Internal energy, Temperature & Heat

Salman Al-beshan

Internal energy-the type of motion depends on whether the material is

solid, liquid or gas.

-in the solid the molecules move in fixed position, this is the reason why solid do not change their shape easily.

-in liquids and gases the molecules move randomly, this is the reason why liquids and gases change their shape easily.

2

Solid, liquid and gas

3

Internal energy

-because these molecules are moving, they have kinetic energy, and this molecules also have potential energy because of the force attracting between them.

-so, the total kinetic energy and potential energy of the molecules called internal energy.

4

What is Temperature?• Temperature (T) is a measure of how “hot” or “cold”

something is.

• Temperature is not energy nor is it heat.

• Temperature is a measure of the motion of the atoms/molecules that make-up an object.

– The greater the motion/vibration the greater the T– The smaller the motion/vibration the lower the T

5

Temperature• If the temperature of substance is increased, it

expand.

• If the temperature of substance is decreased, it contract.

• If the temperature of solid is increased, it melts.

• If the temperature of liquid is increased, it boils.

6

Scales of temperature• Temperature is measured in 3 common scales:

1-Celsius or Centigrade (oC)

2-Fahrenheit (oF)

3-Kelvin (K) (SI unit of temperature)

{note: units of Kelvin are not degrees K (or oK), just K}

7

1-Celsius or Centigrade (oC)

-Divides the range between melting point and boiling point into 100 degree(100 oC).

• -The temperature of melting ice is 0 oC.

-The temperature of boiling water is 100 oC.

8

1-Celsius or Centigrade (oC)

9

2-Kelvin (K)

-The temperature of melting ice is 273.15K.

- The temperature of boiling water is 373.15K.

-The significance of this scale is that at 0K the particles which are normally in motion are at rest. That mean at 0K a body has no internal energy.

10

2-Kelvin (K)

-This temperature, which has never been achived,is known as absolute zero.

- absolute zero is the lowest physical achievable temperature.

11

2-Kelvin (K)

12

Comparison between K & oC

13

3-Fahrenheit scale

- Divides the range between melting point and boiling point into 180 degree.

-The temperature of melting ice is 32 oF.

-The temperature of boiling water is 212 oF.

14

Fahrenheit scale

15

Body temperature

16

Temperature scale

Centigrade Kelvin Fahrenheit

Body temperature

37oC 310K 98.4oF

17

Comparison between temperature scales

Latent heat-a solid at a melting point or a liquid at boiling

point can absorb energy without a rise of temperature. for example, liquid which freezes into a solid, can release energy without suffering a fall of temperature.

-This the energy is used to achieve the rearrangement of particles which change the physical state.

18

Latent heat

- This energy is called latent heat.

-For example: to melt 1kg of ice(at 0 oC)into water also(at 0 oC)required about 330kilojoules of energy.

19

Heat Capacity:

-It is the change in internal energy accompanies a one-unit temperature change in the body.

- heat capacity(c)=

internal energy change ÷ temperature change

= J ÷ K

= J K-1

20

Specific Heat Capacity-It is the property of a material or substance rather

than a body or object.

- specific heat capacity = Internal energy change ÷ (temperature change×mass)

= J kg-1 K-1

21

Specific Heat Capacity

– MetalsMetals tend to have tend to have lowlow specific heat capacities specific heat capacities (which is one reason they make great cooking (which is one reason they make great cooking vessels)vessels)

– Non-metalNon-metal substances tend to have substances tend to have higherhigher specific specific heat capacitiesheat capacities

22

Specific Heat Capacity

23

Substance Specific Heat J/g°C

Aluminum 0.895

Calcium 0.656

Carbon (dia) 0.508

Carbon (gra) 0.708

Copper 0.377

Gold 0.129

Iron 0.448

Lead 0.129

Silver 0.712

Water (l) 4.184

Water (s) 2.03

Water (g) 2.02

Specific Heat Capacity

Example.

The anode disc of an X-ray tube is made of molybdenum and has a mass of 0.7kg.during a very rapid angiographic exposure series, estimate the approximate temperature rise if the specific heat capacity is 250 kg-1 K-1 ?

24

Conduction,Convection&Radiation

- There are 3 mechanisms through which energy is transferred by heat,Conduction,Convection and Radiation.

-Conduction is the dominate in solid.

-Convection is the dominate in liquid.

- Radiation is the dominate in vacuum

25

Conduction,Convection&Radiation

26

Conduction-It is the transfer of thermal energy between neighboring

molecules in a substance through direct contact.

-When cooking on the stovetop, the heat from the flame is applied directly to the frying pan. This means that only the flat surface of the pan is sufficiently hot enough to cook anything .

27

Convection-It is movement of molecules within fluid.

-Air or water surrounding a heat source receives heat, becomes less dense and rises. The surrounding, cooler fluid moves to replace it. This cooler fluid is then heated and the process continues, forming a convection current.

28

Radiation-electromagnetic radiation emitted from the surface of an

object which is due to the object's temperature.

- represents the transfer of heat by electromagnetic radiation, The sun is example of radiating objects producing heat.

29

Thank you for your attention

30