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A final look at how matter changes states and the role heat energy plays in our world.
Have you ever wondered why your ice cream turns into a sticky soup on a hot day, or where a rain puddle goes after the sun comes out?
Everything you see, touch, or breathe is matter. Matter is made of tiny bits that are always moving! Depending on how those bits move, matter can be in three states. Solids, like a wooden block, keep their shape. Liquids, like milk, flow and take the shape of whatever cup you pour them into. Gases, like the air inside a balloon, spread out to fill up all the space they can find. Even though they look different, they are all made of the same 'stuff'!
Quick Check
If you move a rock from a round bowl to a square box, does its shape change? What state of matter is it?
Answer
No, the shape stays the same because a rock is a solid.
Heat is a form of energy that acts like a 'pusher.' When we add heat to a solid, the tiny bits inside start moving faster and faster until they break loose. This is called melting. If we take heat away (make it cold), the bits slow down and stick together. This is called freezing. For example, water freezes into ice at and melts when it gets warmer than .
Let's see how removing heat changes matter: 1. Pour liquid juice into a plastic mold. 2. Place the mold into a very cold freezer. 3. Wait 4 hours. The freezer removes heat energy from the juice. 4. The liquid juice turns into a solid popsicle!
Quick Check
What happens to the tiny bits in a solid when you add heat?
Answer
They start moving faster and break apart, turning the solid into a liquid.
What happens if we keep adding heat to a liquid? It gets so energetic that it turns into a gas! This is called evaporation. You might see this as steam rising from a hot pot of soup. When gas cools down (loses heat), it can turn back into a liquid. This is why you see tiny water drops on the outside of a cold lemonade glass on a hot day. The gas in the air touched the cold glass and turned back into liquid water!
Imagine a puddle on the sidewalk after a rainstorm: 1. The sun comes out and shines on the liquid water. 2. The sun adds heat energy to the puddle. 3. The water bits move so fast they fly into the air as an invisible gas called water vapor. 4. The puddle 'disappears' because it has changed states!
Think about boiling a pot of water for pasta: 1. You start with 2 liters of liquid water (). 2. You add lots of heat from the stove. 3. You see bubbles and steam (gas) rising. 4. If you leave it too long, you might only have of water left! Where did the other go? It turned into gas and spread throughout the kitchen.
Which state of matter spreads out to fill any container it is in?
What must be added to an ice cube to make it melt?
True or False: Freezing is what happens when you remove heat from a liquid.
Review Tomorrow
In 24 hours, try to remember the three states of matter and one way heat changes them.
Practice Activity
Next time you take a hot bath, look for the 'fog' on the mirror. Can you explain to an adult how that gas turned back into liquid water?