How Quickly Does an Ideal Gas Expand with Temperature Change?

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Discussion Overview

The discussion revolves around the expansion of an ideal gas in response to a temperature change, specifically examining how quickly this expansion occurs when a gas is heated from 30 degrees to 50 degrees in a balloon. The scope includes theoretical considerations and applications of the ideal gas law.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant requests an equation to determine the rate of expansion of an ideal gas during a temperature change.
  • Another participant suggests using the ideal gas law (PV = nRT) to understand the relationship between pressure, volume, and temperature, noting that expansion occurs as temperature increases but does not specify a time frame for this process.
  • A different participant questions the applicability of the ideal gas law, stating it is valid for static systems and implying that the time taken for expansion depends on how long it takes the system to re-equilibrate.
  • Another participant proposes considering diffusion, indicating that the diffusion rate is inversely proportional to molecular mass, suggesting an alternative perspective on gas expansion.
  • One participant calculates the partial derivative of volume with respect to temperature, suggesting that under constant pressure and amount of gas, the rate of expansion is constant.
  • Another participant connects this to Guy-Lussac's law, stating that volume is directly proportional to temperature under constant pressure and amount of gas, and relates this to the earlier derivative expression.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gas expansion, with some focusing on the ideal gas law and its implications, while others raise questions about the assumptions of static systems and the role of diffusion. There is no consensus on the specifics of how quickly the gas expands or the best approach to quantify this process.

Contextual Notes

Limitations include the assumption of constant pressure and the number of moles of gas, as well as the potential impact of dynamic versus static conditions on the applicability of the ideal gas law.

daniel3777
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can anyone give me an equation for the rate that an ideal gas expands in a temperature change. like when a gas goes from 30 degrees to 50 degrees in a balloon. how quickly would it expand?
 
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you need to use the ideal gas law to figure it out.
Let P be the pressure of a gas, V the volume it occupies, and T its temperature (which must be in absolute temperature units, i.e., in Kelvin). Then the ideal gas law states

PV = nRT


where n is the number of moles of gas present and R is the universal gas constant, or equivalently


it would expand to the new volume as the gas temperature inccreases, there isn't a real amount of time it takes to expand, it just expands as the temperature increases. if the temperature were to suddenly increase by 20 degrees, then the gas would suddenly expand to the the new volume, but normaly it would be a gradual process because the temperture increasing is a gradual process.
 
Well, the ideal gas law is only valid for static systems, right? So I guess the answer would be that it would take as long as was needed for the system to re-equilibrate at the new parameters.
 
Maybe you can try to use diffusion alternative... Diffusion rate changes in an indirectly proportional way with the molecular mass.
 
It seems to me that you would have to take the partial derivative of Volume with respect to T so you would get dV/DT=nR/P. So if pressure and amount of gas is held constant, the rate at which it expands is constant.
 
Last edited:
This is basically the same thing that Guy-Lussac's law says. V=kT where k is some constant. So for example, if T doubles then volume will double (only if pressure and the amount of gas is held constant). Writing dV/dT=nR/P is just a more "sophisticated" way of stating the same thing.
 

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