Work and Heat – Chapter 16
–Heat is the transfer of thermal energy
from one object to another through a
temperature difference.
–HEAT FLOWS FROM HOT TO COLD!!!!
A. Temperature
• Temperature
– measure of the average KE of
the particles in a sample of
matter
– (how fast are the
atoms/molecules moving?)
Temperature
–measure of how hot or cold
something is in relation to amount of
kinetic energy an object has
–SI unit for temperature is Kelvins (K)
Thermal Energy
• Which beaker of water has more thermal
energy?
– B - same temperature, more mass
80ºC
A
80ºC
B
200 mL
400 mL
Heat Transfer
• Heat
– thermal energy that flows from
a warmer material to a cooler material
• Like work, heat is...
– measured in joules (J)
– a transfer of energy
Conduction
–Transfer of thermal energy when 2
materials TOUCH
• Thermal conductors: conduct
thermal energy well
• Thermal insulators: conduct
thermal energy poorly
Convection
–Transfer of thermal energy through
particles flowing around an object
• Heat is circulating (Ovens, ocean
currents)
• OBJECTS NOT TOUCHING FOR HEAT
TRANSFER
Radiation
• Heat transferred through space as a wave of energy.
• Ex. Heat/light from the sun.
• Ex. Heat/light from fire.
Laws of Thermodynamics
–1st Law: Energy can not be
created or destroyed, it can
change onto other forms
–2nd Law: Heat can flow from cold
to hot ONLY if you add WORK
• Example: Refrigerator
Specific Heat Capacity
• Specific Heat = the ability of a substance to
absorb heat energy. (The number of calories
needed to raise the temperature of 1 gram of the
substance by 1 C.)
***Specific Heat Capacity (c) Values are Constant.
(Water has a cp of 1 cal/g x C)
Thermal change (J)= Mass (kg) x T (C) x Specific Heat Capacity (cal/g x C)
Q= m  T  c
Specific Heat Practice Problems
• Find the change in thermal energy of a 20-kg wooden
chair that warms from 15 C to 30 C if the specific
heat of wood is 700 J/(kg C).
• The air in a living room has a mass of 72 kg and a
specific heat of 1010 J/(kg C). What is the change in
thermal energy of the air when it warms from 15 C
to 30 C?