Why does water volume increase when heated?

In summary, the volume of water increases when heated past 4 degrees Celsius because the molecules move faster and bounce off each other with more energy, causing them to move away from each other and increase the volume. This is similar to how gases expand when heated, as explained by Charles's law.
  • #1
curioussoul09
2
0

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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  • #2
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.
 
  • #3
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

[tex]\frac{V_{1}}{T_{1}} = constant} [/tex] or V[tex]_{1}=T_{1}[/tex]
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:
  • #4
Wellesley said:
Charles's law - related to the gas laws

How is it related to the volume of liquid?
 

1. Why does water volume increase when heated?

Water volume increases when heated because the molecules in water gain energy and move faster, causing them to spread out and take up more space.

2. Does water always expand when heated?

No, water only expands when heated between 0°C and 4°C. When heated above 4°C, water starts to contract and become more dense.

3. How much does water expand when heated?

The expansion of water when heated depends on the initial temperature and the temperature it is heated to. On average, water expands by about 4% when heated from 20°C to 100°C.

4. Does the container affect the expansion of water when heated?

Yes, the container can affect the expansion of water when heated. If the container is rigid and does not allow for expansion, the pressure inside the container will increase. However, if the container is flexible, it will expand along with the water and the pressure will remain constant.

5. Can water volume decrease when heated?

Yes, water volume can decrease when heated above 4°C. At this point, the molecules in water start to move faster and the bonds between them start to break, causing the water to become less dense and take up less space.

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