TOPIC: Heat
Learning Standard 4: The Physical Setting
Key Idea 4: Energy exists in many forms, and when these forms change, energy is
conserved.
Objectives
Students will be able to:
-describe the 3 methods of heat transfer and describe how molecules move in
each type
-describe what happens to molecules of a substance as temperature increases
or decreases
-identify the different types of temperature scales and how to convert from
one type to the other
-describe how to measure heat
-describe the 3 types of phase changes and at what temperature each phase
happens
-describe how thermal expansion occurs
Structural Overview
I. HEAT
A. Heat - form of energy caused by the internal motion of molecules of matter (friction)
B. Example: rub hands together  heat
C. Molecules - tiny particles that make up matter
II. HEAT TRANSFER
A. Heat transfer - movement of heat from a warmer object to a cooler one
B. Example: hot pan: heat moves from the hot pan  handle  hand
C. Methods of Heat Transfer
1. Conduction- heat is transferred by the direct contact of molecules
a. fast moving molecules have more heat collide into slow
moving molecules  move faster  collide with slow moving
molecules
b. takes place best in solids (because molecules are in direct
contact with one another)
2. Convection - heat transfer in liquids and gases by means of up and
down movements of molecules called convection currents
a. liquid or gas is heated  molecules move faster  move farther
apart  less dense  rises carrying heat with it
 Example: warm air rises
b. warmer objects and air always move toward colder areas
3. Radiation - heat transfer through space
a. Example: heat energy from the sun, stars, fire
D. conductors
- conduct heat better and more rapidly and permits
electrons to flow freely
a. Example: metals like silver (best conductor)
E. Insulators - substances that do not conduct heat easily and are
made of tightly bound electrons that are unable to flow freely
a. Example: glass, wood, plastic, rubber, air
III. MEASURING HEAT
A. What happens to heat when temperature is changing?
1. increase in temperature  heat is being ADDED
2. decrease in temperature  heat is being REMOVED
B. How is heat measured?
1.Calories – unit of heat
a. joules (1 calorie = 4.19 J)
C. Calorie - amount of heat needed to raise the temperature of 1 gram of water 1C
1. Example: to heat 1 gram of water from 4C to 5C  1 calorie of heat
is needed
IV. TEMPERATURE AND HEAT
A. Temperature - measure of the average kinetic energy (energy of motion) of
molecules
1. adding heat  molecules move faster  increases kinetic energy
2. measure of how cold or hot something is
a. high temperature  fast moving molecules
b. low temperature  slow moving molecules
B. thermometer - instrument for measuring temperature
1. tube filed with mercury
2. when heated molecules move faster and far apart  mercury expands
and rises
3. when cooled, molecules slow down and get closer together  mercury
contracts and drops
C. Celsius Scale - metric temperature scale
1. water freezes at 0
2. water boils at 100
D. Kelvin Scale - metric temperature system using units called kelvins (K)
1. 0 K = absolute zero
2. 273 K = freezing point of water
3. 373 K = boiling point of water
4. absolute zero -lowest temperature that can be reached
E. Converting Celsius to Kelvin
1. Celsius temperature + 273 K = Kelvin temperature
CELSIUS
100
0
-273
KELVIN
Boiling point of water
Freezing point of water
Absolute Zero
373
273
0
V. HEAT AND PHASE CHANGES
A. Phase change - physical change of matter that requires heat energy
1. Example: when an ice cube melts, heat is being absorbed by the ice
B. Freezing Point - temperature at which a substance freezes (liquid  solid)
1. freezing point of water = 0C
C. Melting Point - temperature at which a substance melts (solid  liquid)
1. melting point of water = 0C
D. Boiling Point - temperature at which a substance changes from a liquid to a gas
1. boiling point of water = 100C
E. Temperature during a phase change
1. no change in temperature even though heat is being added or removed
because the average kinetic energy stays the same
F. How does temperature affect solubility?
1. temperature increases the solubility of some substances in water
PHASE CHANGES
Add heat  Energy absorbed by molecules
Melting
SL
SOLID
Evaporation
LG
LIQUID
Freezing
LS
GAS
Condensation
GL
Remove heat Energy released by molecules
VI. THERMAL EXPANSION
A. Thermal expansion - the expansion, or increase in size, if a substance caused
by heat
1. Example: the rising of mercury in a thermometer
2. When do most substances expand?
a. when there temperature is increased