Temp and Pressure measure of KE(average)

In summary, the conversation is about the interpretation of temperature and pressure in gases based on the kinetic molecular theory. It is stated that both temperature and pressure are proportional to the average translational kinetic energy of the gas molecules. The conversation then moves on to discussing an isothermal process where the temperature is kept constant, but the pressure increases. The confusion arises because, according to the kinetic molecular theory, if the average kinetic energy is constant, both temperature and pressure should be constant as well. However, it is explained that the process described is not possible as it is overconstrained. It is also mentioned that the pressure also depends on the density of the gas, which decreases as the gas expands during the isothermal process.
  • #1
Zahid Iftikhar
121
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Hi
My question is related to interpretation of temperature and pressure in gases on the basis of kinetic molecular theory.
According to it, both temperature and pressure are proportional to average translational kinetic energy of the gas molecules.
Now in a situation where an ideal gas in confined in a cylinder and is heated and it is an isothermal process i.e the temperature is kept constant. How is it possible to increase the pressure according to above stated rule. Now if temperature is constant, average KE should be constant which also determines the pressure. Where I am confused is , if average KE is constant, both temperature and pressure should be simultaneously constant. One of them can't be kept constant while the other changes.
Please help.
Regards
Zahid
 
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  • #2
Zahid Iftikhar said:
Hi
My question is related to interpretation of temperature and pressure in gases on the basis of kinetic molecular theory.
According to it, both temperature and pressure are proportional to average translational kinetic energy of the gas molecules.
Now in a situation where an ideal gas in confined in a cylinder and is heated and it is an isothermal process i.e the temperature is kept constant. How is it possible to increase the pressure according to above stated rule. Now if temperature is constant, average KE should be constant which also determines the pressure. Where I am confused is , if average KE is constant, both temperature and pressure should be simultaneously constant. One of them can't be kept constant while the other changes.
Please help.
Regards
Zahid
The process you are describing does not exist or rather is overconstrained. Isothermal heating is accompanied by expansion:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/isoth.html
 
  • #3
It's difficult to heat something while keeping the temperature constant ...
[edit] ah .. too late.
 
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  • #4
russ_watters said:
The process you are describing does not exist or rather is overconstrained. Isothermal heating is accompanied by expansion:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/isoth.html
russ_watters said:
The process you are describing does not exist or rather is overconstrained. Isothermal heating is accompanied by expansion:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/isoth.html
Yes it is isothermal expansion process. The cylinder I mentioned is fitted with frictionless piston and it moves up with more heat added to the working substance and hence does work. My question relates to keeping temperature constant and increasing the pressure. As average KE determines both the temperature and the pressure, how is it possible to change one and fix other.
High regards for your reply.
Zahid
 
  • #5
Zahid Iftikhar said:
The cylinder I mentioned is fitted with frictionless piston
Nice to know... :rolleyes: And @russ_watters' link says it all: Q=W
 
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  • #6
The pressure depends on the average KE but not only on it. If you look up the actual formula, it depends on the density of the gas too (number density, n, for example). So as the gas expands n decreases and so does the pressure. At unchanged average KE per molecule.
 
  • #7
nasu said:
The pressure depends on the average KE but not only on it. If you look up the actual formula, it depends on the density of the gas too (number density, n, for example). So as the gas expands n decreases and so does the pressure. At unchanged average KE per molecule.[/QUOTE
Yes, that is the point I am missing. The density does play a role in it as it does not remain constant.
Thanks.
 

1. What is the relationship between temperature and the average kinetic energy of particles?

The temperature of a substance is directly proportional to the average kinetic energy of its particles. This means that as the temperature increases, the average kinetic energy of the particles also increases.

2. How does pressure affect the average kinetic energy of particles?

Pressure is a measure of the force exerted by particles on the walls of their container. As the pressure increases, the average kinetic energy of the particles also increases. This is because the particles are colliding with the walls of their container more frequently and with greater force.

3. What units are used to measure temperature and pressure?

Temperature is typically measured in degrees Celsius or Kelvin, while pressure is measured in units of force per unit area, such as Pascals, atmospheres, or pounds per square inch.

4. How does the temperature and pressure of a substance affect its phase?

The temperature and pressure of a substance have a significant impact on its phase or state of matter. For example, increasing the temperature and pressure of a solid can cause it to melt into a liquid, and further increases can turn it into a gas.

5. How do scientists measure the average kinetic energy of particles in a substance?

Scientists use various methods to determine the average kinetic energy of particles in a substance, such as using a thermometer to measure temperature or using instruments like a barometer or manometer to measure pressure. They may also use mathematical equations and models to calculate the average kinetic energy based on the substance's temperature and pressure.

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