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0:01You're watching FreeSchool!
0:07No matter where you are, or what you are doing, things are changing all around you.
0:15Whether it's plants growing or logs burning, or even if you're just eating food, the materials
0:23around you are changing in size, shape, and structure; releasing or absorbing energy,
0:31and creating new substances.
0:36In chemistry, most changes are divided into two categories: physical changes, and chemical
0:42changes.
0:45A physical change is something that changes the physical properties of an object or substance
0:50- like size, shape, or form.
0:55Cutting a piece of cloth is an example of a physical change.
0:59Even though the cloth changes shape and size when it is cut, it does not create a new substance.
1:06It's still cloth!
1:09Even if the pieces of cloth are sewn together and made into a shirt, only physical changes
1:14have occurred.
1:16The shirt is still made of the same substance as the original cloth, just in a new form.
1:23Another type of physical change involves changing states of matter, and water is a great example
1:29of this.
1:31Ice melts and becomes water, and water evaporates to become steam, but no matter its form, the
1:38water is still water.
1:41One way we can tell this is a physical change is that the change can be undone.
1:46Water vapor can condense back into liquid water, and liquid water can be frozen back
1:51into ice without changing to a different substance.
1:57In fact, many physical changes can be undone.
2:01For example, we know that dissolving sugar into water is a physical change because even
2:07though the sugar and the water are mixed together, they do not combine and create a new substance.
2:13They are still just sugar and water, and they can be separated from each other.
2:20Not all mixtures are as simple to separate as sugar and water.
2:24When you mix butter, sugar, flour, and eggs, there is not a practical way to separate them
2:31again, but it is still only a physical change.
2:35The chemical change occurs when you put your mixture in the oven and add heat.
2:42Baking has many of the indications of a chemical change.
2:47The mixture in the oven absorbs heat.
2:50It also changes color and produces an odor.
2:54Gases are released, which is what helps the baked goods to rise.
2:59Finally, this change cannot be undone - you can't unbake a cake.
3:06Chemical changes occur when the particles of two or more substances are rearranged to
3:11form a new substance.
3:14For example, when you burn wood, the wood is transformed into a new substance - ash.
3:23Just like in baking, this change cannot be undone.
3:28Also like the cookies, the wood changes color, releases gases - smoke - and produces an odor.
3:38Unlike in baking, this chemical change releases heat and gives off light.
3:45Chemical changes take place all around us.
3:49Metal rusting, fireworks exploding, fruit ripening, and digesting food are all examples
4:04of chemical changes!
4:06Here are some clues to look at if you're not sure whether something is a chemical or physical
4:11change.
4:13Chemical changes always form a new substance.
4:17They may absorb or release heat.
4:21Sometimes a chemical change will cause a change in color, produce an odor, create a sound,
4:28release gases, or produce light.
4:32Chemical changes usually cannot be undone.
4:37Physical changes do not form a new substance.
4:41A physical change may change the shape or size of an object.
4:46It may change the state of a substance's matter.
4:50Many physical changes can be undone in some way.
4:54In a physical change, you end up with the same substance you started with, even if it
4:59looks different.
5:03I hope you enjoyed learning about physical and chemical changes today.
5:08Look around and see if you can identify the physical and chemical changes around you!
5:14Goodbye till next time!