Effect of density on rms speed in ideal gas eqn

In summary, the conversation discusses the relationship between density and root mean square speed in the context of constant pressure and temperature. The second equation suggests an inverse relationship between the two, but the question specifically mentions constant temperature. This is proven by the fact that the equation for kinetic energy is directly proportional to temperature and does not include density.
  • #1
toforfiltum
341
4

Homework Statement


upload_2016-4-2_18-24-3.png

upload_2016-4-2_18-24-33.png


Homework Equations


1) PV = nRT
2 )## P = ⅓ ρ<c^2> ##
3) KE ∝ T

The Attempt at a Solution


According to the second equation above, density is inversely proportional to root mean square speed at constant pressure, but the answer states that the root mean square speed depends only on the temperature so the answer is no effect.

I don't see how when the second equation suggests otherwise. Can someone help me out?
 
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  • #2
toforfiltum said:
According to the second equation above, density is inversely proportional to root mean square speed at constant pressure
Yes, but the question states constant temperature, not constant pressure.
 
  • #3
haruspex said:
Yes, but the question states constant temperature, not constant pressure.
Oops, how could I misread that. Thanks.
So to prove this, it is ## \frac {1} {2} Nm<c^2> = \frac{3} {2} NkT ## ? Which is KE ∝ T?
Since ρ is not in the above equation, it is proven that density has no effect on root mean square speed?

Thanks!
 
  • #4
toforfiltum said:
Oops, how could I misread that. Thanks.
So to prove this, it is ## \frac {1} {2} Nm<c^2> = \frac{3} {2} NkT ## ? Which is KE ∝ T?
Since ρ is not in the above equation, it is proven that density has no effect on root mean square speed?

Thanks!
Ok.
 

Related to Effect of density on rms speed in ideal gas eqn

1. What is the ideal gas equation?

The ideal gas equation, also known as the perfect gas law, is a mathematical formula that describes the relationship between the pressure, volume, temperature, and number of moles of an ideal gas. It is expressed as PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature.

2. How does density affect the rms speed of particles in an ideal gas?

According to the ideal gas equation, the rms (root-mean-square) speed of particles in an ideal gas is directly proportional to the square root of the temperature and inversely proportional to the square root of the molar mass. As density is directly proportional to the number of moles and inversely proportional to the volume, an increase in density would lead to a decrease in the rms speed of particles.

3. Why is the rms speed of particles important in studying the behavior of gases?

The rms speed of particles in a gas is a measure of their average kinetic energy. This is important because it helps us understand the behavior of gases, such as their pressure, temperature, and volume, which are all related to the kinetic energy of particles. The rms speed also helps in determining the rate of diffusion and effusion of gases.

4. How does the ideal gas equation account for the effect of density on rms speed?

The ideal gas equation accounts for the effect of density on rms speed by incorporating the molar mass and volume of the gas into the equation. As mentioned before, an increase in density leads to a decrease in the volume, which in turn decreases the rms speed of particles according to the equation. This relationship is also confirmed by experimental data.

5. Is the effect of density on rms speed the same for all gases?

No, the effect of density on rms speed may vary for different gases depending on their molar mass. The ideal gas equation shows that the rms speed is inversely proportional to the square root of the molar mass of the gas. Therefore, gases with a lower molar mass will have a higher rms speed compared to gases with a higher molar mass, when all other variables are constant.

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