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Chemistry: what exactly happens when an ice cube melts in warm water?When analyzing an...

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mballaz | (Level 3) eNoter

Posted September 18, 2010 at 1:17 AM via web

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Chemistry: what exactly happens when an ice cube melts in warm water?

When analyzing an ice cube melting in warm water, what exactly is happening at a molecular level? what about the bonds of the molecules as the temperature rises? what are potential and kinetic energies? and how do they relate to the melting ice?

How can someone determine the molar heat of vaporization of water with the use of an experiment?


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nessus | High School Teacher | (Level 2) Adjunct Educator

Posted July 10, 2011 at 4:04 PM (Answer #1)

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According to kinetic theory particles (atoms, molecules) are in constant thermal motion unless at absolute zero. Molecules of water have attraction forces between them, and if the molecules aren't moving much i.e. they are very cold, the forces can bond the molecules together - you have ice. When you put ice into (warmer) liquid water the molecules in the ice begin to move (actually a type of wobbling) more and more until the bonds are broken and the ice melts.

At a deeper level, just at the temperature when the bonds get broken the molecules move slightly further apart without wobbling more even though the attractive forces are still there. This is analogous to lifting something higher above the Earth - you give it potential energy. The potential energy to do this has come from the warm water. The energy needed to do this is called latent heat. After the molecules break apart any extra energy causes the molecules to wobble faster - they have gained kinetic energy.

To find the molar heat of vaporization of water take 18 grams of water and heat it just to boiling point. Then continue heating with a heater that can have its energy output measured. Keep heating until all of the water has boiled away. The energy supplied by the heater to cause the boiling only is the molar heat of vaporization of water.

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