UNIT 5: HEAT
• What is heat?
• What is temperature?
• How are these related to each other?
KINETIC MOLECULAR THEORY
• All matter consists of tiny particles
• These particles are in constant motion
• The amount of motion is proportional to temperature.
Increased temperature means increased motion
• ex water- solid when below zero, liquid when 0-100
degrees and steam above 100
• Solids, liquids and gases differ in the amount that their
particles move and how much they interact
KINETIC MOLECULAR THEORY
HEAT
• Is the thermal energy transferred from one object to
another due to differences in temperatures. Measured
in Joules (J)
Qheat=
Ethermal
where Qheat = amount of heat;
E= change in thermal energy
TEMPERATURE
• Is a measure of the average kinetic energy of the
molecules of a substance. Can be measured with a
thermometer
• Measurements of a thermometer:
• Celsius (oC)- freezing point is 0oC and boiling point
is 100 oC
• Kelvin Scale (K)- sets absolute zero (temperature
where no motion occurs) as 0 K (-273.15oC).
K= oC +273 or oC= K-273
TEMPERATURE CONVERSIONS
• Convert these temperature from Celsuis to Kelvin
• 27oC = 300 K
• 560 oC = ? K
• -184 oC = ? K
• -273 oC = ? K
• Convert these temperatures from Kelvin to Celsius
• 110K = -163 oC
• 22 K = ? oC
• 402 K= ? oC
• 323 K = ? oC
THERMAL EXPANSION
• When matter is heated, the particles move faster and
move apart from each other. This causes the volume to
increase. We call this expansion.
• When matter is cooled, the opposite happens
and we get contraction.
EVERYDAY EXAMPLES
• Air pressure
• Tires have less pressure in the cold temperatures
• Experiment: two balloons about the same
volume- what will happen when one balloon is
put outside in the cold
EVERYDAY EXAMPLES
• Bridges and sidewalks are built in segments. They have
spaces called expansion joints between them. The
expansion joints allow the concrete and steel to expand
without buckling and cracking.
• The thumping sound you hear when you drive over a
bridge in a car or bus is the sound of the tires going
over the expansion joints.
EVERYDAY EXAMPLES
• Thermometers- liquid in a thermometer will expand with
increased temperatures making them rise
• Global warming is causing ocean levels to rise (due to
the expansion of the volume of water) threatening cities
at sea level
THERMAL EXPANSION
• Substances vary in the amount of thermal
expansion
• Demo in small groups- ring and ball demo
- compound bar
LINEAR EXPANSION- FOR A SOLID
• Depends on the initial length, temperature change, and
the type of materials it is made from
• Change in length (Δ L) is directly proportional to the
change of temperature (Δ T) and the original length
(Lo)
ΔL= α Lo * Δ T
Where: L= length in meters (m); α = coefficient of linear
expansion; Lo= original length (m); Δ T= change in
temperature
EXAMPLE
• A lead rod is 2.5 m long at 20 oC. What is the change in
length if it is heated to 100 oC and α = 27 x 10 -6 oC-1.
SOLUTION
• L =  Lo T
= 27 x10-6 oC-1 x 2.5 m x 80.0 oC
= 0.0054 m
VOLUME EXPANSION- FOR GASES
• ΔV= βVo ΔT
Where: ΔV- change in volume (m3 or L)
β – coefficient of volume expansion
Vo – original length (m3 or L)
ΔT- change in temperature
Note: β is different for different materials
EXAMPLE
• 1000 L of gasoline is in a tank at 20 oC. What is the
change in volume when the temperature drops to 20oC?( β = 950 x 10-6 oC)
SOLUTION
• V= V0T
= 950x10-6oC-1 X 1000L X -40oC
= -38 L
ASSIGNMENT
• do expansion practice problems- check answers
as you go
• Expansion problems- do #1-8