Published on August 17, 2012
Mpemba EffectWhy does hot water freeze faster than cold water
Repeating the basics• Water has 3 alotropic states• Gas, liquid, solid a.k.a ice• The difference between those states is in the strength of their connections that exist between the H2O molecules
Alotropic state - gas• The connections between the H2O molecules are almost non existent• Water will be in it’s gassy state when it’s temperature is above 100ºC
Alotropic state - Liquid• The connections between the H2O molecules in liquid water are stronger than in gassy water but still not strong enough for the water to be solid• Water is liquid when it’s temperature is between 0 and 100ºC
Alotropic state - Ice• The connections between the H2O molecules in ice are much stronger than in any other state, so strong that they make ice solid• Water is in it’s icy state when it’s temperature is below 0ºC
Connections• Water changes it’s states by weaking (even breaking) or strengthening (even creating) it’s connections between the H2O molecules• Basic chemistry tells us that in order to create such connections we need to invest energy in them, by breaking them we will release the same energy we stored in them earlier• Therefore in order to understand the freezing itself we need to be aware of everything that is going on between the H2O molecules during that process
Freezing• Freezing occurs when we lower the temperature of T/ ºC the water to (not below) 0ºC• At that point no matter how much we try to freeze water it’s liquid temperature won’t drop below 0ºC until every bit 0 of it is frozen solid t/sec• In short there is no liquid Ice water below the 0ºC
Lowering the temperature• When you lower the temperature of the water, the energy that water posseses or as some people call it heat will be transfered to the body that is freezing it• Some of that energy will also be used to create solid state ice connections between the H2O molecules, as we said earlier the connections between the molecules in ice are much stronger than in liquid water, those connections need to be created at some point
Why does hot water freeze faster than cold water ?• Hotter particles move faster than cold particles (molecules in this example)• Therefore we know hot water posseses more kinetic energy than cold water• So hot water unlike cold water will be able to create solid state ice connections between the H2O molecules much faster because it will simply have more energy to do so while we lower it’s temperature• More energy, more connections between molecules
Conclusion• The scale from 100ºC to 0ºC is not a path and it should not be percieved as a path• Just because one glass of water is at 4ºC that doesn’t mean it is “close” to becoming ice, it means that the particles in that water don’t move as fast as particles in hot water• That is why hot water will freeze faster than cold water
• Thank you for taking some of your time to read this presentation By: Deni Munjas
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