Heat of vaporisation help please

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    Heat Vaporisation
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Discussion Overview

The discussion revolves around the heat of vaporization of water in comparison to its heat of fusion, specifically exploring the reasons behind the significant difference in energy requirements for these phase changes. The scope includes conceptual understanding of thermal properties and molecular interactions in different states of water.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant seeks an explanation for why the heat of vaporization is nearly seven times that of the heat of fusion for water, suggesting hydrogen bonding as a potential factor.
  • Another participant explains that converting ice to water requires less energy due to minimal changes in molecular proximity, while transitioning from liquid to vapor requires significantly more energy due to increased kinetic energy and freedom of movement.
  • A participant questions whether hydrogen bonding is the primary reason for the energy difference, noting that it exists in both liquid and solid phases but not in the gaseous state.
  • A later reply affirms that breaking hydrogen bonds is indeed a significant factor in the transition from liquid to gas, indicating that most attractive forces are disrupted during this phase change.

Areas of Agreement / Disagreement

Participants generally agree that hydrogen bonding plays a role in the energy required for phase changes, but there is some debate about the extent of its influence and the nature of molecular interactions in different states.

Contextual Notes

Participants have not fully resolved the implications of hydrogen bonding on the energy differences, and there may be additional factors influencing the heat of vaporization and fusion that are not discussed.

Benzeen
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Hi, i am writing a assignment about thermal expansion and contraction
and i would like to know if anyone could explain to me why the heat of vaporisation is nearly seven times that of the heat of fusion for water. I thought it might be hydrogen bonding but this is present in both the liquid and solid phases. any help is appreciated
 
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To convert ice to water not much energy is needed because there is not much change. Only the bonds or attractive force get weaker but molecules are still close together but in vapor phase molecules gains so much of kinetic energy that they are free to move all around the spaces and so we need to give much more energy.
 
but isn't it the hydrogen bonding that keeps the molecules close together in the first place? I mean, water in its liquid and solid states has hydrogen bonding but not in the gaseous state, so i thought that is why there is so much more energy needed to get it from liquid to gas, to break those bonds
 
yeah, you are correct. Most of the attractive force get ruptured while we get from liquid to gaseous state. Hydrogen bonding is also one among those forces.
 

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