Measuring activities with a Knudsen cell

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  • #1
lalbatros
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2
Hello

I would like to find some texts or web sites explaining how and why activities can be measured with a Knudsen cell. What is measured and how the Gibbs energy is deuced from the measurements.

I would also like to find out the range of application of this method, like for temperatures.

Thanks,

Michel
 
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  • #2
I've actually researched a bit on electric cells, perhaps you can find something here (try to browse under electrolysis etc)

http://groups.msn.com/GeneralchemistryHomework/methodsofanalysis.msnw [Broken]
 
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1. What is a Knudsen cell and how does it measure activities?

A Knudsen cell is a type of instrument used in high vacuum environments to measure the partial pressure of gas species. It works by heating a sample of the gas to a high temperature, causing it to evaporate and form a molecular beam. The Knudsen cell then measures the number of gas molecules in the beam, which is directly related to the activity of the gas species.

2. How accurate are measurements taken with a Knudsen cell?

The accuracy of measurements taken with a Knudsen cell can vary depending on factors such as the type of gas being measured and the temperature of the cell. However, in general, Knudsen cells are highly accurate and can provide precise measurements with an error of less than 1%.

3. What types of gases can be measured with a Knudsen cell?

Knudsen cells are commonly used to measure the activities of noble gases such as helium, neon, and argon. However, they can also be used to measure other gases, including hydrogen, nitrogen, and oxygen. The type of gas that can be measured depends on the temperature of the Knudsen cell and the type of material used to construct it.

4. How does the temperature of the Knudsen cell affect the measurements?

The temperature of the Knudsen cell is a critical factor in determining the accuracy of the measurements. Higher temperatures can cause more gas molecules to evaporate, resulting in a higher activity measurement. However, at extremely high temperatures, the gas molecules may break down, leading to inaccurate readings. Therefore, it is essential to carefully control the temperature of the Knudsen cell during measurements.

5. Are there any limitations to using a Knudsen cell for activity measurements?

While Knudsen cells are highly accurate and widely used in scientific research, they do have some limitations. For example, they can only be used in high vacuum environments, and the temperature range in which they can operate is limited. Additionally, Knudsen cells are not suitable for measuring the activities of gases with very low vapor pressures, such as water vapor.

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