Finding the Volume of an Ideal Gas

Click For Summary

Homework Help Overview

The discussion revolves around finding the volume of an ideal gas using different approaches, specifically the ideal gas law and density calculations. The participants are exploring the implications of varying air density due to temperature and pressure on their calculations.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to solve the problem using both the ideal gas equation and a density-based approach, leading to different volume results. Questions are raised about the validity of the density approach and the impact of varying air density.

Discussion Status

Participants are actively engaging with the problem, questioning the assumptions related to air density and its variability. Some guidance has been offered regarding the importance of using the correct values for temperature and pressure, and hints have been provided about potential issues with units rather than numerical values.

Contextual Notes

There is a mention of a marking scheme that suggests a specific answer, which raises questions about the correctness of the units used in the calculations. The discussion highlights the need to consider the conditions under which the density of air is measured.

Kajan thana
Messages
149
Reaction score
18
Homework Statement
A rigid tank contains 5 kg of air at 100 kPa and 27 °C. The air is now heated until
its pressure doubles. Determine the volume of the air?
Relevant Equations
1) PV= mRT.
2) Denisty = Mass/Volume
Hi,

I tried to do this question in two different approaches one of them was using the equation PV=mRT where I got the right answer which is 4.305 m**2. However, I tried using this Density = Mass/Volume, where I substituted Denisity= 1.225 and Mass equals 5kg to get the volume as 4.08.
Can someone tell me why I can't use the second equation? Is it because the density of the air varies?
 
Physics news on Phys.org
Kajan thana said:
Is it because the density of the air varies?
Yes. The density of air will vary with temperature and pressure. You are given values for both and should use those values.

The volume of the air is most definitely not 4.305 m2. Can you see why?
 
  • Like
Likes   Reactions: Kajan thana
jbriggs444 said:
Yes. The density of air will vary with temperature and pressure. You are given values for both and should use those values.

The volume of the air is most definitely not 4.305 m2. Can you see why?
Thank you.
It makes sense that the density will vary with temperature and pressure so I have to use the values that is given. But can please explain why 4.305m2 is not also the right answer ( according to marking scheme, it is ) ?
 
Last edited:
Hint: the problem is not with the number, but the units.
 
  • Like
Likes   Reactions: Kajan thana and jbriggs444
mjc123 said:
Hint: the problem is not with the number, but the units.
Oh thank you.. Yh wrong unit..
 

Similar threads

Incompatibility between ideal gas equations of state
  • · Replies 2 ·
Replies
2
Views
2K
Trouble solving for end state of two control volumes in a rigid tank
  • · Replies 12 ·
Replies
12
Views
3K
Ideal Gas Law and Pressure at 80°C
  • · Replies 2 ·
Replies
2
Views
3K
Calculate ideal-gas temperature of a material
  • · Replies 2 ·
Replies
2
Views
2K
Changes in pressure, temp, & entropy of ideal gas in atmosphere
  • · Replies 10 ·
Replies
10
Views
2K
Proof question related to the Ideal Gas Law
  • · Replies 8 ·
Replies
8
Views
2K
Closed cycle of an ideal gas
  • · Replies 3 ·
Replies
3
Views
2K
Verification of ideal gas law experiment
  • · Replies 5 ·
Replies
5
Views
2K
What would be a real-life example of the ideal gas law?
  • · Replies 3 ·
Replies
3
Views
10K
Mixing two ideal gases with different V, T at constant pressure
  • · Replies 16 ·
Replies
16
Views
4K