Butane vs Pentane: Which is Liquid & Why?

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Discussion Overview

The discussion revolves around the physical states of butane and pentane at room temperature, specifically which compound is a liquid and the reasons behind their differing states. It includes considerations of molecular mass, intermolecular forces, and kinetic energy.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes that pentane is the liquid due to its higher mass, suggesting that a higher mass correlates with a higher melting point.
  • Another participant questions the sufficiency of the explanation regarding greater mass and its impact on molecular interactions.
  • A participant suggests that as molecular mass increases, the strength of dispersion forces also increases, requiring more energy to weaken molecular attraction, which could explain higher boiling points.
  • There is a query about the relationship between higher mass and higher dispersion forces, prompting further exploration of the role of electrons.
  • One participant notes that larger molecules have the same kinetic energy as smaller ones at a given temperature but possess more surface area for intermolecular forces to act upon.

Areas of Agreement / Disagreement

Participants express varying degrees of agreement on the relationship between molecular mass and dispersion forces, but the discussion remains unresolved regarding the specific mechanisms and implications of these interactions.

Contextual Notes

Participants have not fully clarified the assumptions regarding the relationship between molecular mass, electron count, and dispersion forces. The discussion also does not resolve the implications of kinetic energy on molecular interactions.

magma_saber
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Homework Statement


There are two compounds, butane and pentane. one is a liquid at at room temp and the other is gas. which is a liquid and why?

Homework Equations





The Attempt at a Solution


I'm guessing that its pentane. For a gas to liquify, it should have a have a higher melting point, meaning that it has a higher freeing point. They both only have london dispersion forces but pentane has a greater mass so it should have a higher melting point.
 
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More or less correct, although I am not sure if mentioning just 'greater mass' will do. Why do molecules of greater mass interact stronger?
 
im guessing as the mass of the molecules increases, so does the strength of the dispersion force acting between the molecules, so more energy is required to weaken the attraction between the molecules resulting in higher boiling points.
 
OK, but why higher mass means higher dispersion forces?

Hint: higher mass - more electrons, or less electrons?
 
magma_saber said:
im guessing as the mass of the molecules increases, so does the strength of the dispersion force acting between the molecules,.

it also means that the molecules move more slowly at any given temp
 
so since there are more electrons, higher dispersion forces?
 
Yes.
 
thanks for all the help.
 
larger molecules have the same kinetic energy as smaller molecules at a given temp but they have more surface area for intermolecular forces to act upon.
 

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