Determining concentration by measuring pressure change

In summary, the conversation discusses deriving an equation for calculating concentration by measuring pressure change in a known volume. The known data includes pressure change, volumetric flow rate, total pressure, and temperature. The attempt at a solution involves using the ideal gas law and mass volume rate equations, but the correct numerical concentration is not obtained. There may be missing information or a mistake in the solution.
  • #1
Boltzano
2
0

Homework Statement


Derive an equation how one can calculate concentration by measuring pressure change in a known volume.

Known data:
Pressure change dp/dt in a known volume V, volumetric flow rate F, total pressure p and temperature T.


Homework Equations


Probably ideal gas law pV=NkT and mass volume rate (throughput) Q=Fp=d(pV)/dt



The Attempt at a Solution


Not really sure how to solve this since this was not an textbook question but actual measurment so I'm not sure about the needed equations. But I would start:

d(pV)/dt=V*dp/dt=Q=Fp (since V is constant)

=> V*dp/dt=(Nkt/p)*(dp/dt)=Fp

=>N=(Fp^2/kT)*(dt/dp)

But doing so I end up with number of molecules and not concentration. This could easily be solved by dividing with known volume V but for some reason I won't get right numerical concentration (in measurments computer program calculated the concentration automatically from known data).
 
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  • #2
Was there some information missing or is this just too simple so people won't bother =D

Somehow my solution just doesn't seem right. Is it ok to take out the V from d(pV)/dt and then substitute with NkT/p?
 

1. How does measuring pressure change help determine concentration?

When a chemical reaction occurs, it often produces or consumes gases. By measuring the pressure change caused by the gas, we can determine the rate at which the reaction is occurring, which can then be used to calculate the concentration of the reactants or products involved.

2. What equipment is needed to measure pressure change?

To measure pressure change, a manometer or pressure sensor is typically used. This device measures the difference in pressure between two points, allowing for accurate measurements of pressure changes.

3. Is measuring pressure change a reliable method for determining concentration?

Yes, measuring pressure change is a widely used and reliable method for determining concentration in various chemical reactions. It is especially useful for reactions involving gases, as the pressure change can be directly correlated to the amount of gas present.

4. Can pressure change be used to determine concentration in all types of reactions?

No, pressure change can only be used to determine concentration in reactions that involve gases. Reactions involving only liquids or solids do not produce measurable pressure changes and therefore cannot be analyzed using this method.

5. What are some potential sources of error when using pressure change to determine concentration?

Potential sources of error can include leakage of gas from the reaction chamber, temperature fluctuations affecting the pressure readings, and human error in measuring and recording the pressure values. It is important to carefully control these variables in order to obtain accurate results.

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