This document discusses the Mpemba effect, where hot water can freeze faster than cold water. It explains that water exists in three states - gas, liquid, and solid (ice) - depending on the strength of molecular connections. Hot water has more kinetic energy, allowing molecules to form stronger connections into ice faster when cooled compared to slower cold water molecules. Therefore, contrary to intuition, hot water can freeze before cold water despite starting at a higher temperature.

1. Mpemba Effect
Why does hot water freeze faster
than cold water

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. • Thank you for taking some of your time
to read this presentation 
By: Deni Munjas