Thermal Energy

1
Thermal Energy
2
Thermodynamics

• Thermodynamics is the study of heat
  transformations into other forms of energy.
• Thermodynamics is closely linked to the Kinetic
  Molecular Theory.
• The Kinetic Molecular Theory states that all
  matter is made up of tiny particles (atoms) in
  constant, random motion.

3
Because the particles making up matter are
constantly moving, they possess ___ energy.

• electrical
• kinetic
• nuclear
• potential

4
Thermal Energy

• Thermal energy is the overall energy of motion of
  the particles that make up the object.
• In a hot object, the average energy of the
  particles is higher than that of the cold
  object.
• Temperature is a measure of the average kinetic
  energy of the particles in the object.
• The greater the average kinetic energy, the
  higher the temperature.
• Temperature does not depend on the number of
  particles in a sample.

5
Consider two blocks of steel. One block has a
mass of 1 kg and the second has a mass of 2 kg.
Which of the following is true if both blocks are
at the same temperature?

• The particles in the 1 kg block have a greater
  average kinetic energy.
• The particles in the 2 kg block have a greater
  average kinetic energy.
• The particles in both blocks have the same
  average kinetic energy.
• Both blocks have the same thermal energy.

6
Consider a glass of boiling water and a bucket of
boiling water. Which of the following is not
true?

• Both containers have the same temperature.
• The particles in both containers have the same
  average kinetic energy.
• Both containers have the same thermal energy.

7
The kinetic energy of an object or particle
depends on velocity and ____.

• mass of the object.
• volume of the object.
• density of the object.
• color of the object.

8
Air is mixture of various gases including
nitrogen, oxygen, and carbon dioxide. Nitrogen
molecules are the lightest in mass and carbon
dioxide molecules are the most massive. Which of
the following is true?

• All of the molecules have the same kinetic
  energy.
• All of the molecules are moving at the same
  velocity.
• Nitrogen molecules are moving the fastest.
• Both a and c

9
Measuring Temperature

• Temperature is measured with a thermometer.
• The microscopic process involves collisions and
  energy transfers between the thermometer and the
  material whose temperature is being measured.
• Thermal energy is transferred from a hot object
  (greater kinetic energy) to a cold object (less
  kinetic energy).
• Energy is transferred through the process of
  conduction.
• Conduction is the transfer of kinetic energy due
  to the collisions between particles.

10
Conductors vs. Insulators

• Some materials are better conductors than others.
• Metals are good conductors of thermal energy.
• Plastic, styrofoam, and wood are all poor
  conductors of heat.

11
Temperature Scales

• Fahrenheit scale-used when measuring weather
• Celsius scale-used with the metric system
• oF 9/5oC 32 or oC 5/9(oF -32)
• Kelvin scale-based on absolute zero (the lowest
  possible temperature particles have stopped
  moving) -273oC or -459oF
• oC 273 K

12
50oC ___ K

• -223
• 50
• 150
• 323

13
100 K ___oC

• -173
• 100
• 73
• 373

14
Methods of Heat Transfer

• Conduction-transfer of heat through direct
  contact between the particles.
• Convection-transfer of heat through the motion of
  fluid (either liquid or gas).
• Radiation-transfer of heat by electromagnetic
  waves (presence of matter is not necessary).

15
When sitting in front of a fire, you are being
warmed by the process of

• conduction
• convection
• radiation
• All of the above

16
A microwave oven heats food through the process
of

• conduction
• convection
• radiation
• All of the above

17
A metal rod held in a flame eventually becomes
warm through the process of

• conduction
• convection
• radiation
• All of the above

18
Weather patterns are the result of heat transfer
by

• conduction
• convection
• radiation
• All of the above

19
Thermometers measure temperature through the
process of

• conduction
• convection
• radiation
• All of the above

20
The upstairs of a two story house is often warmer
than the first floor due to heat transfer by

• conduction
• convection
• radiation
• All of the above

21
Your home is insulated to prevent heat loss by

• conduction
• convection
• radiation
• All of the above

22
Measuring Heat

• Heat is measured with a calorimeter.
• The unit used when measuring heat is the calorie
  (cal) or joule (J).
• A calorie is the amount of heat needed to raise
  the temperature of 1 gram of pure water 1oC.
• 1 calorie 4.18 joules.
• 1000 calories (1 kcal) 1 dietary calorie (Cal)

23
At a birthday party, a guest eats 500 Cal of ice
cream and cake. To compensate, the guest wants
to do an equivalent amount of work climbing
stairs. How much total height must the person
walk? Assume the persons mass is 60 kg.

• 3.6 m
• 36 m
• 360 m
• 3600 m

24
Heat Capacity

• Specific heat capacity is the amount of heat it
  takes to raise the temperature of 1g of a
  substance 1oC.
• The heat capacity depends on the mass and the
  chemical make-up of the substance.
• Water has a high specific heat capacity compared
  to other substances-therefore, it requires more
  heat to change the temperature of a sample of
  water.

25
Calculating Heat and Specific Heat

• The equation for calculating heat
• heat mass x change in temp x specific heat
• or
• q m x ?T x C
• Mass (m) is measured in grams
• ?T final temp initial temp (oC)
• C is the specific heat
• when working with water, C 1.00 cal/goC or
  4.18 J/goC.

26
How much heat is needed to raise the temperature
of 50.0 g of water from 4.5oC to 83.0oC?

• 3930 J
• 16,400 J
• 940 J
• 17,300 J

27
Changes in States of Matter

• Gain in energy
• -melting-solid to liquid
• -vaporization-liquid to gas (this includes both
  evaporation and boiling)
• -sublimation-solid to gas
• Loss in energy
• -freezing-liquid to solid
• -condensation-gas to liquid
• -deposition-gas to solid

28
Energy Changes in States of Matter

• The energy required to melt 1 kg of a substances
  is called the heat of fusion of that substance.
• The heat required to melt a solid is equal to the
  mass of the solid times the heat of fusion of the
  solid. Q mHf
• The energy required to vaporize 1 kg of a liquid
  is called the heat of vaporization.
• The heat required to vaporize a liquid is equal
  to the mass of the liquid times the heat of
  vaporization of the liquid. Q mHv

29
Suppose that you are camping in the mountains.
You need to melt 1.50 kg of snow at 0.0oC and
heat it to 70.0oC to make hot cocoa. How much
heat will be needed?

• 501 kJ
• 439 kJ
• 940 kJ
• 3830 kJ