Temperature
• Defined as the measure of the average
kinetic energy of the molecules in a
sample.
1) Increase temperature = increase in KE
Temperature Scale
Scale
Water
Freezes
Water
Boils
Who Uses
Fahrenheit
32°F
212°F
U.S. & one
other country
Celsius
0°C
100°C
Everyone
else. Scale
used in
science
Thermal Expansion
1) Most materials expand when heated
because as the molecules move around
they move apart
2) Thermal expansion is the principle behind
thermometers.
a) expansion of the liquid inside the tube is
proportional to the change in temperature
3) Thermal expansion is used in thermostats.
a) Thermostats use a bimetallic strip to
open and close the circuit.
• Explain why running a spaghetti jar lid
under hot water will allow a person to open
the lid easier than when the jar is cold.
• Underline and use the following terms/
phrases in your explanation.
1) thermal expansion
2) increase temperature
3) increase kinetic energy
4) move apart
Heat
1) Defined as the flow of thermal energy.
2) Heat only exists where there is a
difference in temperature.
3) Heat always flows from hot to cold.
4) Unit of heat is the calorie.
a) calorie is defined as the quantity of
heat needed to raise the temperature of
1 gram of water by 1°C
Changes in Heat
1) Temperature  AVERAGE KE of a sample
2) Thermal Energy  sum (total) of all KE and
PE of the molecules in a substance (PE
comes from energy in bonds)
a) depends on:
1) mass  amount of matter
2) temperature
3) amount of energy the material can hold
Specific Heat
1) Defined as a property of a substance that tells
how much the temperature goes up when a
given amount of heat is applied.
2) The higher the specific heat, the harder it is to
raise the objects temperature
Substance Specific Heat
calorie/g°C
Water
1.00
Ice
0.493
Aluminum
0.215
Silver
0.052
Gold
0.031
Very difficult to raise
the temp of water,
reason why water is
used as a coolant
Easy to raise the
temp because of the
low specific heat
The Heat Equation
Specific Heat
(calorie/g°C)
Heat energy
(calorie)
Q = mcΔT
Mass (g)
ΔT = Tf – Ti
Change in
temp (°C)
If ΔT is negative = heat is lost, Q is negative
If ΔT is positive = heat was gained, Q is positive
Q = mcΔT
Sample Problem: How much heat is needed
to raise the temp of 250 g of water from
20°C to 40°C?
Q = ??
m = 250 g
Q = (250)(1.00)(20)
c = 1.00 calorie/g°C
Q = 5000 calories
ΔT = 40 – 20 = 20°C
• When 300 calories of energy is lost from a
125g object, the temp increases from 40 to
45C. What is the specific heat of this
object?
Q = 300 calories
300 = (125)(c)(5)
m = 125 g
300 = (c)(625)
c = ??
300 = c
ΔT = 45 – 40 = 5°C
625
0.48 = c
• 1200 calories of heat energy is added to a
liquid with a specific heat of 0.57. If the
temperature increases from 20 to 33°C, what
is the mass of the object?
Q = 1200 calories
1200 = (m)(0.57)(13)
m = ???
1200
=
(m)(7.41)
c = 0.57 calorie/g°C
ΔT = 33 – 20 = 13°C 1200
=m
7.41
162 g = m
Flow of Heat and Equilibrium
1) First Law of Thermodynamics  energy
in a closed system is conserved
heat loss = heat gain
When the ice cube goes into the coffee, the
amount of heat lost by the coffee will equal
the heat gained by the ice cube.
2) Thermal Equilibrium  results when
heat flows from a hot object to a cold
object until they are at the same
temperature.
a) heat flow stops once objects reach
thermal equilibrium.
Your grandmother in Ireland send you her
favorite cookie recipe. Her instructions say
to bake the cookies at 190.5°C. To what °F
temp would you set the oven to bake the
cookies
• Formula: F = (9/5 X C) + 32
F = (9 X 190.5) + 32  (1714.5) + 32  342.8 + 32
5
5
 375°F
2) Your father orders a fancy oven from
England. When it arrives, you notice that
the temp dial is calibrated in °C. You wish to
bake a cake at 350°F. At what temp will you
have to set the dial on the new oven?
Formula: C = 5/9(F – 32)
C = 5(350 – 32) 5(318) 1590  177
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3) Your new German car’s engine temp
gauge reads in °C, not °F. You know that
the engine temp should not rise above
225°F. What is the corresponding °C temp
on you new car’s gauge?
Formula: C = 5/9(F – 32)
C = 5(225 – 32)  5(193) 965 107
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A scientist wishes to generate a chemical
reaction in his lab. The temp values in his
manual are given in °C. However, his lab
thermometers are calibrated in F. If his need to
heat his reactant to 232°C, What temp will he
need to monitor on his lab thermometers?
Formula: F = (9/5 X C) + 32
F = (9 X 232) + 32  (2088) + 32  417.6 + 32
5
5
 450°F
You phone a friend who lives in Denmark and tell
him the temp today only rose to 15°F. He replies
that you must have enjoyed the warm weather.
Explain his answer.
He was thinking that the temp was 59F
(because 15°C = 59°F). He did not
understand that 15°F is WAY below
freezing.
A gas has a boiling point of -175°C. At what
Kelvin temp would this gas boil?
Formula: K = C + 273
K = -175 + 273
K = 98
A chemists notices some silvery liquid on the floor in
her lab. She wonders if someone accidentally broke a
Hg thermometer. From her tests she find out that the
melting point for the liquid is 275K. A book says the
melting point of Hg is -38.87 C. Is this substance Hg?
Formula: K = C + 273
K = -38.87 + 273
K = 234
No, the liquid is not Hg b/c the melting points
are different.
You are at a science camp in Fl. It is August.
The 1st question on the quiz involves a
thermometer that reports the current temp as
90°. You need to state which temp scale the
thermometer is calibrated. Which scale do you
pick?
90°C is almost boiling so not that one.
90°C is equal to 363K which is also almost
boiling so its not Kelvin.
90°F is warm but no where near boiling, pick
this one!
1) The weatherman tell you that today will
reach a high of 45°F. Your friend in Sweden
asks what the temperature will be in °C.
What value would you report to your friend?
Formula: C = 5/9(F – 32)
C = 5(45 – 32)  5(13)  65  7.2
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