Unit 2 Matter, Energy, and

Changes

EnergyEnergy is the capacity to do work

or produce heat.

Energy• Forms:

Radiantex. sunlight

EnergyKinetic

energy carried by objects in motion (includes mechanical & thermal)

EnergyPotential

due to position/stored energy (includes electrical & chemical)

What is the Law of Conservation of EnergyLaw 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.

MatterWhat 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

• 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

The Kinetic Theory of GasesMakes 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: Gasno definite shape or volume particles randomly scattered particles moving quickly in constant

motionlow densityhighly compressiblerapid diffusionhigh expansion on heating

States:Liquid no set shape definite volume particles somewhat organized particles free to moveslightly compressible high densityslow diffusionlow 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

VaporizationLiquid changes to a gas, also called

evaporation, requires energy input to break the intermolecular forces

Changes of State

VaporizationLiquid 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

VaporizationLiquid changes to a gas, also called evaporation, requires energy input to break the intermolecular

forcesRapidly moving particle near surface of liquid gains enough energy to

escape attractive forces of other particles

Volatile liquid – one that readily evaporates

Changes of StateIs 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 StateMore 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 StateBoiling• Making bubbles of

gas• Forces liquid level to

rise• Must push against air

pressure on the liquid

Changes of StateBoiling• 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 StateChanging 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

MeltingMelting point - temperature at

which solid and liquid form of substance exist in equilibrium, also called freezing point

Changes of State

SublimationSolid changes directly to a gas,

requires energy input to break the intermolecular forces

Changes of State

DepositionGas changes directly to a solid,

releases energy

Liquid

Solid

Gas

Require energy to break IM forces

Release energy

Sublimation

Deposition

Melting

Vaporization

Freezing Condensati

on

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 diagramsRelates 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

EnergyMeasuring:• 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

EnergyMeasuring:• SI unit is Joule (J), 1 J is about

the energy to lift a medium-sized apple 1 meter from ground1 cal = 4.184 J

EnergyLaw of Conservation of Energy:in any process, energy is neither

created nor destroyed

TemperatureWhat 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

TemperatureUnits for Temperature• Fahrenheit• Celsius• Kelvin (SI units)

TemperatureUnits for Temperature• Kelvin (SI units)

Why don’t we use a degree mark with Kelvin temperatures?

Lowest temperature reading in Kelvins is called Absolute zeroAt this temperature KE is zero.

Movement stops

TemperatureUnits for TemperatureA quick look at the three scales.

0 C = 273 K = 32 F100 C = 373 K = 212 F

TemperatureConverting Fahrenheit/Celsius• C = 5/9 × (F – 32)

Temperature• Convert 98.6 F to C

Temperature• Convert 25 C to F

TemperatureConverting 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).

TemperatureTemperature affects how fast these particles move. The higher the temperature the faster the particles move. Moving particles possess kinetic energy.

TemperatureTemperature is defined at the average kinetic energy of the particles of an object.

Thermal EnergyThermal Energy is the sum total of all of the energy of the particles of an object.

Thermal energyThermal energy and temperaturetemperature are related though DIFFERENT.

TemperatureTemperature is the average kinetic energy of the particles of an object.

Thermal energyThermal 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 heatheat?

HeatHeat is thermal energy that flows from something at a higher temperature to something at a lower temperature.

What is specific heatspecific heat?

Specific heatSpecific heat is a property of matter which determines how readily a material absorbs heat and changes temperature.

Specific HeatSpecific 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 EnergyTransferring Thermal Energy

(YOU MUST KNOW THIS!!!!!)

ConductionConduction – direct contact

ConvectionConvection – through a fluid

RadiationRadiation – by electromagnetic waves

What is heat transfer by conductionconduction?

•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 convectionconvection?•Heat is transferred through a substance through currents. This occurs in fluids (liquids AND gases)•ConvectionConvection 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 radiationradiation?

•RadiationRadiation 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!!!