Transcript www.lbalberti.it

Changing States
of Matter
PART ONE
What states of matter do you
know?
We are going to analyse just three of them,
the main ones:
Solid
Liquid
Gas
Now, name at least two examples
for each of the three states.
Materials can be changed from one
state to another by adding ...
energy
And what's the easiest energy around?
Probably
heat!
But matter changes if you take away heat from it,
too.
Adding energy is
HEATING
Taking away energy is
COOLING
Heating
Heat can change solids into liquids or
gases.
Most solids melt into liquid when they
are heated.
A liquid evaporates into a gas when
it is heated.
Let's see what happens to water.
If ice (solid) is heated, it changes to water (liquid).
This change is called
melting.
Water (liquid) can change to water vapour (gas).
This is called
evaporation.
If water (liquid) is heated until it boils, it changes
to water vapour (gas) very quickly.
Cooling
Cold can change gases and liquids.
Gases may change to liquids.
This change is called
condensing.
Liquids may change to solids.
This change is called
freezing.
Cooling
If water vapour (gas) is cooled, it changes to water
(liquid). This change is called
condensing.
If water (liquid) is cooled, it changes to ice (solid).
This change is called
freezing.
Different solids melt at different
temperatures, some high, some low. These
are called their...
melting points.
Different liquids freeze at different temperatures.
Scientists use something called a freezing point
to measure when that liquid turns into a solid
Finally, different gases turn to liquids at different
condensation points.
Sublimation:
 This is when a solid, on heating, directly
changes into a gas without melting, AND the
gas on cooling re-forms a solid directly without
condensing to a liquid.
They usually involve just a physical change
BUT its not always that simple!
Chemical vs. Physical Changes
It is important to understand the difference
between chemical and physical changes.
The two types are based on studying chemical
reactions and states of matter.
Physical changes are about
energy and states of matter.
Chemical changes happen on a molecular level.
When you melt an ice cube you have forced a
physical change (adding energy).
That example caused a change in the state of
matter.
You can cause physical changes with forces like
motion,
temperature,
pressure.
Now, we know matter can change from one state
to another.
But what happens inside matter when such
changers occur?
Pressure
Let's start it all over agian...
What is a solid?
Solids are usually hard because their molecules have
been packed together.
The closer your molecules are, the harder you are.
Solids also can hold their own shape.
A rock will always look like a rock unless something
happens to it.
Even when you grind up a solid into a powder, you will
see little tiny pieces of that solid under a microscope.
Liquids will move and fill up any container.
Solids like their shape.
In the same way that a solid holds its shape, the
atoms
inside of a solid are
not allowed to move around too much.
This is one of the physical characteristics of
solids.
Atoms and molecules in liquids and gases are
bouncing and floating around, free to move
where they want.
The molecules in a solid are stuck.
The atoms still spin and the electrons fly around,
but the entire atom will not change position.
The second state of matter we will discuss is a
liquid.
Solids are hard things you can hold. Gases are
floating around you and in bubbles.
What is a liquid? Water is a liquid.
Liquids are an in-between state of matter.
They can be found in between the solid and gas
states.
They do not have to be made up of the same
compounds. If you have a variety of materials in a
liquid, it is called a solution.
One characteristic of a liquid is that it will fill up the
shape of a container.
It fills the bottom first because of gravity.
The top part of a liquid will usually have a flat
surface.
That flat surface is because of gravity too.
A special force keeps liquids together.
Solids are stuck together and you have to force
them apart.
Gases bounce everywhere and they try to spread
themselves out.
Liquids actually want to stick together.
There will always be the occasional evaporation
where extra energy gets a molecule excited and
the molecule leaves the system.
Overall, liquids have cohesive (sticky) forces at
work that hold the molecules together.
A special force keeps liquids together.
Solids are stuck together and you have to force
them apart.
Gases bounce everywhere and they try to spread
themselves out.
Liquids actually want to stick together.
There will always be the occasional evaporation
where extra energy gets a molecule excited and
the molecule leaves the system.
Overall, liquids have cohesive (sticky) forces at
work that hold the molecules together.
PART TWO: AFTER THE SIMULATION
All matter is made up of tiny particles called
atoms.
These particles are always
moving and are attracted to one another. A
material's state of matter is
determined by the movement of the particles.
The more energy they have,
the further apart they want to get from each other.
Solids
A solid is the state of matter that has the least
amount of energy.
It has a definite shape and volume.
The particles of a solid are packed close together.
The particles of a solid are moving, vibrating back
and forth, but they don't have enough energy to
break away from one another.
A liquid is matter that has a definite volume
but no definite shape.
A liquid takes the shape of its container but
keeps the same volume.
The particles in a liquid move more freely
than those in a solid, but do not have
enough energy to move apart from one
another
Gas is matter that does not have a definite shape
or volume.
The particles in a gas are far apart and move
quickly in all directions.
A gas can expand or be compressed much easier
than a liquid and a solid.
Think of a balloon filled with air. What happens if
you squeeze the air into a smaller part of the
balloon?
The gas particles or random groups of atoms, get
closer together.
Most gases are invisible, such as the air you
breathe.
Plasma, the 4th state of matter, only
happens at very high temperatures. Plasma
is a lot like a gas, except for the fact that
electrons get stripped from neutral atoms
of the element.
It does not occur naturally on Earth, but
can be found in neon signs, fluorescent
lights, plasma tv's, and lightening.
Most of the visible universe is in the state
of plasma, such as stars, which are big balls
of gases (hydrogen & helium) at really high
temperatures.
What happens when I add
energy to a solid?
Physical Change
A Physical Change is a change in the way
an object looks, but not in what the object
is made of. Changing of state, such as a
pond freezing in the winter is an example of
a physical change. The appearance of the
pond has changed, but the composition of
the water has not changed, it is still made
of hydrogen and oxygen. Changing shape is
also a physical change. Like crumpling
paper, cutting a banana, or slicing an apple
are all examples. When you cut, tear, grind,
or bend matter, you cause a physical
change.
Dissolving sugar in iced tea is a physical change,
which is often misconceived as a chemical
change. Salt in water is also another example.
When you not sure whether it is physical or
chemical you can always ask yourself did the
substance change composition after the change.
Chemical Change
In a Chemical Change substances are
changed into different substances.
Fireworks are a prime example of a
chemical change. The explosions and colors
are evidence of changes in compostion.
Chemical changes are often hard to spot,
but there are some signs to look when
determining if it is a change in
compostion. The easiest to spot is a color
change. Have you ever seen an apple slice
turn brown? A chemical change occurs
when an apple reacts with oxygen in the
air. This occurs with other fruits as well.
Leaves changing colors in the fall is also a
good example. Energy is another sign of a
chemical change. Many substances must
absorb energy to have a chemcial change.
For example, what do you add to pancake
batter to make it turn into a pancake?
Energy in the form of heat is added. The
energy is absorbed by the pancake batter
as it undergoes a chemcial change and a
solid pancake is the result.
Conservation of Mass
The Law of Conservation of Mass state that
the total mass of matter is the same before
and after physical or chemical changes. So,
matter cannot be created or destroyed.