Un i t 3Topic 5- Change

of States

Heat Capacity v Specific Heat Capacity

Heat Capacity v Specific Heat Capacity• So how fast does an object heat up?

Heat Capacity

Specific Heat Capacity

Definition

- amount of thermal energy that warms or cools the object by 1 degree Celsius

- amount of thermal energy that warms or cools one gram of a material by one degree Celsius

Describes- a particular object - material the object is

made of

Depends On- mass of the object and material the object is made of

- material the object is made of

Changing of States• What does “changing of states” mean?• When something goes from either solid/liquid/gas

to another form solid/liquid/gas• Water is a great example…– It can melt (solid ice can melt to liquid water)– It can freeze (liquid water to solid ice) – It can become a gas (from liquid water to water vapour

- gas - when it is boiled)

Changing of States• What does “changing of states” mean?• When something goes from either solid/liquid/gas

to another form solid/liquid/gas• Water is a great example…– It can melt (solid ice can melt to liquid water)– It can freeze (liquid water to solid ice) – It can become a gas (from liquid water to water vapour

- gas - when it is boiled)

There is a change of state where it breaks the natural progression … hops from solid directly to gasThis is known as sublimation

Change of State• Any pure substance can exist in all 3 states– Often easier said than done but it is doable

• Time for a review!• Find a partner • Write “Thermal Energy” & “Temperature” &

“Energy” on a piece of paper and …• … explain to me the difference between them!

Thermal vs. Temperature Review• Simply put, heat is the flow of thermal energy.

• Temperature represents average thermal energy. Heat goes from objects with high temperature to low temperature, not high thermal energy to low thermal energy. (Like diffusion)

• For example, a massive glacier will have more total thermal energy than a small hot nail (simply because it has more molecules); however, its temperature is lower because it has less average thermal energy. Therefore, energy will be transferred from the nail to the glacier...

• Thermal energy is the total internal energy of the system. i.e. how fast the molecules are vibrating

Evaporation• When you sweat you tend to cool off … why?• Enter Particle Model• Imagine a liquid (we will use water) in a jar …

Top = moving fast (enough to escape)

Middle/Lower = slower moving particle stay in liquid state

Slower moving = lower temperature

That means what is left is cooler …

WHAT?!

Evaporation• When you sweat you tend to cool off … why?• Enter Particle Model• Imagine a liquid (we will use water) in a jar …

Top = moving fast (enough to escape)

Middle/Lower = slower moving particle stay in liquid state

Slower moving = lower temperature

That means what is left is cooler …

This is known as…Evaporative Cooling

Examples of Evaporative Cooling• Joggers feel cold as their clothes dry out after a

rain storm

• Home owners spray water on the roof to cool house in hot some day

• First aid worker puts a cool cloth on your head

Examples of Evaporative Cooling• During a change of state (phase) the total energy

of a substance …– Increases or decreases

• Why?– They don’t change speed they change state

Un i t 3Topic 6-

Transferring Energy

Transferring Energy• You hold your hand beside a light bulb … your

hand warms up – why?

• The light bulb is an energy source – An object or material that can transfer its energy to

other objects

Transferring Energy - Radiation• The sun shines billions of kms away but we feel it• Energy is transferred even though no material has

travelled from the sun to us, solar cells, etc…

• What is this transfer called?• Radiation– Transfer of energy without any movement of matter

• Energy transferred this way is called Radiant Energy or Electromagnetic Radiation (EMR)

Transferring Energy - Radiation• EMRs can travel through all kinds of material and

they have some unique characteristics …– Behave like a wave– Absorbed & Reflected by objects– Travel really fast (300,000 km/s)

• Colours play a role in absorption / reflection of heat radiation (heat waves) – Dark colour absorb – White colours reflect

Transferring Energy - Conduction• Conduction is the transfer of energy when

particles collide – Simply put … direct contact

• To do this we need two different types of materials– Conductors … most metals as they carry a current or

heat well throughout their entire material– Insulator … these are poor conductors such as wood or

glass so they are good at trapping heat/cold and preventing it from escaping

Transferring Energy - Convection• Convection is the movement of particles (typically

in fluids) carrying its thermal energy with it as it moves

• Can create a current … how?– Heat rises, cools off, drops back down, heats back up

and rises again, repeat …

• Warmer solutions/particles are less dense • Cooler solutions/particles are more dense• Dense = amount of matter/particles in a solution

Transferring Energy - Convection

Transferring Energy - Convection

Transferring Energy - Convection

Transferring Energy - Convection

Transferring Energy Systems

Transferring Energy Systems

Transferring Energy - System• Energy Source – The part of the system that

supplies the energy to the system

• Direction of Energy Transfer – Always transferred away from the concentrated source

• Energy Transformation – Not created or destroyed but transferred from place to place

Transferring Energy - System• Waste Energy – Little amount of thermal energy

lost to surroundings not involved

directly in the transfer

• Control System – What controls the energy transfer

Un i t 3Topic 7- Thermal Energy Sources

Thermal Energy• Think back … what is thermal energy?– Correct– Energy generated by the movement or vibration of

particles

• That being said there must be a whole bunch of different sources!– Oh yes … yes there are!

Transferring Energy - System