Specific Heat Capacity
(SHC)
Sections 21.6 & 21.7
apple pie
Filling gets much hotter than crust
Filling gets much colder than crust
Toppings get much hotter than crust
Toppings get much colder than crust
beach
Sand feels much hotter than water
Sand feels much cooler than water
Same
energy added
Different
∆T
VOCAB
specific heat capacity: amount of heat needed to
raise temperature of 1 gram of a material by 1 °C
Specific heat of water:
4.184 J/(g—oC)
Specific heat of gold:
0.129 J/(g—oC)
Why do different materials have different
specific heat capacities?
One reason is:
Beyond the scope of this course
One way of thinking about it%
• Specific heat capacity – resistance of an object to
change its temperature
– Low SHC = low resistance = fast ∆T
– High SHC = high resistance = slow ∆T
• Which objects have a higher specific heat capacity?
– pie crust / filling
– pizza crust / pizza toppings
– water / sand
Check your understanding
You add 100 calories of heat to 100 grams of water & to a100 grams of iron.
– The water’s temperature goes up only 1 degree.
– The iron’s temperature goes up 20 degrees!
Which material has a high SHC? Why?
Answer: Water b/c lower ∆T
Which objects has a low SHC? Why?
Answer: Iron b/c higher ∆T
Substance
cal/g/oC
or
cal/g/K
Water
1.000
Wood (typical)
0.400
Soil (typical)
0.250
Air
0.250
Aluminum
0.215
Marble
0.205
Glass (typical)
0.200
Iron/Steel
0.108
Copper
0.0924
Silver
0.0564
Mercury
0.0330
Gold
0.0310
Lead
0.0305
SHC of a substance can be used to
help decide which substance should be
used for a specific purpose
• Would you use aluminum or iron to
make pots and pans that heat up
quicker?
Answer:
Iron
(Low SHC = low resistance = fast ∆T)
• Which heats up more slowly: aluminum
or mercury?
Answer:
Aluminum
(High SHC = high resistance= slow ∆T)
Specific heat capacity of water
• Water has the largest specific heat
capacity of all materials.
• 1 cal/g°C or 4.184 J/g°C
• Used in cooling systems in automobiles
and other engines.
– If a liquid with a lower SHC were used instead
of water, the engine’s temp would rise faster
and engine would overheat quickly.
weather
• Because of its high SHC, water tends to
take in heat very slowly, but it also loses
heat slowly.
– Water is warmer than the air during the
winter, and cooler than the air during the
summer.
• Specific Heat Song:
•
http://www.youtube.com/watch?v=JplL0cdcE64&eurl=http://www.markrosengarten.com/chemsong
.html