum chamber and a spring, and electronic sensors.

5. How does atmospheric pressure affect the weather?

Changes in atmospheric pressure can indicate changes in weather patterns. High pressure systems are associated with clear skies and fair weather, while low pressure systems are associated with cloudy and potentially stormy weather.