Download Substance Specific Heat Capacity

Thermal Insulators and Conductors
Thermal Conductivity: The ability to conduct
heat.
Thermal Insulators do not conduct heat readily.
Generally, metals have high thermal conductivity
and gases have low thermal conductivity.
Because metals have more “free electrons,” they
are better thermal conductors than materials
that do not have this property such as wood,
styrofoam, and gases.
http://www.youtube.com/watch?annotation_id=annotation_348266&feature=iv&src
_vid=yXT012us9ng&v=vqDbMEdLiCs
For metals, the thermal conductivity is quite
high, and those metals which are the best
electrical conductors are also the best thermal
conductors.
Best conductors
Both heat & electrical
In order:
Silver
Copper
Gold
Aluminum
Kinetic-Molecular Theory
As a substance gets hotter, its molecules move faster!
Faster molecules have higher kinetic energy.
A higher kinetic energy results in a higher temperature!
You may not be able to SEE molecules moving fast without a
microscope, but you can see an increase in temperature
on a thermometer.
Microscopic:
Cannot be seen
by eyes aloneusually you can’t
“measure” the
kinetic energy of the
molecules
Macroscopic:
Can be seen
with eyes aloneyou can
measure the
temperature!
Kinetic-Molecular Theory
As a substance gets hotter, its molecules
move faster!
Faster molecules have higher kinetic energy.
A solid: the molecules are tightly packed
together and move more slowly.
When you add heat…
A liquid: the molecules are not packed as
tightly together and move around.
When you add more heat…
A gas: the molecules are not bound
together and move very fast. When
you add more heat…..
A plasma: the atoms themselves are ripped
apart to become ions.
Since the molecules in aluminum can store more
potential energy than the molecules in gold, the
temperature of gold rises much faster than the
temperature of the same mass of aluminum.
Specific Heat Capacity
• The specific heat capacity, “c”, of a substance is the amount of
heat required per kilogram to raise the temperature by one
degree.
• Different substances have different specific heat capacities
• The higher the heat capacity, the more heat the substance
can “hold” or “give off” with minimal temperature change.
• .
For example, you put 1 kg piece of
steel- about 2 ¼ pounds) on a hot
plate for two minutes. You also
put a container of 1 kg water in on
an identical hot plate.
Would you rather place your finger
on the steel or in the water?
The steel will be at a much higher
temperature!
Both received the same amount of
heat energy.
But water has a higher specific heat
capacity- it can absorb or release
more heat energy with little
temperature change.
http://www.youtube.com/watch?v=yXT0
12us9ng&list=PL908547EAA7E4AE74
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Water has one of the highest specific
heats of all substances. It can absorb and
give off great amounts of heat energy
with little temperature change.
It takes a long time to heat water and it
takes a long time for water to cool down!
Another example: The filling on a hot
apple pie burns our tongues and not the
crust even though they are the same
temperature because of the water
content in the filling.
The filling can give off a lot of heat and
STILL be hot.
Why are our ocean’s so important?
The oceans help maintain a
small range of
temperature on Earth
that is compatible with
life by absorbing heat in
the day and releasing it
at night with little change
in the ocean’s
temperature.
• In contrast, in a desert
there's a wide daily range
of temperature because
the temperature of the
land goes up a lot more
than the ocean for the
same amount of radiation,
• and at night the
temperature goes down a
lot as the land loses
infrared radiation to space.
Substance
The average specific heat
capacity of a human
body is approximately
3500.
Specific Heat Capacity
(J.kg-1.K-1)
water
4200
ice
2100
ethanol
2400
copper
390
aluminium
900
glass
840
mercury
140
wood
1700
lead
130
Heat transfer and temperature change
As heat, Q, flows into or out of a substance, its
temperature change, DT,
will depend on the mass, m, of the substance
and
its specific heat capacity, “c”.
Q = mcDT
Example: How much heat, Q, is required to
raise the temperature of a 3 kg pan of water
from 15°C to boiling temperature?
(specific heat of water = 4180 J/kgK)
Q = mcDT
What is DT? Final – initial =
100° – 15° = 85°
Q = 3 (4180) 85 =
Q = 1,065,900 J
Example: Q = mcDT
Sand has a specific heat of 0.5 cal/gram ̊C. How
many calories does it take to raise the temperature
of 100 g of sand from 60 ̊C to 70 ̊C ?
Q = mcDT
Q = (100) (0.5) (70 – 60)
Q = 500 cal
Example:
• How much would this amount of heat energy
raise the temperature of 100 grams of water?
From the previous problem, Q = 500 cal. We need to know
the specific heat capacity, c, of water that involves calories.
By definition, it is 1 cal/g C.
Q = mcDT
500 = (100)(1) (ΔT)
5 = ΔT
The temperature changes 5 K or ˚C (they both have equal
increments).
• What would the final temperature of the
water be if its initial temperature was 5 ̊C?
Q = mcDT
A 0.2 kg block of metal absorbs 1500 J of heat
when its temperature changes from 20 to
35 degrees Celsius. What is the specific
heat capacity of the metal?
c = Q / (mDT)
c = 1500 / (0.2 • 15)
c = 500 J/kgK