1. Heat, Temperature, Heat Transfer & Thermodynamics

2. Heat vs. Temperature Heat Temperature A form of energy
Measured in calories or Joules
There is no “coldness” energy
Any object with temperature above zero Kelvin has heat energy
Temperature
Avg. Kinetic Energy of the particles
Measured in C, F, K, R
“hot” & “cold are relative terms
Absolute zero is zero Kelvin

3. Heat Transfer (3 methods)
1. Conduction - requires direct contact or particle to particle transfer of energy; usually occurs in solids
2. Convection - heat moves in currents; only happens in fluid states of matter
3. Radiation - heat waves travel through empty space, no matter needed; IR

4. Thermal Equilibrium
A system is in thermal equilibrium when all of its parts are at the same temperature.
Heat transfers only from high to low temperatures and only until thermal equilibrium is reached.

5. Temperature Scales
There are four temperature scales – Celsius (Centigrade), Kelvin, Fahrenheit, & Rankine
Celsius, C – metric temp. scale
Kelvin, K – metric absolute zero temp. scale
Fahrenheit, F – customary (english) temp. scale
Rankine, R – english absolute zero temp scale

6. Comparing Temperature Scales
All temperatures listed are for water
Celsius - Freezing = 0°C, Boiling = 100°C
Kelvin - Freezing = 273K, Boiling = 373K
Fahrenheit- Freezing = 32°F, Boiling = 212°F
Conversions between Scales
°F = 1.8 *°C+32 K = °C + 273

7. Change of State
steam
vaporization
Heat of fusion
100
condensation
water
Temp ° C
melting
Heat of vaporization
ice
freezing
-20
Increasing Heat Energy (Joules)
As heat is added to a substance it will either be absorbed to raise the temperature OR to change the state of matter.
It can NEVER do both at the same time.
Temperature will NOT change during a phase change!

8. Specific Heat
The amount of heat energy needed to raise the temperature of 1 gram of substance by 1°C.
Substances with lower specific heats change temperature faster.
Symbol : c units : cal/g°C or J/kg°C
For water: c = 1 cal/g°C = 4.18 J/g°C = 4180 J/kg°C

9. Latent Heat
The amount of heat energy required to change the state of 1 gram of substance.
Heat of fusion - latent heat for changes between the solid and liquid phases. Lf =80 cal/g for water
Heat of vaporization - latent heat for changes between the liquid and gas phases. Lv =540 cal/g for water

10. Heat Calculations Q = mL Q = mcΔT Phase Change Temperature Change
Q = heat absorbed or released
m = mass of substance changing phase
L = latent heat of substance
Lf = heat of fusion (liquid solid)
Lv = heat of vaporization
(liquid gas)
Q = heat absorbed or released
m = mass of substance being heated
c = specific heat of substance
ΔT = change in temperature

11. Thermodynamics The study of changes in thermal properties of matter
Follows Law of Conservation of Energy
1st Law – the total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it
2nd Law – natural processes tend to increase the total entropy (disorder) of the universe.

12. 1st Law of Thermodynamics
The total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it.
ΔU = W + Q
ΔU = change in the thermal energy of the system
W = work done on the system (W = Fd or W=ΔK)
Q = heat added to the system
(Q is + if absorbed, Q is – if released)
*All measured in Joules*

13. Heat engines Convert thermal energy to mechanical energy
Require high temp heat source and low temp heat sink. (Takes advantage of heat transfer process)
Examples: Steam engine, Automobile engine

14. Refrigerators and Heat Pumps
It is possible to remove heat from a cold environment and deposit it into a warmer environment.
This requires an outside source of energy.
Examples: Refrigerators, Air conditioning units
Heat pumps are refrigeration units that work in either direction.

15. 2nd Law of Thermodynamics
All natural processes go in a direction that increases the total entropy of the universe.
Entropy is a measure of the disorder of a system.
If heat is added, entropy is increased.
If heat is removed, entropy is decreased.
Work with no ΔT, entropy is unchanged