Why does hot water clean dishes better than cold?

[bunny]

My niece asked me - I confidently began answering, then realised i didnt really have a clue.

[Splendour]

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.

[Borodog]

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.

[pzhon]

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.

[Cueballmania]

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.

[Daddys_Visa]

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.

[vhawk01]

[ 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.

[hexag1]

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?

[furyshade]

[ 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

[bunny]

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).