Why does water volume increase when heated?

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SUMMARY

Water volume increases when heated past 4 degrees Celsius due to the kinetic energy of water molecules. As energy is applied, the molecules move faster and exert greater force on each other, causing them to move apart and occupy a larger volume. This phenomenon is explained by the principles of thermodynamics, where the average kinetic energy of the molecules increases with temperature, leading to expansion. Although Charles's law primarily applies to gases, the underlying concept of particle movement and energy transfer is relevant to understanding liquid water behavior.

PREREQUISITES
  • Understanding of thermodynamics principles
  • Familiarity with kinetic molecular theory
  • Knowledge of Charles's law and its limitations
  • Basic concepts of states of matter
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  • Research the kinetic molecular theory in detail
  • Explore the relationship between temperature and volume in liquids
  • Study the principles of thermodynamics related to phase changes
  • Investigate the behavior of water as a unique substance in terms of density and volume changes
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Students studying physics or chemistry, educators teaching thermodynamics, and anyone interested in the properties of water and its behavior 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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