Physical and Chemical Changes

Physical & Chemical

Change

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https://njctl.org/video/?v=nkiMqsTBdTs

Physical and Chemical Change

We learned earlier in the year that:

• All matter is made of atoms.

• Atoms often combine with other atoms in specific ways.

• That single atoms or combinations of atoms are called particles.

There are two types of changes which we will be considering in this
course: physical change and chemical change.

Physical and Chemical Change

Physical change does not change the particles in a
material, just how they are arranged.

Chemical change does change the particles in a material
by creating different particles from the same atoms.

Neither physical nor chemical change alters the atoms
themselves.

Generally, physical changes are considered to be reversible by
physical means.

Sometimes it's said that physical changes are easily reversed...
it isn't always so... but it is possible.

As we discuss some examples, you'll see the sorts of changes
which are considered to be physical changes and you can
decide how easy they would be to reverse.

Physical Change

Changes of State are physical changes.

Changes of state are easy to reverse by just changing the
temperature.

The particles themselves are unchanged by these processes.

For example, water can undergo all these changes and still end
up back at the first stage.

The water particles don't change, just how they are arranged.

• Melting
• Freezing
• Vaporization
• Condensation
• Sublimation
• Deposition

Changes of State

The water is still water.

It just changes state.

And, with the right
conditions, the water can
go back to how it started.

The water particles don't
change regardless of
their state of matter.

Physical Change

For instance, ice can melt, then boil, then condense back to
liquid and then freeze.

https://cdn.pixabay.com/photo/2016/11/12/01/33/glass­1818065__340.jpg

While it wouldn't be easy
to unbreak the glass, it is
possible to melt it back
down and reform it.

So, it's possible.

The particles that
comprise the glass are
unchanged when the
glass is broken.

Physical Change

Breaking glass is a physical change.

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Paper­Shredding­Machine­in­2018­750x400.jpg

The same is true
for sawing wood.

Tearing a cloth.

Crushing a can.

These are all
physical changes.

The particles in the
paper or material
are unchanged.

Physical Change

Cutting or deforming objects is a physical change

Cutting or shredding paper, or any other material, is a physical
change. While difficult to reverse, it is theoretically possible.

https://upload.wikimedia.org/
wikipedia/commons/thumb/8/89/
SaltInWaterSolutionLiquid.jpg/
158px­
SaltInWaterSolutionLiquid.jpg

Dissolving a solid in a liquid is a
physical change.

For instance, dissolving salt or sugar in
water.

By evaporating and collecting the liquid,
the liquid and solid can be separated.

The particles that comprise the liquid or
solid are not changed by the process.

Physical Change

Dissolving a solid is a physical change.

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www.heroninstruments.com/wp­
content/uploads/2017/07/Oil­
and­Water­multi­racial­
churches2.jpg

Mixing oil and water creates a mixture
which can be undone by separating
them again.

The same is true for a mixture of sand
and water; the water can be poured off.

Or, a mixture of salt and pepper; each
piece can be separated again.

Mixing substances together is a
physical change.

The substances don't change, only
their proximity to other substances.

Physical Change

Mixtures represent a physical change.

https://
www.kingarthurflour.com/
sites/default/files/blog­
images/2017/04/Cake­
Mixing­Methods2­4.jpg

Even mixing a number of ingredients to
make a cake is a physical change.

It may be a challenge, but none of the
particles which make up the ingredients
are changed by the mixing process.

So, they could be separated back out
again.

However....

Physical Change

Mixing the batter to make a cake is a physical change

https://letthebakingbegin.com/wp­
content/uploads/2017/09/Simple­
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Begin­2­5­2­500x500.jpg

When you put that cake batter in an
oven and turn on the heat, a
chemical change occurs.

The ingredients react together so
that new particles form from the
atoms that make up the original
particles in the ingredients.

They can't be separated back to their
original form by physical means.

Chemical Change

Baking a cake is a chemical change

Chemical Change

Burning is a chemical change.

The particles in the wood and air
react to form new combinations of
atoms...creating new particles from
the original particles.

Burning is a chemical change

Once wood is burned, it's not possible to
recreate it from the ash and gases which
remain.

New particles have replaced the old
particles, both being combinations of the
same atoms.

Chemical Change

Living things take in air, food,
nutrients, etc. to grow.

The particles that comprise those
inputs to life are broken down and
their atoms used to form new
combinations...new particles that
comprise the living organism.

A physical process cannot recover all
those particles back to their original
form.

Growing animals, plants and trees are chemical changes

Chemistry

To understand chemical change, we will have to look inside
atoms to understand how they are constructed.

Then, we can learn how atoms combine to form different
particles.

And, then can recombine to form new particles during chemical
processes.

Multiple Choice

Reorder the followinga

• a

• a

• a

• a

Multiple Choice

What is the definition of a chemical change?

• Characteristics that describe how a substance behaves under different conditions
• Alteration in the physical state of matter without changing its chemical composition
• Transformation that results in the creation of new substances
• Inherent characteristics that help us identify and describe matter

Multiple Choice

Which of the following is a chemical property?

• odor
• flammability
• boiling point
• conductivity

Multiple Choice

Which of the following is a physical property?

• Ability to react with oxygen
• Ability to rust
• Ability to burn
• Ability to conduct electricity

Multiple Choice

Which of the following is an example of a chemical property?

• Melting point
• Density
• Color
• Ability to react with acid

Multiple Choice

What is the definition of physical changes?

• changes that describe how a substance behaves under different conditions
• characteristics that describe how a substance interacts with other substances
• changes that alter the form or appearance of a substance, but not its chemical composition
• changes that lead to the formation of new substances with different chemical properties

Multiple Choice

What is the definition of a physical change?

• Alteration in the physical state of matter without changing its chemical composition
• Inherent characteristics that help us identify and describe matter
• Characteristics that describe how a substance behaves under different conditions
• Transformation that results in the creation of new substances

Multiple Choice

What type of change occurs when a substance reacts with an acid?

• physical change
• neither physical nor chemical change
• chemical change
• both physical and chemical change

Multiple Choice

What happens to the fundamental particles during a physical change?

• They remain the same
• They break and form new chemical bonds
• They become completely different substances
• They disappear