SOURCES OF HEAT
A. NATURAL SOURCES
1. The sun
2. The interior of the Earth
B. ARTIFICIAL SOURCES
1. Chemical Action
2. Mechanical Energy
3. Electrical Energy
4. Nuclear Energy
UNITS FOR TEMPERATURE
1. Fahrenheit Scale (oF) – Fahrenheit
temperature scale is a scale based on 32 for
the freezing point of water and 212 for the
boiling point of water, the interval between
the two being divided into 180 parts. The
18th-century German physicist Daniel
Gabriel Fahrenheit originally took as the zero
of his scale the temperature of an equal icesalt mixture and selected the value of 98.6 for
normal body temperature.
2. Celsius Scale (oC) - is based on 0 for the
freezing point of water and 100 for the
boiling point of water. Invented in 1742 by
the Swedish astronomer Anders Celsius, it is
sometimes called the centigrade scale
because of the 100-degree interval between
the defined points.
3. Kelvin (K) - Kelvin temperature scale is the base
unit of thermodynamic temperature
measurement in the International System (SI) of
measurement. It is defined as 1/ 273.16 of the
triple point (equilibrium among the solid, liquid,
and gaseous phases) of pure water. Zero point
absolute zero, the theoretical temperature at
which the molecules of a substance have the
lowest energy. The kelvin has the same
magnitude as the degree Celsius.
TEMPERATURE CONVERSION
FACTORS
MODES OF HEAT TRANSFER
1. CONDUCTION - transmission of heat across matter
2. CONVECTION - the internal movement of currents
within fluids(i.e. liquids and gases).
3. RADIATION - heat from the movement of charged
particles within atoms is converted to electromagnetic
radiation; transfer doesn’t require a medium.
EFFECTS OF HEAT
1.
2.
3.
4.
5.
Change in temperature
Change in phase
Change in size
Chemical change
Change in bodily functions of living
organisms
CHANGE IN TEMPERATURE
Heat capacity – quantity of heat energy
needed to raise the temperature of a given
quantity of substance by 1o C.
- dependent on the identity of the substance
and its mass
Specific heat capacity - quantity of heat
energy needed to raise the temperature of 1
gram of a substance by 1o C.
- dependent on the identity of the substance
CHANGE IN TEMPERATURE
H = c m ΔT
H = Enthalpy = amount of heat energy in
joules (J)
c = specific heat ( J/g-oC)
m = mass in grams (g)
ΔT = change in temperature (Tf-Ti) (oC)
Substance
Specific heats
(c) and molar
heat capacities
for various
substances at
20 C
c in J/gm K
Molar C
J/mol K
Aluminum
0.900
24.3
Bismuth
0.123
25.7
Copper
0.386
24.5
Brass
0.380
...
Gold
0.126
25.6
Lead
0.128
26.4
Silver
0.233
24.9
Tungsten
0.134
24.8
Zinc
0.387
25.2
Mercury
0.140
28.3
2.4
111
Water
4.186
75.2
Ice (-10 C)
2.05
36.9
Granite
.790
...
Glass
.84
...
Alcohol (ethyl)
TEMPERATURE CHANGE
How many joules of heat will be needed to raise the
temperature of 200.0 g of Al from 27.0oC to 80.0oC?
H = c m ΔT
c = 0.900 J/g-K
m = 200 g
ΔT = (80-27) oC = 53 oC = 53 K
H = (0.900 J/g-K ) (200 g) (53 K) = 9540 J