What determines the pressure inside this experimental setup?

In summary, the pressure inside the experimental setup is determined by several key factors, including the temperature of the gas, the volume of the container, and the number of gas molecules present. Additionally, interactions between the gas particles and the walls of the container, as well as external forces acting on the system, can influence the pressure readings. Understanding these variables is essential for accurately interpreting the results of the experiment.
  • #1
Dario56
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I have two gas tanks of nitrogen and oxygen. Mixture of gases is created and used in the system of interest.

Let's say I want to create an atmospheric conditions in my system, mass ratio of oxygen to nitrogen is 0.3 and total pressure of 1 bar (oxygen partial pressure 0.21 bar). Therefore, mass flow ratio of the gases needs to be 0.3 to create a gas mixture of atmospheric composition. Gas tanks are equipped with volumetric flowmeters. This isn't a problem as mass and volumetric flowrates can be easily related by the ideal gas law. I'm planning using air at atmospheric pressure and temperatures 500-800 ##^\circ$## which I think justifies ideal gas law.

What I'm not clear about is when the tanks are opened and the flowrates are specified, what will determine the pressure in the system? This is important as I need to know and change the oxygen partial pressure during this experiment (electrical conductivity relaxation). The papers I've read about this method mention that change in oxygen partial pressure is induced by the change in the flowrate ratio (Dalton's law). This assumes that total pressure in the system is constant and therefore independent of the gas flowrates.

In another words, when the change in oxygen partial pressure is increased, why would nitrogen partial pressure decrease in this setup (or vice versa)? What mechanism is keeping the total pressure constant?

Schematic is provided to give a better insight into the process:
ECRPhoto.png
 
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  • #2
Dario56 said:
What mechanism is keeping the total pressure constant?
The gas outlet from the sample chamber, venting to the atmosphere.
 
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  • #3
Baluncore said:
The gas outlet from the sample chamber, venting to the atmosphere.
That makes sense as I didn't notice the crucial detail of the system being opened to the atmosphere through the venting pipe. In another words, total pressure in this setup is always atmospheric. By changing the ratio of mass flow rates of oxygen and nitrogen, we can change the oxygen partial pressure.
 
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FAQ: What determines the pressure inside this experimental setup?

What is the role of temperature in determining pressure?

Temperature plays a crucial role in determining pressure. According to the ideal gas law, pressure is directly proportional to temperature when the volume and the number of gas particles are constant. As temperature increases, the kinetic energy of the gas particles also increases, leading to more frequent and forceful collisions with the walls of the container, which raises the pressure.

How does the volume of the container affect the pressure?

The volume of the container is inversely related to pressure, as described by Boyle's Law. When the volume of a gas decreases while the amount of gas remains constant, the particles are forced closer together, resulting in more collisions with the walls of the container and an increase in pressure. Conversely, increasing the volume allows the gas particles to spread out, reducing the pressure.

What is the impact of the amount of gas present in the setup?

The amount of gas in a container directly affects the pressure according to Avogadro's Law. If the volume and temperature are held constant, increasing the number of gas particles will lead to an increase in pressure, as more particles result in more collisions with the container walls. Conversely, reducing the amount of gas will decrease the pressure.

How do external factors like altitude or atmospheric pressure influence the pressure inside the setup?

External factors such as altitude and atmospheric pressure can significantly influence the pressure inside an experimental setup. At higher altitudes, atmospheric pressure is lower, which can affect the pressure readings in a closed system. If the setup is open to the atmosphere, changes in external atmospheric pressure will directly impact the internal pressure of the system.

Can the presence of other gases in the setup change the pressure?

Yes, the presence of other gases can change the pressure in a given setup. According to Dalton's Law of Partial Pressures, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each individual gas. If additional gases are introduced to the system, they will contribute to the overall pressure, depending on their concentrations and temperatures.

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