Transcript - Chemistry Land

Specific Heat
What are the building blocks?
Specific Heat
This concept does not involve building or breaking down
of molecules but might involve a mixture of elements or
compounds.
How water heats up or cools down is
the standard for all other materials.
There is usually an interest to how
metals heat up. However, all materials
heat up differently.
Energy measured in calories is used for this concept.
A calorie is defined as
The amount of heat energy needed to raise the
temperature of one gram of water one degree Celsius.
Or the amount of heat energy lost when one gram of
water cools one degree Celsius.
This calorie is different than the one you hear about
for food. A food calorie is 1,000 times larger. It is
often written with a capital “C”
Specific Heat involves a rate
of heating based on weight
For water, there is one calorie for every one gram and for every
degree Celsius.
One calorie for each gram and for each degree Celsius.
One calorie per gram per degree Celsius.
1 cal
g oC
Observation:
Different materials heat up at different rates.
90OC
1 kg of Aluminum
90OC
1 kg of Gold
20OC
20OC
Gold heats up about 7 times faster than Aluminum
Different materials store different
amounts of heat energy.
90OC
1 kg of Gold
1 kg of Water
20OC
Water takes about 30 times longer to heat than gold,
meaning it stores about 30 times more calories.
90OC
20OC
Explained by the difference of the
specific heat of water versus soil.
Observation:
Different materials heat up at different rates.
90OC
1 kg of Aluminum
90OC
1 kg of Gold
20OC
20OC
Gold heats up about 7 times faster than Aluminum
Different materials store different
amounts of heat energy.
90OC
1 kg of Aluminum
90OC
1 kg of Gold
20OC
20OC
By the time aluminum heats up to 90OC it will have
stored 7 times more calories of heat than the gold did.
Different materials store different
amounts of heat energy.
90OC
20OC
1 kg of Water
1 kg of Aluminum
90OC
20OC
Water takes about 5 times longer to heat than aluminum,
meaning it stores about 5 times more calories.
1 calorie is defined as the amount of
energy needed to raise 1 gram of
water 1 degree Celsius
90OC
20OC
1 kg of Water
1 kg of water would take
1,000 calories for each
degree. Our 700C increase
would take
1,000 x 70 = 70,000 calories.
1 mL or 1 cm3 (cc) of water has the mass of 1 gram.
1,000 mL = 1 Liter has mass of 1 kilogram
90OC
1 kg of water would take
1 kg of Water
1,000 calories for each
degree. Our 700C increase
would take
1 Liter water
1,000 x 70 = 70,000 calories.
70,000 calories = 70 kilocalories
70,000 calories = 70 Calories
20OC
Food calories
The specific heat of water is
1 calorie per 1 gram per 1 degree Celsius
1 cal = Specific Heat
4.184 Joules = 1 calorie g 0C
of Water
Joule = The energy used
by 1 watt for 1 second
1 cal X __ g X __ 0C
g 0C
Let the dimensions tell you how to solve problems.
The specific heat of other materials can be
calculated by measuring the temperature
rise of water.
Blacksmiths may have been the first
to recognize this approach.
Need modern blacksmith
The specific heat of other materials can be
calculated by measuring the temperature rise
of water.
•Grams
Since specific heat
is calories per
gram per degree
(raised/lowered)
we need to keep
track of what
quantities?
•Water
•Metal
•Initial and Final
Temperatures
•Water
•Metal
Conservation of Energy
Energy Lost = Energy Gained
Calories Lost = Calories Gained
Joules Lost = Joules Gained
Winter Survival
and a Safe Source of
Heat
for Field Operations
A request for
investigation into the
heat capacity of
available materials
Problem with heating tents
•
Heating the inside of tents is dangerous because of the potential for
fire and carbon monoxide poisoning. It seems that heating objects
outside the tent and then bringing them inside would be safer.
• Candidates considered for heating are metal objects
like aluminum or iron.
• Rocks found in the vicinity could also be used.
• Water is another candidate.
Water: Pros and Cons
• On a gram for gram basis, water stores heat much more efficiently than
any other candidates. However, water can only be brought to 100
degrees Celsius before it boils, and then it won’t get any hotter unless
placed under pressure, which is dangerous.
• Water is also a precious commodity in some regions, so risking a spill
may not be worth it.
Metal: Pros and Cons
• Some of the metal tools and equipment might be used.
However, in a quick evacuation of camp it might cause
problems if these items are too hot to handle.
Rocks: Pros and Cons
Rocks seem like the best candidate. However, we have no
data on how efficient rocks can store heat, especially of
rocks containing a mixture of minerals.
There are stories of
soldiers and others
who said they
heated up rocks,
brought them into
their tent, and the
rocks warmed up
the tent. This is
good to know, but
there is much
information missing.
Needed questions Where between extremes
What was the mass
of the heated rocks?
Was it a few one-pound rocks or half a ton
of rocks?
How hot were the
rocks?
Were they heated to body temperature or to
several hundred degrees in a fire?
How cold was the
tent?
Was it only a cool 50 degrees Fahrenheit or
a bone-chilling 20 degrees below zero?
How big was the
tent?
Was it a standard one person tent or a large
command post tent?
How much did it
warm the tent?
Did it raise a few degrees or 50 or more
degrees?
Heat energy released by rocks
= Heat energy gained by tent.
To calculate heat energy released from rocks we could
calculate the heat energy gained by the tent, which is
difficult because of the different materials in the tent.
However, we could use water
instead because we know
that it takes one calorie
to raise one gram of water
one degree Celsius.
Heat energy released by rocks
= Heat energy gained by water
In practice, it wouldn’t be that easy to find a rock equal to one gram or to drop it into one
gram of water. Therefore, the calculations will need to adjust for the mass of the rock
and the mass of the water.
Should be
near 100oC
Other heat sources
could be used
(hotplate, stove top,
etc.)
A rock could be heated by a flame but it would be difficult to
measure the rock’s temperature. Another way would be to place the
rock in boiling water and then measure the temperature of the
water. Then the heated rock could be placed in a known amount of
water and the temperature rise of the water could be recorded.
The rock will begin
to cool quickly after
being removed from
boiling water, so the
transfer should be
quick. Also shake off
any excess water so
heating is from rock
and not from the hot
water.
If heat gets
transferred away
from water, then the
water won’t reach its
full temperature.
Therefore, insulation
is critical. Use two
Styrofoam cups.
and a cover.
Name: _________________
It’s February and you want to heat up your pool. It is currently
50oF (10oC) and you want it raised to 80oF (27oC) Using an
electric heater, how much will it cost if 1 kilowatt-hour is 10
cents? The pool is 7.0 meters long, 5.0 meters wide and 2.0
meters deep.
A. What’s the volume in cubic meters? ______
B. What is the volume in cubic centimeters?___________
C. What is the total grams of the water? ____________
1 cc of water weighs 1 gram
A calorie is defined as the energy needed to raise one gram of water one degree Celsius.
D. How many calories will it take to raise the pool water from 10oC to 27oC? _______________
grams 17oC
1 calorie
g. oC
=
E. 1 calorie = 1.1 x 10-6 kilowatts hours. How many kilowatt-hours will you need? ____________
calories
1.1x10-6 kilowatt-hrs
calories
=
_______ kilowatt-hours
$0.10
kilowatt-hr
F. How much will it cost to heat the pool from 50oF (10oC) to 80oF (27oC)? _______________
=
Calories Lost = Calories Gained
calories lost by metal = calories gained by water
grams x SH x
T = grams x 1 cal x
g 0C
grams x SH x (Tf - Ti) =
T
grams x 1 cal x (Tf - Ti)
g 0C
SH x g 0C amount = calories gained by water
g 0C amount
g 0C amount
Specific Heatmetal = calories gained by metal
g 0C