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Unit 2
Matter, Energy, and
Changes
Energy
Energy is the capacity to do work
or produce heat.
Energy
• Forms:
Radiant
ex. sunlight
Energy
Kinetic
energy carried by objects in
motion (includes mechanical &
thermal)
Energy
Potential
due to position/stored energy
(includes electrical &
chemical)
What is the Law of Conservation of Energy?
Energy cannot be created nor destroyed….but….
Energy can be transformed from one type to another.
In this diagram, electrical
energy is converted into
thermal (heat) energy and
light energy.
There are many energy transformations in an
automobile.
The explosion of the gasoline involves the release of
chemical energy.
The chemical energy causes the pistons in the
engine to move (mechanical energy)
The moving pistons affect many moving parts
including a generator which produces electrical
energy which keeps the battery charged.
The moving pistons and other moving parts also
produce heat energy.
Objects can convert potential energy to kinetic energy
or kinetic energy to potential energy.
The diagram below illustrates this relationship.
Matter
What holds one molecule or atom
to another?
Intermolecular Forces (forces
between neighboring particles)
Intermolecular Forces
• There are different kinds of
intermolecular forces.
• Some are very weak and break easily.
• But many of them together make a strong
network.
Physical State of Matter
State of matter at room temperature
depends on strength of
intermolecular (IM) forces
• For example, a substance with strong
IM forces will be a solid while a
substance with very weak IM forces
will be a gas
• To understand why intermolecular forces
are important, we must first talk about
molecule movement and kinetic energy
• The Kinetic Molecular theory helps
explain why a solid has certain behaviors
that are different than gases or liquids.
Kinetic Theory and states of Matter
• Kinetic theory says that molecules are
in constant motion.
• Perfume molecules moving across the
room are evidence of this
The Kinetic Theory of Gases
• Kinetic Theory helps to explain why a gas
behaves as it does.
• It also helps us understand the changes in
physical states of matter
The Kinetic Theory of Gases
Makes three descriptions of gas particles
1. A gas is composed of particles, molecules,
•
•
or atoms
Considered to be hard spheres far enough
apart that we can ignore their volume.
Between the molecules is empty space.
2. The particles are in constant random
motion.
• Move in straight lines until they bounce
off each other or the walls.
3. All collisions are perfectly elastic
• The molecules don’t travel very far
without hitting each other so they move
in random directions.
States: Gas
no definite shape or volume
particles randomly scattered
particles moving quickly in constant
motion
low density
highly compressible
rapid diffusion
high expansion on heating
States:Liquid
 no set shape
 definite volume
 particles somewhat organized
 particles free to move
slightly compressible
 high density
slow diffusion
low expansion on heating
Properties of Liquids
Viscosity – friction or resistance to
motion, increases as temperature
decreases
Surface tension – molecules at the
surface experience imbalanced
attractive forces
• Both gasses and liquids are fluids.
–This is because of weak intermolecular
forces.
–The molecules can slide easily over
each other.
States:Solid
• has particular shape
• definite volume
• particles very organized and close
together
• particles move only very slightly
• low compressibility
• high density
• slow diffusion
• low expansion on heating
• Intermolecular forces are strong
• Molecules move - can only vibrate and revolve
in place (they cannot flow past each other)
• Melting point, MP, is the temperature where a
solid turns into a liquid (MP is the same as the
freezing point)
• When heated, the particles vibrate more rapidly
until they shake themselves free of each other.
• As they are heated the temperature doesn’t
change.
– The energy goes into breaking bonds, not
increasing motion.
– Move differently, not faster.
Basic Types of Solids
Crystalline solids –
Amorphous solids -
Crystalline Solids
• are made of atoms arranged in highly ordered,
patterns called unit cells (regular repeating
three dimensional arrangement of atoms in a
solid)
• Most solids are crystals
• Break at certain angles
– Examples: table salt, table sugar, emeralds
Amorphous solids
• appear solid, but are more of a super-cooled
liquid, have high viscosity, gradually soften as
temperature increases
• Rigid but lacking orderly internal structure
• Do not melt - just gradually get softer as
temperature increases
• Shatter at random angles
• Examples: glass and plastics
Properties of Solids
Some solids are good conductors
due to particles being in contact
with each other and passing the
energy from one to another
Matter & Changes
Changes of State
Energy and change of state…
To change states, particles must
overcome the attractive forces
holding them together (the
number of particles does not
change)
Changes of State
Vaporization
Liquid changes to a gas, also called
evaporation, requires energy
input to break the intermolecular
forces
Changes of State
Vaporization
Liquid changes to a gas, also called evaporation, requires energy input to break
the intermolecular forces
Rapidly moving particle near
surface of liquid gains enough
energy to escape attractive
forces of other particles
Changes of State
Vaporization
Liquid changes to a gas, also called evaporation, requires energy input to break the intermolecular
forces
Rapidly moving particle near surface of liquid gains enough energy to
escape attractive forces of other particles
Volatile liquid – one that readily
evaporates
Changes of State
Is vaporization the same as evaporation?
• Not quite…
– Vaporization - the change from a liquid to
a gas below its boiling point
– Evaporation - vaporization of an
uncontained liquid (no lid on the bottle)
Changes of State
More on Evaporation…
• Molecules at the surface break away and
become gas
• Only those with enough KE escape
• Evaporation is a cooling process.
• It requires energy
Changes of State
Boiling
• Making bubbles of
gas
• Forces liquid level to
rise
• Must push against air
pressure on the liquid
Changes of State
Boiling
• A liquid boils when the vapor pressure = the
external pressure (temperature is called the
boiling point)
• Normal Boiling point is the temperature a
substance boils at 1 atm pressure.
– The normal boiling point of water is 100o C
• The temperature of a liquid can never rise
above it’s boiling point
• Energy goes into breaking forces, not moving
faster
Changes of State
Changing the Boiling Point…
• Lower the pressure (like going up into the
mountains)
– Lower external pressure requires lower
vapor pressure
– Easier to make bubbles
– Lower vapor pressure means lower boiling
point.
– Food cooks slower
Changes of State
Changing the Boiling Point…
• Raise the external pressure (like using a
pressure cooker)
– Raises the vapor pressure needed
– Harder to make bubbles
– Raises the boiling point
– Food cooks faster
Changes of State
Boiling point differences…
Different substances boil at different
temperatures because they have
• Different intermolecular forces
– Weak forces → lower boiling point
• Different vapor pressures
– Low vapor pressure → high boiling point
Changes of State
Condensation
• Change from gas to liquid
• Molecules stick together
• Releases energy
Changes of State
Freezing (Solidification)
Particles get closer together and
more organized than in the liquid
state, releases energy
Changes of State
Melting (Liquification)
Particles become less organized
and farther apart, requires energy
input to break the intermolecular
forces
Changes of State
Melting
Melting point - temperature at
which solid and liquid form of
substance exist in equilibrium,
also called freezing point
Changes of State
Sublimation
Solid changes directly to a gas,
requires energy input to break
the intermolecular forces
Changes of State
Deposition
Gas changes directly to a solid,
releases energy
Require energy to break IM forces
Sublimation
Melting
Solid
Vaporization
Gas
Liquid
Freezing
Condensation
Deposition
Release energy
Changes of State
Heating curves
• Describe changes of state of
matter, plot of sample
temperature as a function of time
Changes of State
Changes of State
Phase diagrams
Relates states of matter to
temperature and pressure
Changes of State
Changes of State
Temperature and Phase Change
• The temperature doesn’t change during a phase
change.
• If you have a mixture of ice and water, the
temperature is 0ºC
• At 1 atm, boiling water is 100ºC
• You can’t get the temperature higher until it
finishes boiling
Energy
Measuring:
• calories (cal) – amount of heat
needed to raise temperature of 1 g
H2O by 1 C
1 cal = 1 g × 1 C
•Food energy is in Calories, 1 Cal
= 1 kcal
Energy
Measuring:
• SI unit is Joule (J), 1 J is about the
energy to lift a medium-sized
apple 1 meter from ground
1 cal = 4.184 J
Energy
Law of Conservation of Energy:
in any process, energy is neither
created nor destroyed
Temperature
What is temperature?
• comparison of how hot or cold an
object is with some standard
• measure of the average kinetic
energy of the particles in a sample of
matter.
• The higher the average KE of the
molecules the faster the molecules
are moving => Higher temperature
Temperature
Units for Temperature
• Fahrenheit
• Celsius
• Kelvin (SI units)
Temperature
Units for Temperature
• Kelvin (SI units)
Why don’t we use a degree mark
with Kelvin temperatures?
Lowest temperature reading in
Kelvins is called Absolute zero
At this temperature KE is zero.
Movement stops
Temperature
Units for Temperature
A quick look at the three scales.
0 C = 273 K = 32 F
100 C = 373 K = 212 F
Temperature
Converting Fahrenheit/Celsius
• C = 5/9 × (F – 32)
Temperature
• Convert 98.6 F to C
Temperature
• Convert 25 C to F
Temperature
Converting Kelvin/Celsius
• C = K – 273
Temperature
• Convert 399 K to C
Temperature
• Convert 25 C to K
What is Thermal
Energy?
Particles of matter are in constant motion. This
motion relates directly to the state of matter of the
object (solids, liquids, or gases).
Temperature affects how fast these particles move.
The higher the temperature the faster the particles
move. Moving particles possess kinetic energy.
Temperature is defined at the average kinetic energy
of the particles of an object.
Thermal Energy is the sum total of all of the energy of
the particles of an object.
Thermal energy and temperature are related though
DIFFERENT.
Temperature is the average kinetic energy of the
particles of an object.
Thermal energy is the total amount of energy of the
particles of an object.
A bathtub full of water at 100oF has more thermal
energy than a thimble of water at 100oF. The
temperature is the same but the total amount of
energy is different. The bathtub has more energy.
What is heat?
Heat is thermal energy that flows from something at
a higher temperature to something at a lower
temperature.
What is specific heat?
Specific heat is a property of matter which
determines how readily a material absorbs heat and
changes temperature.
Specific Heat is defined as the amount of heat energy
needed to raise the temperature of 1 kg of a
substance by 1 Co or 1 K.
Notice that water has a very high specific heat,
whereas iron has a low specific heat.
Water requires a lot of heat energy to raise its
temperature.
What is heat?
Heat is thermal energy that flows from something at
a higher temperature to something at a lower
temperature.
What is specific heat?
Specific heat is a property of matter which
determines how readily a material is to absorb heat
and change temperature.
Specific Heat is defined as the amount of heat energy
needed to raise the temperature of 1 kg of a
substance by 1 oC or 1 K.
Transferring Thermal Energy
(YOU MUST KNOW THIS!!!!!)
Conduction – direct contact
Convection – through a fluid
Radiation – by electromagnetic waves
What is heat transfer by conduction?
•Heat transfers as particles of an object increase their
collisions as they are heated. These collisions transfer
the heat energy through the object by colliding with
adjacent particles.
What is heat transfer by convection?
•Heat is transferred through a substance through
currents. This occurs in fluids (liquids AND gases)
•Convection currents are caused by heating of a liquid
or gas, the liquid or gas rises, then cools and falls. This
occurs in the mantle of the earth.
•And in the atmosphere.
•Most of our weather patterns are the result of
convection currents in the atmosphere.
What is heat transfer by radiation?
•Radiation is heat transfer by electromagnetic
waves. These waves may pass through all states of
matter and also through NO matter – such as the
vacuum of space.
•This energy is often called radiant energy.
•Radiant energy from the sun travels through the
vacuum of space until it reaches the earth.
How is heat flow controlled?
Insulators – a material which does not allow heat to
pass through it easily.
Some animals have good
insulation to survive
severe winters.
Buildings and houses are insulated so that heat does
not pass out of them in winter or into them in
summer.
What are some other uses of insulation? Some animals
have good
insulation to
survive severe
winters.
Using heat – How do we use heat in our lives?
Forced-Air Systems – a fuel is burned in a furnace and
a fan circulates the heat in the house
Radiator Systems – closed metal containers that
contain hot water or steam. The thermal heat is
transferred to the air and circulated by convection
currents.
Electric radiators – heat metal coils which transfer the
thermal heat to the surrounding air.
Refrigerators, air conditioners, and heat pumps – how
do they work?
A coolant is circulated through pipes by a compressor.
When the pipes get small and narrow the coolant
compresses and changes to a liquid giving off heat
energy. When the pipes get larger, the coolant
changes from a liquid to a gas (evaporates) causing
the area to absorb heat and get cooler
The human coolant – built-in cooling system
The human body has a cooling system which
functions automatically – perspiration/sweat.
Like a refrigeration system,
the evaporation of the
sweat from the surface of
the body causes energy to
be absorbed from the skin,
causing the skin to feel
cooler.
No sweat!!!