Heat
• Objectives
– Be able to distinguish between heat and temperature
– Be able to explain thermal equilibrium
– Identify the three ways heat can be transferred
– Understand specific heat and latent heat
What is Temperature?
Temperature is our measurement of the average
kinetic energy found in the random motions and
vibrations of countless atoms and molecules.
Temperature is a way of quantifying the kinetic
energy of these atoms and molecules.
Temperature is Energy.
Maxwell-Boltzman Velocity Distribution
Higher temperatures
mean higher
velocities for
atoms and
molecules
Heat Transfer
Three Modes of Heat Transfer
Radiation
Convection
Conduction
Radiation
Energy transport via electromagnetic waves
Convection
Energy transport by mass motion
Conduction
Energy transport by vibrational translation
The jostling of atoms and
molecules in close proximity
in a solid, especially one with
high conductivity.
Specific Heat
• Q = m c DT
Q = HEAT ENERGY
m = mass
DT = Temperature difference
c = specific heat responsible for the thermal
properties of the substance
(Joules/kg/Celsius)
DT = Q/mc
Specific Heat
DT = Q/mc
For a given amount of heat energy, say 10,000 Joules,
what is the temperature change for 1 kg of water and
1 kg of sand?
Csand = 838 J/kgoC
Cwater = 4186 J/kgoC
DTsand = 10,000/1(838) = 11.9 oC
DTwater = 10,000/1(4186) = 2.4 oC
Heat Energy
Changes of State
Energy Increased and Absorbed by Substance:
• SOLID to LIQUID
Melting
• LIQUID to GAS
Boiling
• SOLID to GAS
Sublimation
Energy Decreased and Released by Substance:
• GAS to SOLID
Deposition
• GAS to LIQUID
Condensation
• LIQUID to SOLID
Freezing
Latent Heat
Latent Heat of Fusion
Heat Energy required to
convert solid to liquid
Lf
Latent Heat of Vaporization
Heat Energy required to
Lv convert liquid to gas.
Melting
DT = Q/mc
Amount of heat energy needed to bring a 25 g ice
block to a temperature of 50oC?
Starting Temp = 0oC
Ending Temp = 50oC
Q = heat needed to make transition from ice to water
+ heat needed to heat water from 0 to 50 oC
Q = mLf + mcDT
Melting Ice
Q = m Lf + m c DT
Q = heat needed to make transition from ice to water
+ heat needed to heat water from 0 to 50 oC
= 80 cal/g*(25 g)*(4.186 J/1000 Cal)
+ 25 g *4.186 J/goC *(50-0 oC)
= 8.37 J + 5230 J
= 5238.4 J
Temperature Conversions
CELCIUS
C = 5/9 (F-32)
FAHRENHEIT
F = (9/5 C) + 32
ABSOLUTE
or KELVIN
K = C + 273