• Question: Why does warm water get rid of grease better than cold water?

    Asked by lisaloo to Claire, Matt, Rob, Sam on 26 Jun 2013.
    • Photo: Robert Woolfson

      Robert Woolfson answered on 26 Jun 2013:


      The warm water has a bit more energy than cold water and so it’s easier for the warm water to break the bonds between the grease molecules and get rid of it.

      Although, if you go the other way round and add cold water to hot grease it has a slightly different result.

    • Photo: Sam Geen

      Sam Geen answered on 26 Jun 2013:


      Remember, temperature is the molecules and atoms in something moving around – in a solid, a higher temperature means the particles vibrate more, and in a gas or liquid they move around faster. So hotter water means the molecules can knock away grease particles more easily, and transfer energy to the grease so it moves away from the surface more easily. But still, soap helps a lot because it’s designed to stick to grease on one end of the molecule and water on the other, pulling the grease away with the water.

    • Photo: Claire Lee

      Claire Lee answered on 26 Jun 2013:


      Also, the fats and stuff we get from cooking have a melting point around 30-50 degrees C, and your hot water geyser is usually set to about 60 or more. So you’re actually melting the fat again and turning it into a liquid, which gets it off better.

      The soap then helps because it keeps the individual molecules apart.

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