Why is CO2 liquid less dense than CO2 solid

In summary, Gallium is less dense in the liquid state because the solid form (ice) is less dense than the liquid form.
  • #1
bobsmith76
336
0
I can sort of understand why water is denser than ice, but for CO2 I cannot understand why it is the other way around. Here is my best shot at understanding it: I imagine H2O's solid structure as a hexagon due to the hydrogen bonds, where each point represents one atom. When these bonds are broken the six line segments separate from each other and now the liquid is just a compilation of these six line segments which is more dense. I imagine a CO2 solid as a set of squares fixed together. When it turns into a solid those squares remain in tact thus the substance does not become more dense.

Does this sound right?
 
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  • #2
As a practical matter, water is the exception. Almost all substances are denser as solids in comparison to liquids.
 
  • #3
From: http://wiki.answers.com/Q/What_subs...a_solid_state_than_they_are_in_a_liquid_state


In addition to water, for which the solid form (ice) is less dense than the liquid form, the element Gallium is also less dense in the liquid state. Gallium can be solid at room temperature but will melt in the hand.
== Less Dense in Solid Form ==

confirmed as solid less dense than liquid:


gallium - 5.91 (solid) vs 6.095 (liquid)
bismuth - 9.78 (solid) vs 10.05 (liquid)
germanium - 5.323 (solid) vs 5.60 (liquid)
silicon - 2.3290 (solid) vs 2.57 (liquid)
water - 0.917 (solid) vs 0.998 (liquid)

claimed but probably false:


acetic acid - 1.266 (solid) vs 1.049 (liquid)
antimony - 6.697 (solid) vs 6.53 (liquid) (this "error" is repeated in many places, inc wikipedia)
Water is not always less dense in solid form. Depending on how the water crystals are formed, it may actually be more dense. Examples include HDA and VHDA.



Read more: http://wiki.answers.com/Q/What_subs...than_they_are_in_a_liquid_state#ixzz1BFSglL6f
 
  • #4
I'm not worried about the statistics of density, I want to know why.
 

1. Why is CO2 liquid less dense than CO2 solid?

CO2 (carbon dioxide) is a unique compound that exists in different physical states at different temperatures and pressures. At atmospheric pressure, CO2 solid (dry ice) has a higher density than CO2 liquid. This is due to the molecular arrangement of CO2 solid, which forms a tightly packed lattice structure compared to the more loosely arranged molecules in CO2 liquid.

2. How does temperature affect the density of CO2 solid and liquid?

In general, as temperature decreases, the density of a substance increases. This is because colder temperatures cause molecules to move more slowly and pack more closely together. However, CO2 is an exception to this rule. At atmospheric pressure, the density of CO2 solid decreases as temperature decreases, while the density of CO2 liquid increases as temperature decreases.

3. Why does CO2 solid sublimate (change directly from a solid to a gas) instead of melting into a liquid?

CO2 has a unique phase diagram, meaning the conditions at which it exists as a solid, liquid, or gas are different from most other substances. At atmospheric pressure, the temperature at which CO2 can exist in a liquid state is below its freezing point, so it will sublimate instead of melting. This is why solid CO2 (dry ice) will turn directly into a gas without going through a liquid phase.

4. Can the density of CO2 liquid and solid be changed?

Yes, the density of CO2 liquid and solid can be altered by changing the temperature and pressure. At higher pressures, the density of CO2 liquid increases and the density of CO2 solid decreases. Similarly, at lower temperatures, the density of CO2 liquid increases and the density of CO2 solid decreases.

5. What are the practical applications of understanding the difference in density between CO2 liquid and solid?

Understanding the difference in density between CO2 liquid and solid is important in various industries, such as food preservation, where dry ice is often used. It is also relevant in the study of climate change, as CO2 is a major greenhouse gas and its density can affect its behavior in the Earth's atmosphere. Additionally, the unique properties of CO2 make it useful in applications such as dry cleaning and fire extinguishers.

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