Name: _____________________
Period: _____________________
Temperature (T) —a measure
of the average internal energy
of the substance. As internal
energy changes, temperature
changes. Higher T = more U.
Basic Definitions
Internal Energy (U)— the energy
inside an object due to the kinetic
energy (motion) of the molecules.
More U = higher T.
Cold atoms are
moving slow.
Because they are at the
same temperature no
energy is being transferred:
Q = 0, but T ≠ 0
Heat (Q) — energy transferred between objects of different temperatures. +Q = heat is
added, which causes a raise in temperature;
−Q = heat is removed, which causes a lower
temperature. T ≠ Q. Temperature is not
heat! Temperature can change without
heat—by stirring, for instance, because it
increases the internal energy of the substance.
Hot atoms are
moving quickly.
The cold atoms may have more total
energy because there are more atoms.
Temperature Scales
Heat 1
Heat
Celsius/Fahrenheit conversions
TF = 95 TC + 32.0
−Q
Q always moves from hot
to cold. Q is + if gained;
Q is −if energy is lost.
Boiling point
of H2O (at 1 atm)
Fahrenheit
32ºF
212ºF
Celsius
0ºC
100ºC
Kelvin
273K
373K
TK = TC + 273
0K
The specific heat of a substance measures how hard it is to
change temperature. It is like temperature inertia. Objects
with high cp resist a change of temperature.
Gold (a very good
conductor) has a low
cp (0.129 J/g•ºC), so
it takes very little
heat to change its
temperature.
Gold—low cp
Water—high cp
Heat Transferred During a Temperature Change
Mass (in g)
Heat
(in J)
Example: How much heat is lost
by a 10 kg iron skillet when it is
removed from 180ºC oven (350ºF)
and cools to room temperature
24ºC (75ºF)?
cstephenmurray.com
40ºC
+Q
Freezing
point of H2O
Celsius/Kelvin conversions
Water has a very high cp
(4.186 J/g•ºC) so it can hold
a lot of heat and requires a
lot of heat to change its temperature. Insulators tend to
have high specific heats.
The amount of heat absorbed or released by an
object depends on the
object’s mass, specific
heat, and the change of
temperature of the object.
15ºC
Scale
The lowest possible temperature is absolute zero: 0K, −273º C, −459ºF. At
absolute zero objects have no internal energy (U = 0 J) and atoms are still,
meaning they have no kinetic energy. Matter acts very strangely at and near
absolute zero.
Calculating Heat
35ºC
We are bad judges of temperature, so we use thermometers to measure temperature for us.
The metal feels colder
because it is a conductor. The wood handle
feels warmer because
it is an insulator. Actually, they are at the
same temperature.
Specific Heat—Cp
35ºC
Specific Heat (in J/g•ºC)
Q = mcp ∆
T
(T – T )
f
m = 10kg (10,000g)
Ti = 180ºC
Tf = 24ºC
cp = 0.448 (iron)
i
Change of
Temperature
(in ºC)
This object has no
internal energy:
it is at absolute zero.
Substance Cp (J/g·ºC)
aluminum
0.900
copper
0.387
gold
0.129
iron
0.448
steam
2.010
ice
2.090
water
4.186
A hot tub requires a lot of
heat (Q) to raise the water’s
temperature. There is lot of
water (big m) and water has
a high cp. If the water is cold
to begin with, then the low
initial temperature would
mean even more Q, since
there would be a large ∆T.
Q = mcp∆T
Q = mcp(Tf – Ti)
Q = 10,000(0.448)(24 – 180)
Q = 4480(−156)
Q = −6.99x105 J
(− means heat is lost)
Copyright © 2010, C. Stephen Murray
Name: _____________________
Heat 1
Period: _____________________
6. Kelvin
A. Measures how hard it is for a substance to
change temperature.
2. Temperature B. A measure of the internal energy of a substance. Not equal to heat.
3. Internal
C. Energy transferred between objects due to
Energy
a change of temperature.
4. Q
D. Energy due to motion. More of this =
more internal energy.
5. Kinetic
energy
E. Variable for heat.
7. Absolute
zero
B. Temperature scale used in science that is
based on absolute zero.
8. Specific
Heat
C. The coldest possible temperature, where
all atoms stop moving.
9. Fahrenheit
D. Temperature scale used in the United
States. Water boils at 212º; freezes at 32º.
10. Celsius
E. Temperature scale based on phases of
water: boiling = 100º freezing = 0º.
11. Which of the following has more internal energy?
A. Hot cup of water or a cold ocean?
15. Is Q positive or negative?
A. ___ If an object gains energy.
B. ___ If an object loses energy.
C. ___ If an object is surrounded by a colder object.
D. ___ U increases.
1. Heat
A. Amount of energy in an object due to the
internal motion of the atoms and mass.
B. A hot frying pan or a cold frying pan?
C. 25 kg of water or 25 kg of gold at thermal equilibrium?
D. Fast moving or slow moving atoms?
12. Give two examples of changing temperature without
adding heat.
13. Kelvin, Celsius, or Fahrenheit?
A.____ 0º = the freezing point of water.
B.____ 212º = boiling point of water.
C.____ Used all around the world.
D.____ Used only in science.
E. ___ 373 = the boiling point of water.
F. ___ Based on absolute zero.
16. Given 1000 J of heat, which will gain more temperature?
A. Copper or gold?
B. Ice or steam?
C. Ice or water?
D. Aluminum or iron?
17. How much energy is need to raise 50 g of water from
45º C to 80ºC?
18. 12 g of gold at 90ºC cools to 20ºC. How much heat is
given off?
14. Convert the following:
A. 98.6º F to Celsius.
19. A piece of aluminum requires 4,000 J of energy to change
from 68ºC to 110º C. How much aluminum is there?
B. 35º C to Fahrenheit.
20. 5x104 J of heat are added 35 kg of water initially at 12ºC.
What is the water’s final temperature?
C. 40ºC to Kelvin.
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Copyright © 2010, C. Stephen Murray