# Homework Help: Why does water volume increase when heated?

1. Mar 24, 2009

### curioussoul09

1. The problem statement, all variables and given/known data
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!

2. Mar 25, 2009

### ThalorB

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. Mar 26, 2009

### Wellesley

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: Somehow I missed that the question was about liquid water. Sorry.....
Charles's law is not related to liquids...thanks Borek.

Last edited: Mar 26, 2009
4. Mar 26, 2009

### Staff: Mentor

How is it related to the volume of liquid?