Why does the Dry Air Gas Constant vary?

In summary, the dry air gas constant varies slightly between different sources, with values ranging from 286.9 to 287.22. This is due to differences in measurement methods and improvements over time. However, for practical purposes, a value of 287.05 can be used, as it is accurate to within 3 significant figures. The universal gas constant is 8314.32 in the 1976 Standard Atmosphere, and the molecular weight of dry air is 28.964. While the exact value may not be attainable, this should not hinder calculations.
  • #1
Robert James Liguori
5
0
I'm confused on why the dry air gas constant varies:
Can someone please explain why it differs and how it is constructed. Thanks, Robert

Reference:
[link to personal website removed]
 
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  • #2
to within 3 significant figures these are all the same !
It would be worth checking how each source obtained the value, especially the date when the values were measured.
Methods vary and improve over the years
 
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  • #3
I am not a physicist... so you are implying that the differences in the values is insignificant? To me, it should be exact... or a means should be in place to get the exact value at each given location of sampling... if this was indeed possible, which it may not be. Please advise.
 
  • #4
universal gas constant = 8314.32 (in 1976 Standard Atmosphere)
molecular weight of dry air = 28.964

8.3143 / 28.964 = 0.28705634580859 (e.g., 287.056)
 
  • #5
I figured it out... thanks for your help.

[link to personal website removed]
 
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  • #6
Can you measure the length of your kitchen table exactly? Why not? Are you going to let that keep you from buying a tablecloth?

Even if the value of the gas constant is not exact, does that bring your calculations to a screeching halt (until you find the exact value, which doesn't exist)? Isn't 3 significant figures accurate enough for you?
 
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  • #7
On these words of wisdom, the OP's question has been answered. Thread closed.
 

Related to Why does the Dry Air Gas Constant vary?

1. Why does the Dry Air Gas Constant vary among different gases?

The Dry Air Gas Constant, also known as the specific gas constant, varies because each gas has its own unique molecular structure and properties. This leads to differences in the amount of energy required to raise the temperature of each gas by 1 degree Celsius. Therefore, each gas has its own specific gas constant.

2. How does temperature affect the Dry Air Gas Constant?

The Dry Air Gas Constant is directly proportional to temperature. This means that as the temperature increases, the value of the constant also increases. This is because higher temperatures lead to an increase in the average kinetic energy of gas molecules, resulting in more collisions and a higher pressure.

3. What is the significance of the Dry Air Gas Constant in gas laws?

The Dry Air Gas Constant is a crucial factor in gas laws, such as the Ideal Gas Law, which relates the pressure, volume, temperature, and amount of a gas. It helps to determine the behavior of gases and their properties under different conditions. It is also used in calculations to convert between different units of measurement.

4. How does the Dry Air Gas Constant vary with altitude?

As altitude increases, the atmospheric pressure decreases, leading to a decrease in the density of gases. This results in a decrease in the Dry Air Gas Constant. This is because there are fewer gas molecules in a given volume, resulting in fewer collisions and a lower pressure.

5. Why is the value of the Dry Air Gas Constant different for different units of measurement?

The value of the Dry Air Gas Constant depends on the unit of measurement used. For example, in SI units, the value is 8.314 J/mol·K, while in imperial units, it is 1.985 cal/mol·K. This is because different units of measurement use different reference points and scales, resulting in different numerical values for the constant.

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