VocabularyMatter: All things are made up of matter. Anything that has mass is matter. I'm matter, You're matter, the computer is matter.
Chemical Change: A change in matter that is irreversible and involves a change on a molecular level. Physical Change: A change in matter that can be reversed, and the molecules in the object have not changed chemically. |
Today's Target: Be able to identify and differentiate between Physical and Chemical changes
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What is a Physical Change?
A physical change includes matter and energy, however, no new substance is created, even if the form looks different. Physical changes are when substances mix, but do not chemically react. In a physical change, the effects of the change are reversible (even if it doesn't resemble the original) One of the popular ways of understanding physical change is how water can be a solid, liquid, and a gas. Neither is a new substance, but each is a different form of matter.
Physical Change Examples
When a pencil breaks, it is still a pencil. While the form of the pencil has changed, the wood, lead, eraser are all still the same on a chemical level, so it is a physical change.
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When the paper is shredded, the paper does take a new form, but like the pencil, the paper is the same on a chemical level. This is a physical change.
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When we boil water, the water becomes steam. This steam is not a chemical change because water naturally has 3 forms solid, liquid, gas. By heating the water, we simply turned it into a different form, but we did not change it chemically. Ice water and steam are all physical changes because there is no chemical change in the water, just a change in form.
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What is a Chemical Change?
A chemical change is a little more complex. While a physical change means nothing changes on a molecular level, chemical changes mean there is a change chemically. These changes are usually irreversible (can't be put back) and change the chemical properties of the object. These result in at least one new substance. They also frequently use light and heat in the chemical changes.
Chemical Change Examples
The friction used in lighting a match is a chemical change. This change is irreversible. We cannot relight the match the same way. The chemical compounds on the match head are used up, and are gone (the red part of the match).
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When cooking an egg, we change the molecular structure. When we cook food, the enzymes in the food actually change. The egg is a chemical change because not only can we not put the egg back as it was before, but its molecular structure (after adding heat) has changed.
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Cake batter is a fun molecular change. While this does not have a change using heat, it has a change using baking soda/baking powder. The powder begins making chemical changes in the batter and begins trapping in air within the batter. This little ingredient does a lot for the cake batter and makes it an excellent candidate for chemical change.
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Cake! Cake is a chemical change because of both baking powder/soda and heat. When you bake a cake, the trapped air from the batter begins to accelerate and rise. Those are the bubbles you see in a cake. Those bubbles are a chemical change, and make our cakes fluffy.
Of course we also cannot reverse a finished cake back into flour, sugar, eggs, and baking powder. Irreversible change. |
Oppositely, apples getting old is also a chemical change. As the apple ages it begins to rot and its molecular structure changes. These changes are irreversible.
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Differentiating between the two
Physical changes are either reversible or no new substances are created.
Chemical changes involve an irreversible change or a new substance created
Chemical changes involve an irreversible change or a new substance created
What's what?
Go down this list and identify whether it is a physical or chemical change
- Shattered Glass
- Burning wood
- Fireworks
- A melting Ice-cream cone
- Your stomach digesting food
- A rusting nail
- Cutting a lemon
- Cracking an egg
- Dissolving sugar in water (What happens if you leave sugar water out)
- Marshmallows over a fire