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Unit 1 – Physical Properties of Matter

What you need to know for this unit:

ü Describe the properties of gases, liquids, solids, and plasma.

o Include: density, compressibility, diffusion

ü Use the Kinetic Molecular Theory to explain properties of gases.

o Include: random motion, intermolecular forces, elastic collisions, average kinetic energy,

temperature

ü Explain the properties of liquids and solids using the Kinetic Molecular Theory.

ü Explain the process of melting, solidification, sublimation, and deposition in terms of the Kinetic

Molecular Theory.

o Include: freezing point, exothermic, endothermic

ü Use the Kinetic Molecular Theory to explain the processes of evaporation and condensation.

o Include: intermolecular forces, random motion, volatility, dynamic equilibrium

ü Operationally define vapour pressure in terms of observable and measurable properties.

ü Operationally define normal boiling point temperature in terms of vapour pressure.

ü Interpolate and extrapolate the vapour pressure and boiling temperature of various substances from

pressure versus temperature graphs.

Overall this unit is about the 4 states of matter and the properties associated with each state of matter.

You must be able to describe each state and the process in how they change states in a chemistry

sense (energy, movement of energy and molecules etc…). The KMT (Kinetic Molecular Model) is

simply used to explain IF we were to see the movement of the molecules, what would it look like? It is

mainly used for gases since gases behave a lot differently that both liquids and solids. In addition to

explaining the various state changes, vapour pressure must be operationally defined (properly

defined with chemistry words) and used in vaporization and boiling. Once you have understood the

conceptual meaning of the state changes, then you are able to use data to quantify (make into numbers)

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Atomic theory and the four states of matter

To understand the four states of matter, we must first revisit the atomic theory. The atomic theory is that all

things are made up of atoms. When we zoom in and see the individual atoms (this is really not possible), we

should be able to see these “particles” that are the atoms or molecules. These atoms or molecules in a

simpler sense will be represented by circles or 3D balls to show their movement in various states.

The four states of matter

We are familiar with the 3 states of matter since we encounter the 3 everyday. The last state that is

beyond the 3 states of matter is plasma. All 4 states of matter have their very unique properties. In order to

fully grasp the understanding of the 3 primary states of matter, try to envision the molecules when they are in

the various states. Are the molecules packed together? Fluid? What about the energy of the molecules? Are

they fast? Random? What about the spaces between the molecules? Are there any spaces? Or are there a lot

of spaces. Answering the above questions will help you understand the 3 primary states of matter on the

shape, volume, density, energy, and compressibility. The last state, plasma, is a lot different than the 3 states,

so plasma is simply defined as very high energy charged particles, or ions. Plasma is when the atoms have so

much energy that it carries a charge. It is found from radiating away from the sun’s surface (solar winds).

Solids:

Picture an eraser, and try to “pour” the eraser into a beaker. Does the eraser take the shape of

the container? No. Since it does not take the shape of the container, it has a definite shape. What about the

volume? Does the volume change from before entering the beaker to after? No. So it has a definite volume.

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What about if you were to visualize the particles inside the eraser, are they all spaced out? No, as a matter of

fact, they are actually so compact that they can’t move. So if the molecules don’t have much room to move,

then it must be very dense! The density of solids is a lot denser than liquids and especially gases (with the

exception of water). Water is an exception because frozen water or ice is actually less dense than liquid water.

This is due to the crystal structure of the solid water form compared to the liquid form. The solid crystal form of

frozen water actually provides more room between the molecules than in liquid form. Imagine if solid water

were to be denser than liquid water, would we still have polar bears? Also, since all particles have energy (as

long as it is above absolute zero of -273C or 0K), they must move, but because there is hardly any room for

the molecules to move, they vibrate. Therefore, in all solids, the molecules, instead of bouncing back and forth

on the container, the molecules are vibrating on the same spot.

Solid structure: Particle view

Summary of a solid:

¤ Has definite shape and volume

¤ High density and not very compressible

¤ Does not depend on the shape of the container (doesn’t fill it in)

Two main categories of solids: Crystalline and amorphous

In crystalline solids, a crystal structure forms the basic structure of the solid. A crystal structure is an ordered

structure where there is a pattern and symmetry in how atoms are arranged. In an ionic solid, it is a

combination of an anion and cation. They are attracted to each other by electrostatic force of attraction that

keeps them into together. Ionic solids have a higher melting point because of their stronger intermolecular

forces.

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In an amorphous solid, there is a haphazard arrangement of atoms where the symmetry and the 3D

arrangement are lacking. Example of an amorphous solid is glass.

Liquid

Take a beaker of water and pour it into another. Does it take the shape of the container?

Does the volume change before your poured your liquid compared to after you pour it in? In other words, does

your liquid water take up more or less space after your pour it into the beaker? No, because the volume of

water or liquids is constant or definite. But because liquids as you have observed in your water, is a lot more

fluid than solids, the spaces between the particles are a lot more spaced out. Thus, it is less dense than solids

(exception being water). The spaces between the molecules, although larger than solids, are still insignificant

enough to make compression possible. Thus, it is almost incompressible for liquids. Liquids also take up the

shape of the container as well as you have demonstrated by pouring the water into the beaker.

Liquid structure: Particle view

Summary of Liquids

¤ Has a fixed volume

¤ Fills in the shape of container

¤ Less dense than solids

¤ Almost incompressible

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Gases are in a category of it’s own since the properties of gases are so much more different than solids and

liquids. First of all, picture a semi-inflated soccer ball. If you were to squeeze the soccer ball, the size of the

soccer ball is decreased, because the gas inside the soccer ball is compressed. The properties of gases are

so unique because the spaces between the particles are much larger than both liquids and solids that it

changes the entire dynamics of gases. Since the spaces are so much greater in gases, the density is a lot less

than solids and liquids. Furthermore, because of the spaces, gases can be compressed. Take a balloon, and

blow into it. What kind of shape does the balloon take? Yes, it takes any shape the gases make. The shape

of the balloon will depend on the gases, if there are a lot of gases, then it will become bigger, if there aren’t a

lot of gases, the balloon will be ‘flat’. Gases will take the shape of a container. What about the volume? Since

the volume is the space the molecules take up, gases’ volume is the volume of the container. The gas

molecules will fill up the volume of the container, thus taking the volume of the container.

Gas

¤ Takes the shape of the container

¤ Takes the volume of container (this means that the gas molecules can be spread out evenly in

the container or compressed in a smaller container. The volume is when the molecules are

evenly distributed.)

¤ Can be compressed

¤ Gases are in the gaseous state at room temperature

¤ Water Steam is VAPOUR since it is liquid at room temperature.

Gas structure: Particle view

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Plasma

Plasma is simply an ionized gas, where the gas is charged with free electrons because of the amount

of energy plasma contains. Neat fact is that the plasma state is actually the most common state that is found in

our universe. Our sun is practically plasma!

¤ Plasma is simply an unstable mixture of positive ions and electrons.

¤ Can exist is at temperatures of over 100 million degrees Celsius.

¤ However, plasmas are the most common form of matter in the universe, comprising 99% of the

visible universe.

¤ Examples are aurora borealis, lightning, stars, and plasma TVs.

Plasma structure: Particle view

Aurora borealis

How?

Solar winds from the sun, which are charged ions, interact with elements in the earth’s atmosphere.

Because of the magnetic poles of the earth, the charged ions are moved according to the magnetic

poles. The colours depend on the type of element that it hits in the atmosphere.

Green – oxygen – up to 150 miles in altitude

Red – oxygen – above 150 miles in altitude

Blue – nitrogen – up to 60 miles in altitude

Purple/violet – nitrogen - above 60 miles in altitude

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http://koreaplasma.net/english/koreap2_1.htm

Summary of the four states:

States Volume Density Compressible Shape

Solid

Liquid

Gas

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Plasma

Kinetic Molecular Theory (KMT Model)

The Kinetic Molecular Theory (KMT) was proposed to explain the observable properties of gases and

also liquids and solids. The theory explains how gases behave at constant temperature or different

temperatures. If gas particles are in a container at constant temperature, they will eventually collide with each

other and also the walls of the containers. The harder the particles collide, the more “pressure” it exerts. If the

temperature of the container increases, the speed of the particles will increase causing harder collisions, and

ultimately increasing the pressure.

Movement of gases:

• Particles in constant, rapid, straight line motion

• They have no attraction to one another

• If temperature stays constant, the collisions between the particles are completely elastic

LOW Temperature Constant Temperature HIGH Temperature

At constant temperature, the initial energy of the particle is the same as the energy after the collision. This is

called an elastic collision

However, if the temperature is increasing, there is energy put into the system, thus, the particles gain more

energy after the collision, causing more pressure.

Contrast to a drop in temperature, the energy is lost after every collision, thus dropping the pressure.

But, if there is a constant temperature, there is an elastic collision. This again, occurs in gases.

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Inelastic vs elastic collisions

Phase changes

In order for a phase change to occur, there must be a change in energy. Heat can be given off by the

compound or taken in depending which phase change it will undergo.

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Endothermic reaction

When heat or energy enters the system (compound). Example of this is when barium hydroxide is

reacted with ammonium thiocyanate. The exterior becomes “cold” because heat is taken away from the outside

to enter the system.

Particle view:

Exothermic reaction

When heat is given off during the reaction. Example is when you mix sulfuric acid with water. The

container / beaker will get warm because heat is given off.

Particle view:

Melting:

Recall, solids are tightly packed, with high density and the particles vibrate in their own position. If energy is

placed into the solid, the particles will gain more energy causing the vibrations to intensify. Once they vibrate

faster, it will break apart the intermolecular attraction between the atoms causing the particles to enter the next

phase.

Summary¤ When energy is added, the particles become more excited and therefore move faster.

¤ As they move faster, they collide more, causing the intermolecular forces to break down and a change

of state results.

¤ The energy being used is called kinetic energy

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¤ As a solid is heated (energy is absorbed), the forces of attraction between the particles of the crystal

are slowly overcome, allowing some particles to move more freely.

Freezing Point

Freezing point is the opposite of melting point where liquid solidifies into a solid. In order for a liquid to change

into a solid, the particles must slow down, thus, energy must be “taken out” or leave the system.

¤ the temperature at which a liquid solidifies into a solid.

¤ the particles begin to slow down and the forces of attraction between the particles, or intermolecular

forces begin to increase and take hold. Energy is lost to the surroundings

Vaporization

Vaporization is when liquid is changed into gas. In order for vaporization and evaporation to occur,

vapour pressure must be understood and defined.

Vapour pressure varies from liquid to liquid and varies with temperature.

Vapour pressure is the pressure the liquid molecules exert to escape to the

gas phase. In a closed container, there is not change in pressure inside the

system. Thus, there is a dynamic equilibrium of liquid molecules entering the

gas phase and gas phase condensing to the liquid phase. This dynamic

equilibrium is the equal number of particles changing phases. We don’t

normally see water suddenly boil or evaporate because our atmosphere has

pressure. Our atmosphere contains air molecules that act as the

atmospheric pressure. Therefore, the higher the atmospheric pressure, the

more difficult for the liquid to vaporize. However, if the atmospheric were to

lower, then there are less air molecules “sitting” on top of the liquid, making it

easier for the liquid to vapourize.

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Summary:

Vaporization: is the endothermic (heat is put into the system or object) process by which a liquid changes to a

gas or vapour

¤ It includes evaporation and boiling.

Evaporation happens below the boiling point while boiling requires temperature (heat)

¤ In order to understand evaporation and vapourization, vapour pressure must be understood.

¤ In liquids, there is a pressure that is exerted from the molecules.

¤ But the molecules (from the liquid) can’t vaporize because there is also air molecules keeping them in

the phase.

¤ In order for evaporation to occur, the molecules in the liquid must overcome the air molecule or air

pressure. Thus, if the air pressure drops, evaporation can occur easier.

¤ In boiling, heat is needed. Heat causes the molecules to move faster, thus exceeding the

intermolecular forces, boils.

Evaporation

¤ Evaporation occurs when some particles on the surface of the liquid have enough energy to overcome

the forces of attraction between the liquid particles.

¤ Evaporation takes the energy from the surroundings, excites molecules and eventually changes into

vapor.

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So explain why it feels cold when your body is wet?

Explain the why it feels cold when alcohol is placed on your hand? Also why it disappears faster than water?

What can you conclude about the vapour pressure of alcohol compared to water?

Condensation

¤ Condensation: is the exothermic process by which a gas or vapour becomes a liquid

¤ Vaporization and Condensation are said to be in a dynamic equilibrium with one another

¤ This means that in a closed system,

the rate of vaporization = rate of condensation

¤ In other words, the particles escaping as gas equal the particles returning as liquid

¤ Therefore, the level of the liquid will not change at constant temperature.

Sublimation: is the endothermic change from a solid to a gas or vapour without passing through the liquid

state

ex: dry ice (solid CO2) and solid iodine

Deposition: is the exothermic change directly from gas to solid skipping the liquid state.

ex: hoarfrost

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Heating and Cooling curves

Heating and cooling curves are a graphical representation of the phase change of a substance. The heating

curve of a substance can be determined by heating a solid slowly until it changes to the gas phase while a

cooling curve of a substance can be determined by condensing a gas until a solid is formed.

The following curve is a heating curve of ice.

What do you notice?

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Why is there a plateau?

¤ In order for a solid to melt, energy is needed to overcome the intermolecular forces of attraction.

¤ The heat that warms the ice is used to overcome these forces of attraction, rather than

increasing temperature.

¤ The temperature does not increase until all solid has disappeared.

What would happen if the temperature remained at the plateau?

¤ There would be a constant change of states from liquid to solid and vice versa.

¤ This is called dynamic equilibrium because there is an equal change.

Cooling curve of water:

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Interesting facts

¤ Since freezing is an exothermic process (releases heat), farmers in Florida have taken advantage of

this cool science to help with their crops.

¤ When Florida is hit with the occasional cold spell, farmers would spray their crops with water.

WHY?

¤ As the water freezes, heat is released to the plants.

¤ The heat is sufficient to prevent the plants from freezing.

¤ If you watch the news, you may see pictures of orange trees with long icicles hanging from them. It

seems bad, but that's just what the farmers wanted.