Chapter 6: Thermal Energy
LEARNING GOALS
 Define temperature.
 Explain how thermal energy
depends on temperature.
 Explain how thermal energy and
heat are related.
 Calculate the change in thermal
energy.
WARM-UP:
 Name at least 3 ways you can warm
yourself on a cold day. What is the
source of heat for each?
MATTER IN MOTION
 Matter is made up of tiny particles
(atoms and molecules) that are in
constant, random motion.
MATTER IN MOTION
 Since particles are always moving,
they have kinetic energy.
 The faster they move, the more
kinetic energy those particles have.
 http://youtu.be/6VdMp46ZIL8
TEMPERATURE
 Temperature: measure of the
average kinetic energy of the
particles in an object.
 SI Units
 Kelvin (K)
 More common  Celsius (°C)
 1 K is equal in size to 1 °C degree
TEMPERATURE SCALES
Water freezes at:
 32°F
 0°C
 273 K
TEMPERATURE SCALES
Water boils at:
 212°F
 100°C
 373 K
TEMPERATURE SCALES
 Converting from Fahrenheit to Celsius
 °C = 5 / 9 (°F - 32)
 Converting from Celsius to Fahrenheit
 °F = 9 / 5 (°C )+ 32
TEMPERATURE SCALES
 Converting from Celsius to Kelvin
 K = °C + 273
 Converting from Kelvin to Celsius
 °C = K - 273
PRACTICE PROBLEMS
 Convert 46 °F to Celsius
PRACTICE PROBLEMS
 Convert 37 °C to °F
PRACTICE PROBLEMS
 Convert 25 °C to Kelvin
THERMAL ENERGY AND
HEAT
 Thermal energy: the sum of the
kinetic and potential energy of all
the atoms in an object
 Increases as temperature increases
 At constant temperature, thermal
energy increases if mass increases
THERMAL ENERGY AND
HEAT
 Which will cause the greatest
increase of temperature of a
children’s swimming pool that is at
50°F?
 A cup of water at 100°F
 A large barrel of water at 80°F
THERMAL ENERGY AND
HEAT
 Heat: thermal energy that flows
from something at a higher
temperature to something at a
lower temperature
 Heat is a form of energy, so it can be
measured in joules or calories
THOUGHT QUESTION:
 Your car is parked for several hours
outside on a hot, sunny summer
day. You open the door to the car
and sit down in the seat. What are
you careful not to touch? What
aren’t you afraid to touch? Why?
MEASURING HEAT
 Heat cannot be measured directly.
 However, an increase in temperature
indicates that heat is being added.
 A decrease in temperature indicates
that heat is being removed.
MEASURING HEAT
 Heat will be measured in calories
(cal).
 calorie: the amount of heat energy
needed to raise the temperature of 1
gram of water by 1°C.
 1 calorie = 4.184 J
MEASURING HEAT
 The amount of heat needed for a
given temperature change depends
on the mass.
 It takes 1 calorie of heat to change 1
gram of water by 1°C. It would take
10 calories of heat to change 10
grams of water 1°C.
SPECIFIC HEAT
 Specific heat: the amount of heat
energy that is needed to raise the
temperature of 1 gram of a
substance by 1°C
 Example: The specific heat of water
is 1 calorie per gram per degree
Celsius. (1.00 cal/g°C)
SPECIFIC HEAT
 Heat gained or lost = Mass x Change in
Temperature x Specific Heat
 q = m x ΔT x C




q = heat in calories
m = mass in g
ΔT = change of temperature in °C
C = Specific heat in cal/g°C
SPECIFIC HEAT
 m = (ΔT x C) / q
 C = (m x ΔT) / q
 ΔT = (m x C) / q
 ΔT = Final temp – Initial temp
EXAMPLE
 How much heat is needed to raise the
temperature of 4 grams of aluminum
by 5 °C?
 (The specific heat of aluminum is 0.22
cal/g ° C)
CALORIMETRY
 Calorimeter: an instrument used to
measure the heat given off by a
chemical reaction
 Works because within a closed
container, the heat lost by one
substance must equal the heat
gained by another substance.
CALORIMETRY
 Heat energy will not change the
temperature of a substance when
the heat energy is stored.
 Examples: food and gasoline
 Heat energy is released when the
substances burn
CHECK-IN:
 Using an arrow, draw the direction
of energy transfer between the two
objects below:
78°C
89°C