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  #1  
Old 11-28-2007, 08:07 PM
bunny bunny is offline
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Default Why does hot water clean dishes better than cold?

My niece asked me - I confidently began answering, then realised i didnt really have a clue.
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Old 11-28-2007, 08:14 PM
Splendour Splendour is offline
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Default Re: Why does hot water clean dishes better than cold?

Actually heat kills germs bunny. Utensils in particular go into our mouths and the typical human mouth has 30+ bacterias in it plus cold germs, etc.

A dishwasher is particularly good because the intensity of the heat will kill more germs i.e. sterilization occurs.
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Old 11-28-2007, 08:25 PM
Borodog Borodog is offline
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Default Re: Why does hot water clean dishes better than cold?

I doubt that a dishwasher is hot enough to kill many bacteria. It's not like it's an autoclave.

Higher internal energy means that it is easier for the water molecules to penetrate food particles on the dishes and break them up. That's my guess, anyway.
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Old 11-28-2007, 08:36 PM
pzhon pzhon is offline
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Default Re: Why does hot water clean dishes better than cold?

My guess is that the primary reason is that substances dissolve faster at higher temperatures. It probably helps that the surface tension of hot water is lower than the surface tension of cold water. Water from condensation can also have a significant cleaning effect in a dishwasher with an ineffective spray, and there is a lot more condensation when the water is hot.
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Old 11-28-2007, 08:36 PM
Cueballmania Cueballmania is offline
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Default Re: Why does hot water clean dishes better than cold?

Solubility generally goes up as temperature rises. Water is polar and dissolves polar molecules. Soap is part polar part non-polar so it dissolves polar grease and washes away with water.
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  #6  
Old 11-28-2007, 08:38 PM
Daddys_Visa Daddys_Visa is offline
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Default Re: Why does hot water clean dishes better than cold?

I suspect it has a lot to do with dissolving the food particles and residue. Much of the grime on plates is water soluble, and as you know, things dissolve quicker in warmer water. Also most of the greasy residue will liquify at the higher temperatures, making it easier to rinse off.
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  #7  
Old 11-28-2007, 08:51 PM
vhawk01 vhawk01 is offline
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Default Re: Why does hot water clean dishes better than cold?

[ QUOTE ]
I suspect it has a lot to do with dissolving the food particles and residue. Much of the grime on plates is water soluble, and as you know, things dissolve quicker in warmer water. Also most of the greasy residue will liquify at the higher temperatures, making it easier to rinse off.

[/ QUOTE ]

Most of the grime on plates is NOT water soluble. Most of it is fat and grease.
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Old 11-29-2007, 12:48 AM
hexag1 hexag1 is offline
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Default Re: Why does hot water clean dishes better than cold?

ill take a stab:
The kinetic energy of all those hot water molecules is going to dislodge many more dirt particles off of the surface of dishes, when compared with the effect of cold water molecules.
Come to think of it, isn't temperature a measure of the root mean square momentum of the particles?
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Old 11-29-2007, 12:56 AM
furyshade furyshade is offline
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Default Re: Why does hot water clean dishes better than cold?

[ QUOTE ]
ill take a stab:
The kinetic energy of all those hot water molecules is going to dislodge many more dirt particles off of the surface of dishes, when compared with the effect of cold water molecules.
Come to think of it, isn't temperature a measure of the root mean square momentum of the particles?

[/ QUOTE ]

well, all those fats were probably hot at one point and liquid/gelatinous. if you reheat them they will probably go from the solid state to a more gelatinous one and be easier to get rid of
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  #10  
Old 11-29-2007, 01:05 AM
bunny bunny is offline
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Default Re: Why does hot water clean dishes better than cold?

Thanks all. I figured the higher energy thing had to be part of it, but wondered if there was a chemical component as well. (I speculated that maybe water and detergent mix better at higher temperatures based on brief experimentation).
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