Heat and temperature - PowerPoint Presentation

Slide1

Heat and temperature

Unit 2Slide2

What is matter

?

-Matter

is what makes up all substances, whether it is a

solid, liquid or gas

.

Molecules

, atoms and sub-atomic particles are all matter. Slide3

What’s

matter made of?

-All

matter is made up of constantly

jiggling atoms or molecules

.

The motion of these particles determines whether a substance is a solid, liquid, or aSlide4

States of Matter

Solid

Liquid

GasSlide5

What

are the properties of each state of matter

?

-Each

state of matter has different properties

.

SolidsHave definite shape.Have definite volume

In

a solid, the

particles are so close

that the forces of attraction confine the material to create the specific shape.

In solids, the

motion of the particles is severely constrained to a small area, in order for the solid to maintain its shape.Slide6

Liquids

Have

definite volume

.

Takes the

shape of the container

In a liquid, the particles are farther apart, but they are still close enough that attractive forces confine the material to the shape of its container.

In

liquids, the

movement

is somewhat

constrained by the volume

of the liquidSlide7

Gases

Has no

definite shape

Has no

definite volume

In

a gas, the separation between particles is very large compared to their size, such that there are no attractive or repulsive forces between the molecules.

In

gases, the

movement

of the particles is

assumed to be random and free.Slide8
Slide9
Slide10

How

does each state of matter

change?

-

Each

change in the state of matter has a specific name.Start from:Change to:NameSolid

liquid

melting

Liquid

solid

freezing

liquidgas

boiling

gas

liquid

condensation

solid

gas

(skipping liquid phase)

sublimation

gas

solid

(skipping liquid phase)

depositionSlide11
Slide12

-

Collisions

of particles transfer energy, in effect creating heat transfer by conduction.

Particles

often collide with each other, when this happens

energy is transferred from the faster (hotter) moving particle

to the slower (cooler) moving particle. This makes the slower moving particles increase in speed.What does this have to do with energy transfer or heat flow? Slide13

When molecules in a substance are made to

move faster, they get warmer

. The warmer an object gets, the more kinetic energy

and

thermal energy it

contains.

Kinetic energy – energy of motionThermal energy

– total energy of the atoms and moleculesSlide14

What does all of this have to do with temperature

?

-Temperature

is the measurement of the

average internal kinetic energy

of the material or object.

When a material reaches the temperature at which a change in state occurs, the temperature will remain the same until all the energy is used to change the state.Slide15

How high can something’s temperature go?

-In

principle, temperature has no upper limit.

However

, there is a limit to how cold something can get, it is

absolute zero

. At this point all particle movement has stopped.Slide16

What is heat? What is cold

?

-Heat

is the movement, or transfer of thermal energy.

-

Cold

is the lack of thermal energy.The direction of thermal energy flow is always from warmer to colder.Ex. Hand touches a hot stove – hand gets burned

Ex. Hand touches ice – ice starts to melt. Slide17

Is all of the heat transferred, or is some destroyed

?

-It

can’t be destroyed; it is transferred without a net loss or net gain

.

The

Law of conservation of energy states that energy can not be created or destroyed, it can only be changed from one form to another.Slide18

We apply the above law to thermal systems to get the

First

law of

thermodynamics

:

-Whenever

heat flows into or out of a system, the gain or of loss thermal energy equals the amount of heat transferred. Slide19

The

Second

law of thermodynamics

restates what we’ve learned about the direction of heat

flow.

-Heat

never spontaneously flows from a cold substance to a hot substance. Slide20

The

Third

law of thermodynamics

deals with absolute zero.

-No

system can reach absolute zero.Slide21

Why do some things stay hot longer than others

?

-Different

substances have different capacities for storing thermal energy.

Each substance has its own specific

heat

capacity.The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 degree.Slide22

Heat Transfer & Change of

Phase

Why

does a silver spoon in left in very hot soup

get

hot

too? -Thermal energy is transferred from the hot end of the spoon through the entire length, it’s called conduction.Slide23

Conduction is the transfer of heat energy by collisions between particles in a substance (especially a solid). Electrons in atoms collide with each other inside the object being heated

.

Good conductors of heat are metals with loose electrons – silver, copper, iron, etc

.

Poor conductors are called

insulators

. These don’t have loose electrons – wool, wood, paper, styrofoam, etc. Slide24

Do liquids and gases transfer heat by conduction?

-Liquids

and gases transfer heat mainly by convection

.

Convection is the transfer of heat by motion of a fluid, or by currents.Slide25

When does heat transfer occur

?

-Heat

Transfer occurs whenever matter changes phases.

When

energy is added and absorbed, the change of phase will move in the following direction:

solid > liquid > gas

When

energy is released, the change of phase will move in the following direction

:

gas

> liquid > solidSlide26

What is evaporation?

-Evaporation

is the process by which a liquid changes to the gaseous phase

.

Evaporation

occurs at the surface of a liquid.

Evaporation is a cooling process.Sublimation occurs when molecules jump from a solid phase directly to a gaseous state.

Ex

. Think of dry ice.Slide27

What’s the opposite of evaporation?

-Condensation

Condensation is the changing of a gas to a liquid

.

Condensation is a warming process.Slide28

How does boiling relate to evaporation

?

-Boiling

is evaporation within a liquid.

Boiling

is a cooling process.Slide29

What is melting

?

-Melting

occurs when a substance changes from a solid to a liquid.

As

the kinetic energy increases, the molecules can not stay in the same tight structure of the solid.Slide30

What’s the opposite of melting?

-Freezing.

Freezing

occurs when a liquid changes to a solid.Slide31

What do you need for a change of phase

?

-Energy

A

transfer of energy occurs at every change of phase.

Heat

of Fusion – the amount of energy needed to change any substance from solid to liquid (or a liquid to solid).Heat of Vaporization – the amount of energy required to change any substance from liquid to gas (or a gas to liquid). Slide32