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The answer is as close to your kitchen sink!  Next time you have dinner, fill one sink with cold water and the other with hot water. See which cleans faster and better. Even if you try to compensate with a surplus of soap the hot water sink will be much more effective...it's due to the molecules that make up the water. These tiny molecules are in constant motion and with water, the hotter it gets the faster they move.
Svante A. Arrhenuis (1859-1927), a Swedish Chemist, researched the heat-energy relationship and determined that higher temperatures cause molecules to collide with each other creating energy that can cause the molecules of grease and grime to break free from the surface they are attached to. Hot water improves cleaning by substantially lowering the surface tension.
There are three key elements to the cleaning triangle: 1) Heat, Agitation (pressure), and Soap. The more heat you have the less you have to compensate with high pressure or excessive chemicals that may damage your surface.Also, the heated water accelerates the chemical reaction.For every 50 F degree increase in temperature, the activity and effectiveness doubles!!
Higher temperatures cause much greater emulsification of oils, grease, and mold. Like the dishes in your sink, hot water cuts grease, grime, and mold, while cold water only pushes it around. Heat eliminates mold spores while cold water can actually enhance their growth.
                  - Cleaner Times, May 2009
