Science, Technology, and Society LET REVIEWER
General Education
Lesson 29
Changes in Matter
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| EduReaper |
Look around you
right now. Everything you see is matter, and matter is always changing. The
food you cook, the rain that falls, the rust you see on old metal gates, all of
these are examples of matter changing in some way. But here is something
important that science teaches us: not all changes are the same. Some
changes only affect how something looks, while other changes actually transform
what something is made of at a deeper level.
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| Image from Future Doctors |
Understanding
the difference between these two types of changes is a core concept in science,
and it is also a topic you will encounter in the PRC Licensure Examination for
Teachers. By the end of this lesson, you will be able to look at any change
happening around you and confidently say whether it is physical or chemical,
and you will understand exactly why.
Physical Change
Let us start
with the first type of change. A physical change is a change in matter where
the chemical composition stays exactly the same. This means that even
after the change happens, the substance is still made of the same material it
was before. Nothing new is created. What changes is only the size, shape,
amount, or state of the matter. The substance might look different, but if
you could look at it under a microscope, the tiny particles that make it up
would still be the same kind of particles.
Think of it this
way. If you take a sheet of paper and fold it into the shape of a boat, you now
have a paper boat. It looks very different from a flat sheet of paper, but it
is still paper. The material itself has not changed into something new. That is
the key idea behind a physical change: the identity of the substance is
preserved.
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| Image from Science notes and Projects |
Physical changes
are also generally reversible, meaning you can often bring the material
back to its original form. For example, if you melt an ice cube, you get water.
But if you freeze that water again, you get ice back. The substance went back
and forth without becoming something entirely different.
Example:
You are making a fruit salad. You take a whole mango and cut it into small cubes. You peel a banana and slice it into pieces. You cut a watermelon into bite-sized chunks. After all the cutting and slicing, you now have a bowl full of small fruit pieces. But here is the thing: those mango cubes are still mango, the banana slices are still banana, and the watermelon chunks are still watermelon. The shape and size changed, but the chemical makeup of each fruit is exactly the same as before you touched it. That is a physical change.
A physical change only affects how something looks, such as its size, shape, or state, but the substance itself stays the same. Nothing new is formed.
Changes in the States of Matter
One very
important group of physical changes is the changes in the states of matter.
Remember from the previous lesson that matter can exist as a solid, liquid, or
gas. When matter shifts from one state to another, it is still considered a
physical change because the chemical composition does not change. Water
that freezes into ice is still water. Steam that cools back into water is still
water. The state changed, but the substance is the same.
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| Image from Let's Talk Science |
These state
changes happen because of changes in temperature and energy. When
you add heat or energy to a substance, the particles move faster and the
substance may shift to a higher energy state. When you remove heat, the
particles slow down and the substance may shift to a lower energy state. There
are six specific state changes, and let us go through each one carefully.
Freezing
Freezing
is the process where a liquid changes into a solid. This happens when
heat is removed from a liquid, causing its particles to slow down so much that
they lock into place and form a rigid structure. The temperature at which a
substance freezes is called its freezing point.
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| Image from Expii |
Example:
When you pour water into an ice cube tray and place it inside the freezer, the freezer removes heat from the water. As the water cools down, the particles slow down until they can no longer flow around each other. Eventually, they lock into place and the water becomes solid ice. The water did not become a different substance. It is still H2O. It just changed its state from liquid to solid.
Freezing is when a liquid becomes a solid because heat is removed and the particles stop moving freely.
Melting
Melting
is the process where a solid changes into a liquid. It is the opposite
of freezing. When heat is added to a solid, the particles gain energy and start
to move faster. Eventually, they break free from their fixed positions and
begin to flow around each other, turning the substance into a liquid. The
temperature at which melting happens is called the melting point.
Example:
On a hot summer day, you pull out a chocolate bar from your bag and notice it has already started to soften and bend. If you hold it in your hand for a minute, it starts to melt into a gooey liquid. The heat from your hand and the surrounding air is transferring energy to the chocolate particles, causing them to move faster and break free from their rigid solid structure. The chocolate is still chocolate; it just changed from solid to liquid.
Melting is when a solid becomes a liquid because heat is added and the particles gain enough energy to start moving freely.
Evaporation
Evaporation
is the process where a liquid changes into a gas. When a liquid is
exposed to heat or air, the particles at the surface of the liquid gain enough
energy to escape into the air as gas particles. Evaporation can happen slowly
over time, like a puddle drying up, or it can happen quickly with a lot of heat
applied.
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| Image from Key Stage Wiki |
Example:
After doing the laundry, you hang your wet clothes outside under the sun. After a few hours, the clothes are completely dry. Where did the water go? The water did not disappear. The heat from the sun gave energy to the water particles on the surface of the fabric, and those particles gained enough energy to escape into the air as water vapor, which is water in gas form. The water evaporated. It is still water; it just changed state from liquid to gas.
Evaporation is when a liquid turns into a gas as its particles gain enough energy to escape into the air.
Condensation
Condensation
is the opposite of evaporation. It is the process where a gas changes into a
liquid. When a gas loses energy or comes into contact with a cooler
surface, its particles slow down and come closer together, eventually forming a
liquid. A very common and large-scale example of condensation is how clouds
form in the water cycle. Water vapor rises into the atmosphere, cools down,
and condenses into tiny liquid water droplets that group together to form
clouds. When enough water collects, it falls back to the ground as rain in a
process called precipitation.
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| Image from Expii |
Example:
On a hot day, you pour cold juice into a glass. After a minute or two, you notice that the outside of the glass is covered with tiny water droplets. This is condensation. The water vapor in the warm air around the glass came into contact with the cold surface of the glass, lost energy, slowed down, and turned into liquid water droplets on the outside of the glass. The water did not come from inside the glass. It came from the air around it.
Condensation is when a gas turns into a liquid because it loses energy, often by touching a cooler surface. It is also how clouds form in the sky.
Sublimation
Sublimation
is a unique process where a solid changes directly into a gas, skipping
the liquid state entirely. This happens under specific conditions of
temperature and pressure. Not all solids can sublimate, but some substances do
this naturally.
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| Image from Expii |
Example:
You may have seen dry ice used at parties or in science demonstrations. Dry ice is solid carbon dioxide. When you take it out of its container and leave it at room temperature, you will notice it does not melt into a liquid. Instead, it releases a thick, foggy vapor that sinks to the floor. The solid dry ice is turning directly into carbon dioxide gas without ever becoming liquid first. That is sublimation in action. Mothballs, which are placed in closets to keep insects away, also undergo sublimation over time, slowly turning from solid into gas and releasing their smell into the air.
Sublimation is when a solid skips the liquid stage and turns directly into a gas.
Deposition
Deposition
is the reverse of sublimation. It is the process where a gas changes
directly into a solid, again skipping the liquid stage. This happens when a
gas loses a lot of energy very quickly, causing its particles to lock directly
into a solid structure without first becoming liquid.
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| Image from Expii |
Example:
On a very cold winter morning, you might notice a thin layer of frost covering the grass, car windshields, or windows. This frost did not form by water raining down and then freezing. It formed when water vapor in the cold night air lost so much energy that it turned directly into solid ice crystals on those cold surfaces. The water vapor went from gas to solid with no liquid step in between. That is deposition.
Deposition is when a gas turns directly into a solid by losing energy rapidly, skipping the liquid stage.
Chemical Change
Now we move to
the second and very different type of change. A chemical change is a
change where the chemical composition of a substance is altered. This
means that after the change happens, one or more new substances are
formed that are completely different from the original material. A chemical
change is also called a chemical reaction. The original substances that
go into the reaction are called reactants, and the new substances that
come out are called products.
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| Image from Chemistry Learner |
Unlike physical
changes, chemical changes are generally not reversible. Once a chemical
reaction has taken place, you cannot easily go back to the original substance.
You cannot un-burn a piece of wood. You cannot turn a cooked egg back into a
raw one. The particles have rearranged themselves in a fundamentally new way.
How do you know
a chemical change has happened? There are several signs to look for. These
include: the production of gas (bubbles forming), a change in color,
the release or absorption of heat or light, the formation of a new
solid (called a precipitate) from two liquids, and the production of a
new smell. The presence of one or more of these signs usually tells you
that a chemical change has occurred.
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| Image from Worky Books |
Example:
Think about toasting a slice of bread. You place a fresh, soft, white slice of bread into the toaster. Heat is applied, and within a minute, the bread comes out brown, crispy, and with a slightly different smell. The heat caused a chemical reaction in the sugars and proteins of the bread, creating new substances that were not in the original bread. The change in color to brown and the new smell are both signs that a chemical change has taken place. No matter what you do, you cannot turn that toasted bread back into a soft, white slice. The change is permanent because the chemical composition has been altered.
A chemical change creates one or more brand new substances through a chemical reaction. The original substance is permanently changed and usually cannot be returned to its original form.
Physical Change vs. Chemical Change
Now that you
know both types, let us make sure you can tell them apart. The key question to
ask is: did the substance become something completely new? If the answer
is no and the material is still the same substance just in a different form or
shape, it is a physical change. If the answer is yes and a new substance
has been formed, it is a chemical change.
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| Image from YourDictionary |
Example:
Here are two scenarios side by side. In the first scenario, you crush an aluminum can. The can is now flat and small, but it is still aluminum. That is a physical change. In the second scenario, you leave that same aluminum can outside in the rain for months. Over time, it begins to corrode and change color as it reacts with oxygen and moisture in the air. New substances are forming on the surface. The aluminum is no longer just aluminum in a different shape. A chemical reaction has taken place. That is a chemical change.
If the substance is still the same thing just looking different, it is physical. If it has become a brand new substance, it is chemical. That is the simplest way to tell them apart.
