Intensive Properties of a system- density

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Discussion Overview

The discussion revolves around the concept of density as an intensive property in thermodynamics. Participants explore the relationship between mass, volume, and density, questioning how density can remain constant despite changes in mass and volume, which are both extensive properties.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how density can be considered an intensive property if it is calculated as mass divided by volume, suggesting a potential error in understanding.
  • Another participant clarifies that density would only increase with mass if volume is held constant.
  • A participant expresses confusion about density fluctuating with changes in mass or volume, noting that both mass and volume are extensive properties.
  • One participant explains that taking the ratio of two extensive quantities typically results in an intensive quantity, indicating that doubling mass and volume cancels out the factors when calculating density.
  • Another participant shares a conceptual approach of visualizing an object and considering whether its density changes when cut in half, suggesting this helps in understanding the concept of density as an intensive property.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the nature of density as an intensive property, with some clarifying points while others remain confused about the implications of mass and volume changes. No consensus is reached on the initial confusion regarding density's classification.

Contextual Notes

Participants highlight the dependence on definitions of intensive and extensive properties, and the discussion does not resolve the initial confusion about density's classification.

leah3000
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How is density an intensive property?

If density= mass/ volume

wouldn't the density increase as the mass increases seeing that they are directly proportional?

I'm seeing this in my Uni lecture slides on thermodynamics; that density is an intensive property which means it is mass independent but I don't understand that. Is it an error? Or am I thinking of this in the wrong way?
 
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leah3000 said:
wouldn't the density increase as the mass increases seeing that they are directly proportional?

Only if you would be able to keep the volume constant.
 
Borek said:
Only if you would be able to keep the volume constant.

Ok so i understand that part, but won't the density still fluctuate more or less once the mass or volume is altered?

I guess I'm confused a bit because both mass and volume are extensive properties...so why is density intensive?
 
Usually if you take the ratio of two extensive quantities, you will get an intensive quantity. If you double the mass, you also double the volume so the factors of two cancel out when you take the ratio, and density remains the same.
 
I was taught to imagine the object and then cut it in half and ask yourself if that property has changed. Makes it pretty simple to see how a block of iron, for example, will have the same density as the two blocks you can make by cutting the original in half.

Its not a rigorous mathematical proof, but it helps clear things up when you're unsure.
 

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