Thermal Energy

1
Thermal Energy

• Temperature Thermal Energy
• Change of State Laws of Thermodynamics

2
Thermodynamics

• Study of heat
• Kinetic-molecular theory
• Description of matter as being made up of tiny
  particles in random, constant motion.
• Thermal energy
• The overall energy of motion of the particles
  that make up an object

3
Thermal Energy Temperature

• Temperature
• The hotness of an object as measured using a
  specific scale
• Hotter greater kinetic energy

4
Equilibrium Thermometry

• Conductivity
• The transfer of kinetic energy when particles
  collide
• Thermal equilibrium
• The state where the rate of energy transfer
  between bodies becomes equal the bodies will be
  at the same temperature

5
Equilibrium Thermometry

• Thermometer
• Device that measures temperature

6
Temperature Scales

• Celsius Kelvin
• Absolute zero
• The temperature at which no further thermal
  energy can be removed from an object, -273C

7
Kelvin to Celsius

• 0C 273.15 K

8
Heat Thermal Energy

• Heat (Q)
• Energy that flows between two objects as a result
  of a difference in temperature

9
Thermal energy transfer

• Convection
• Motion of fluid caused by temperature differences
• Radiation
• The transfer of energy by electromagnetic waves

10
Specific heat

• The amount of energy that must be added to the
  material to raise the temperature of a unit mass
  one temperature unit
• C (not C) J/kg K

11
Heat transfer

• Q mC?T mC(Tfinal Tinitial)
• A 0.400 kg block of iron is heated from 295K to
  325K. How much heat had to be transferred to the
  iron?

12
Heat transfer

• Known
• m 0.400 kg
• CA 450 J/kgC
• Ti 295 K
• Tf 325 K

13
Heat transfer

• Q mC(Tf Ti)
• (0.400 kg)(450 J/kgC)(325-295K)
• 5.4 x 103 J

14
Calorimetry Measuring C

• Calorimeter
• A device used to measure changes in thermal
  energy
• Conservation of Energy
• EA EB constant
• ?EA ?EB 0
• ?EA -?EB

15
Change in Thermal Energy

• ?E Q mC?T
• A calorimeter contains 0.50 kg of water at 15C.
  A 0.040 kg block of Zinc at 115C is placed in
  the water. What is the final temperature of the
  system?

16
Change in Thermal Energy

• Zinc Known
• mA 0.040 kg
• CA 388 J/kgC
• TAi 115C

• Water Known
• mB 0.50 kg
• CB 4180 J/kgC
• TBi 15C

17
Change in Thermal Energy

• mACA?T mBCB?T 0
• mACA(Tf TiA) mBCB(Tf TiB) 0
• mACATf mACATiA mBCBTf mBCBTiB 0
• Tf (mACA mBCB) mACATAi mBCBTiB
• Tf mACATAi mBCBTiB / mACA mBCB

18
Change in Thermal Energy

• Tf mACATAi mBCBTiB / mACA mBCB
• (0.04 kg)(388 J/kgC)(115C) (0.50 kg)(4180
  J/kgC)(15C) / (0.04 kg)(388 J/kgC) (0.50
  kg)(4180 J/kgC)
• (1.78 x 103 3.14 x 104)J / (15.5 2.09 x
  103) J/C
• 16 C

19
Change of State

• Solid, liquid, gas
• Melting point
• Temperature at which a solid becomes a liquid
• Boiling point
• Temperature at which a liquid becomes a gas

20
Changes of State

• Heat of fusion
• The amount of heat needed to melt one kilogram of
  a substance
• Heat of vaporization
• The thermal energy needed to vaporize one
  kilogram of a liquid

21
Changes of State

• Heat Required to Melt
• Q mHf
• Heat Required to Vaporize
• Q mHv
• Hf Hv are constant for each material (p. 287)

22
1st Law of Thermodynamics

• The total increase in the thermal energy of a
  system is the sum of the work done on it the
  heat added to it
• Law of conservation of energy

23
Heat engine

• A device able to convert thermal energy into
  mechanical energy continuously
• Autos

24
2nd Law of Thermodynamics

• Natural processes go in a direction that
  maintains or increases the total entropy of the
  universe
• Entropy
• A measurement of disorder in a system