Mr. Shields
Regents Chemisty
U03 L04
Heat
Let’s now discuss something called
HEAT and HEAT CAPACITY
70 deg C
30 deg C
Heat is the energy transferred between particles and
the surroundings as a result of a temp. difference
It ALWAYS FLOWS from Hot to Cold.
NEVER from Cold to hot!
Ex. You put a cold pack on your leg. Heat flows from your
leg to the cold pack. Your leg Loses heat so it “feels” cold.
“COLD” DOES NOT FLOW FROM THE ICE PACK
Heat Energy (Q)
• Heat energy results from the movement of
atoms & molecules in matter.
• This Energy depends upon how much of the
substance is present (an extensive property)
• Remember the SI Unit for energy is the
JOULE (calories are used in Eng. System)
1 calorie = 4.184 Joules and
1 calorie (or 4.184J) can raise the
temp of 1g water 1°C
Heat Flow
• Remember …heat always flows from hotter
objects to cooler objects.
H C
• And the Quantity of heat transferred depends on:
• Temperature difference
• Mass of both substances
Hey!
What’s this?
• And the SPECIFIC HEAT of both substances
Specific Heat
Some materials absorb or transfer heat better
than other materials.
Consider what happens to the temperature of a
metal spoon handle vs. a plastic spoon handle
immersed in a cup of hot coffee.
We use cloth pot holders to pick up hot metal pots.
We also use cast iron radiators (not plastic or wood)
to heat our homes by running hot water through it.
The SPECIFIC HEAT of a substance is the amount
of heat required to raise the temperature of 1 g
of the substance by 1 degree centigrade.
1 deg
(Cp)
Also 1 cal
Each substance has it’s own unique
specific heat (Cp)
Specific heats of various Materials
Material
Cp Joules/gram deg C
Aluminum
0.900
Silver
0.230
Gold
0.129
Graphite
0.720
Diamond
0.502
What material
would make Copper
The best
Brass
Radiator?
Iron
Cu, Brass or
Iron?

Materials with
LOW Cp are
Good heat
Conductors
0.385
0.377
0.444
Mercury
0.139
Water
4.184
Ice
2.01
Ethanol
2.46

Which material
Is the best Heat
Insulator?
Specific Heat Equations
HEAT is typically represented by the term “q”
Specific Heat is represented by the term “Cp”
Recall that SPECIFIC HEAT of a substance is the
amount of heat required to raise the temperature
of 1 g of the substance by 1 degree C.
Therefore ….
q = m x Cp x (Tf – Ti)
m = mass
Tf = Final Temperature
Change in Temp
Ti = Initial Temperature
Specific Heat Calculations
Let’s try a problem.
How much heat energy in Joules is needed to raise the
temperature of 30 grams of water from 20 deg. C to 30
deg. C?
Recall that
q = m x Cp x (Tf – Ti)
q = 30 g x 4.18 J/g deg C x (30 deg C – 20 deg C)
q = 125.4 x 10 deg C = 1254 Joules
Specific Heat Calculations
Let’s try another problem.
If 1500 joules are added 100 grams of water at 20 deg C
what is the final temperature of the water?
Heat = mass x specific heat x (final temp – initial temp)
q = m x Cp x (Tf – Ti)
1500 = 4.18 J/g deg C x 100 g x (final temp – 20 deg C)
1500= 418 x (final temp – 20)
Final temp = 3.59 + 20
final temp -20 = 1500/418
= 23.59 deg C