Thermodynamics question about density

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    Density Thermodynamics
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Discussion Overview

The discussion revolves around the relationship between density, heat capacity, and thermal energy in objects of the same volume. Participants explore how these factors interact, particularly in the context of solids and gases, and consider practical implications related to material properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants propose that if one object is twice as dense as another of the same volume, it might contain roughly twice as much heat energy at the same temperature.
  • Others argue that this relationship depends on the heat capacities of the materials involved.
  • A participant suggests that doubling density while keeping volume constant may lead to doubling heat capacity, particularly for ideal gases, but expresses uncertainty regarding non-ideal gases.
  • Another participant notes that inter-molecular forces could significantly affect heat capacity, especially in solids.
  • One participant clarifies that their understanding of "object" encompasses any arrangement of molecules, not limited to solids or gases, and discusses the implications of molecular momentum on thermal energy.
  • A later reply acknowledges the complexity of the assumptions involved in the initial responses and suggests that the relationship may not be straightforward.
  • Practical considerations are introduced regarding the cost of fuel for producing foam glass, which has a different density than solid glass.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between density, heat capacity, and thermal energy, indicating that multiple competing perspectives remain. The discussion does not reach a consensus on the implications of density on heat capacity across different materials.

Contextual Notes

Limitations include assumptions about material behavior under varying conditions, the dependence of heat capacity on molecular structure, and the lack of resolution regarding the applicability of ideal gas behavior to non-ideal gases.

Jay Lakoda
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If an object is twice as dense as another object of the same volume, would the more dense object be able to contain roughly twice as much heat energy, given that the temperature was the same in each?
 
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Roughly yes.
 
Doesn't it also depend on the heat capacities of the materials?

Chet
 
Chestermiller said:
Doesn't it also depend on the heat capacities of the materials?

Chet

I think the OP is actually simply asking about the heat capacities. His question is basically "if I double the density, keeping the volume constant, do I double the heat capacity?". If I recall correctly, this should be true for an ideal gas. I'm not sure if it's still true for a non-ideal gas, which is why I said "roughly".
 
Matterwave said:
I think the OP is actually simply asking about the heat capacities. His question is basically "if I double the density, keeping the volume constant, do I double the heat capacity?". If I recall correctly, this should be true for an ideal gas. I'm not sure if it's still true for a non-ideal gas, which is why I said "roughly".
When he said "object", I naturally assumed he was talking about solids.
 
Chestermiller said:
When he said "object", I naturally assumed he was talking about solids.

Ah, in that case, I'm not sure. I would think the inter-molecular forces would affect the heat capacity greatly. I'm an astrophysicist, so everything is an ideal gas to me... :D
 
Please compare heat capacities of He and Xe.
 
Bystander said:
Please compare heat capacities of He and Xe.

Ah you are right, I was thinking of doubling the density being doubling the number of atoms not doubling the mass of the atoms. @Jay Lakoda : neglect my first answer, it has too many assumptions in it to be useful.
 
Thanks for the replies. By "object" I just meant a clump of molecules in any arangement. Not necessarily a solid or a gas. I'm looking at it this way: molecules are bouncing around in object #1. The average speed of the molecules is its temperature, which is the same as object #2. But object #2 is twice as dense. The heavier molecules of object #2 are moving at the same speed as object #1, but they have twice the momentum which is thermal energy. Of course there are lots of variables that slight alter things, but that's why I used the term "roughly."

But I'm asking the question because I want to confirm that my understanding is correct.

And more practical speaking, what I want to know is how much money would the fuel cost to produce 4,000 cubic feet of foam glass (which has a much smaller density than solid glass.)
 

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