Why does water volume increase when heated?

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Discussion Overview

The discussion revolves around the phenomenon of water volume increasing when heated past 4 degrees Celsius, focusing on the molecular explanation for this behavior. Participants explore theoretical concepts and seek clarification on the underlying principles governing this change in volume.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant notes that water molecules move quicker when energy is applied, questioning why this necessitates an increase in volume rather than just faster movement within the same space.
  • Another participant suggests a thought experiment involving people dancing to illustrate how increased energy can lead to greater spatial occupation.
  • A participant references Charles's law and the Ideal gas law, explaining that as temperature increases, volume typically increases due to faster particle movement and increased kinetic energy, although they later acknowledge that this law does not apply to liquids.
  • There is a request for clarification on how Charles's law relates to the volume of liquid water, indicating a need for further exploration of the topic.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the application of gas laws to liquids, with some confusion about the relationship between temperature, energy, and volume in the context of liquid water. No consensus is reached on the explanation for the volume increase.

Contextual Notes

Participants highlight the distinction between gas and liquid behavior, indicating that assumptions about gas laws may not directly apply to liquids like water. There is also a recognition of the need for a molecular-level explanation that remains unresolved.

Who May Find This Useful

This discussion may be of interest to students studying thermodynamics, those curious about the properties of water, or individuals seeking to understand the molecular behavior of substances under varying temperatures.

curioussoul09
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Homework Statement


Why does water volume increase when heated past 4 degrees Celsius?

2. The attempt at a solution
I know that water molecules move quicker when energy is applied (e.g. heat), but I don't understand why the volume of water must increase. Why can't water molecules just move quicker in the same amount of space? I need a molecular explanation. Thanks!
 
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Hello, and welcome to PF.

A simple thought experiment may help to clarify this for you. Consider a group of people standing shoulder-to-shoulder and the floor area they occupy. Now, give them sugar (energy) and have them dance to fast-tempo music (~boiling). Consider the floor area they would then occupy.
 
curioussoul09 said:
I know that water molecules move quicker when energy is applied (e.g. heat), but I don't understand why the volume of water must increase. Why can't water molecules just move quicker in the same amount of space? I need a molecular explanation. Thanks!


Charles's law - related to the gas laws, and the Ideal gas law (PV=nRT), explains that

\frac{V_{1}}{T_{1}} = constant} or V_{1}=T_{1}
Why gases expand:
When temperature goes up, so does volume.

Why all states of matter expand with energy:
When energy is added, the particles move faster and bounce off the container harder. The average kinetic energy of each molecule increases as the temperature goes up. As a result, the particles move away from each other, causing the volume to increase.

EDIT: :bugeye: Somehow I missed that the question was about liquid water. Sorry...
Charles's law is not related to liquids...thanks Borek.
 
Last edited:
Wellesley said:
Charles's law - related to the gas laws

How is it related to the volume of liquid?
 

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