What is the difference between a glass of water and your foggy breath on a winter's day?  What is the difference between an icicle dangling from a roof and the steam shooting out of a tea kettle?  The answer?  Not much.  They are all water in different states.  Making something very hot or very cold will not change what it is.  Just as you are the same person if you are sweating as you are when your teeth are chattering.  It takes a great deal more to change something completely.


So wait wait wait . . .  How is an icicle like a glass of water and how is that like your foggy breath on a cold day?  You know that if an icicle gets warm enough it will turn into a puddle of water.  If you get that water hot enough it will begin to steam like your breath when it's cold outside.  A physical change happens when something changes the way it looks but does not change how it reacts with other things.  Even though the water is changing, its smallest parts stay the same.  This kind of change can be as simple as crushing a can.  There can be more to it, though.  If we look at all of the smallest parts that make an icicle, we can see them holding tightly together because they are not very warm.  When they get warmer, they will start to move around each other.  When they get very hot, they will become so excited they will bounce off each other and into the air as a gas.  A physical change is kind of like the difference between sleeping, walking around, and have a CRAZY DANCE PARTY.


Let's start with the sleeping part.  When our smallest building blocks are cold, they get really close to each other.  This will keep them from moving around each other, but they will never stop moving all the way.  Freezing is the temperature where the smallest building blocks get so cold that they hold on to each other, making a solid.  This is our icicle.  Even though it is made of water, it's hard and sharp.  This is why you should never look up at an icicle hanging from the roof.  You could lose an eye.  In fact, to be safe, let's melt it down.

Don't look up, you'll poke your eye out.


The icicle droops and then melts in the pot.  We will skip over the part where the smallest building blocks walk around each other.  Oh, are you thirsty?  Take a quick drink, then!  Now stop!  We do not want you to burn your tongue.  Watch as the smallest building blocks become excited by the heat and turn into bubbles.  Dance party!  Boiling is the temperature where the smallest building blocks get so hot that they move enough to bounce off each other and fly into the air as a gas.  This is the white steam you see coming from the tea kettle.  The same little pieces that were hard and pointy and could stab you just a few minutes ago are now flying around and can burn your hand!

Water's ready. Where's my tea cup?


Even the smallest building blocks can break apart.  A chemical reaction is what happens when the bonds that hold the smallest building blocks together break apart and change into something different.  These changes are even smaller than water moving together and bouncing apart.  Have you ever heard someone call water H2O?  That's because it's made of two H's and one O, which are two different elements that we mostly find around us as gases.  When those come apart, they turn from water into something new, but they will still act the same when they meet other things.  If you break a few LEGO blocks off a castle, you can use them to build something new.

Looks like someone ran out of blue LEGO to finish the moat.


Water can change in two different ways.  It can make a physical change where its smallest building blocks become hot and excited and start bouncing off each other, like in steam, or cold enough to hold tight to each other, like in an icicle.  They can also make a chemical change, where the building blocks come apart and the water turns into something new.  Just remember, when testing sharp icicles or hot steam, be careful with your eyes and fingers.  Unless you test them both at the same time.  The steam will make an icicle not so sharp, and an icicle will make steam not so hot.



References:

NeoK12.  "Chemical Reactions"  NeoK12, 2010.  <http://www.neok12.com/Chemical-Reactions.htm>

Chem4Kids.  "Chemical vs. Physical Changes"  Chem4Kids, 2009.  <http://www.chem4kids.com/files/matter_chemphys.html>