Transcript Quiz 1 8:30-8:50am TODAY Closed book 7A Final March 18

Quiz 1 8:30-8:50am TODAY
Closed book
7A Final March 18, Tuesday 10:30am-12:30pm
No makeup final/quiz
Chapter 0 = introductory material at the beginning of
the text
• Lecture slides at http://physics7.ucdavis.edu
by ~ 5pm Tuesdays
Due to Monday holiday (1/21),
1/17 Thursday DL Section 1,3,4 cancelled
(DL section 7, 10 meet as normal)
1/18 Friday DL Section 2,5,6 cancelled
Next lecture January 22
Quiz 2 will cover the material from
today’s lecture and DL 3 this week,
excluding FNTs.
ice cream recipes
“A Little House in the Big Woods” way
A VERY quick way
Ice-cube
00 C
00 C
Water
An ice-cube sits in a bath of water.
Water and ice can exchange heat with each other
but not with the environment.
What is the direction of heat transfer?
A. From ice-cube to water
B. From water to ice-cube
C. Impossible to tell
D. Neither of above
Heat
Let us move away from these colloquial terms heat and cool. We
introduce a scientific use of the term heat.
Heat
(Starting definition (to be revised much later))
transfer of energy that takes place from a hot object to a cold one
because the objects are at different temperatures.
Low temp
High temp
Energy leaves hot objects in the form of heat
Energy enters cold objects in the form of heat
If the two objects are at the same temperature, no heat flows
between them.
Ice-cube
00 C
Water
00 C
An ice-cube sits in a bath of water.
Water and ice can exchange heat with each other
but not with the environment.
What is the direction of heat transfer?
A. From ice-cube to water
B. From water to ice-cube
C. Impossible to tell
D. Neither of above
Ice-cube and water are in thermal equilibrium
Thermal equilibrium
If the two objects are at the same temperature, no heat flows between them.
A system in thermal equilibrium
is a system whose temperature is not changing in time.
Low temp
Tfinal
High temp
Energy leaves hot objects in the form of heat
Energy enters cold objects in the form of heat
Reaching Thermal equilibrium
A cup of hot coffee left
in a room…
A thermometer
Cold beer
It can take some time for things to reach thermal equilibrium with its
environment. ~ what is happening at microscopic level? => more to
come when we cover Particle models of thermal energy
Slowing it down
Coffee cup:
ceramic material Beer glass:
glass
A thermometer
Tip:metal
Body:glass, plastic
Q
C=
T
[C] = J/K

Heat capacity of substances:
A measure of the amount of energy required to
increase the temperature of the substance a
certain amount
Heat capacity vs Specific heat capacity
Porcelain
1.1kJ/kgK
Glass
0.84kJ/kgK
Tip:metal
(Silver
0.24kJ/kgK)
Body: plastic
~ 1.2kJ/kgK
Heat capacity is an extensive property:
Heat capacity is an extensive property:
Heat capacity of a pint glass is greater than heat
2kg of water will have twice the heat capacity
capacity of a 3 oz sampler glass
of 1kg water
(i.e. made of same material, more glass material used in a pint glass)
Specific heat capacity is an intensive property:
the
amount
of energy
per
unitdepends
mass/unit
required to
Specific
heat
capacity
only
onmole
the substance
increase the temperature of the substance
by one degree Kelvin
Heat capacity vs Specific heat capacity
Q
Heat capacity of substances: C =
T
A measure of the amount of energy required to
increase the temperature of the substance a
certain amount
[C] = J/K

Specific heat capacity : [Cp] = kJ/kgK
the amount of energy per unit mass/unit mole
required to increase the temperature of the
substance by one degree Kelvin
= kJ/moleK
A note on temperatures
•
•
•
Kelvin: the standard for scientific use.
Increasing the temperature by 1 K =
Increasing the temperature by 10C
Celsius/Centigrade
Same as Kelvin except 0 in a different place
Fahrenheit
Smaller unit of temperature
Heat capacity
in Three-phase Model of Matter
Temperature (K)
Q
C=
T
gas
[C] = J/K
liquid
∆T 
solid
∆E
Energy added (J)
Heat capacity
in Three-phase Model of Matter
Temperature (K)
Q
C=
T
gas
[C] = J/K
Tb

liquid
solid
∆E
Energy added (J)
Heat of vaporazation : ∆H
the amount of energy per unit mass/unit mole
required for a substance to change its phase from
liquid to gas or vice versa
Temperature (K)
gas
Tb
liquid
solid
∆E
Energy added (J)
Heat of melting : ∆H
the amount of energy per unit mass/unit mole
required for a substance to change its phase from
solid to liquid or vice versa
Temperature (K)
gas
liquid
Tm
solid
∆E
Energy added (J)
Typically,
∆Hv >> ∆Hm
e.g. It takes 6 times more energy to vaporize 1kg of water
than to melt the same amount of ice
Temperature (K)
gas
Tb
liquid
Tm
solid
∆E
∆E
Energy added (J)
Example
200C
0.1 kg of water at
is placed in contact with a 2 kg
block of (solid) silver at 2000C. What will happen after
a long time? You may neglect heat that it lost to the
surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, TmSilver =
9610C
Final state of water : L? L+G? G?
Final state of silver : S
What is the final state of water?
0.1 kg of water at 200C is placed in contact with a 2 kg block of (solid)
silver at 2000C. What will happen after a long time? You may neglect
heat that it lost to the surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, TmSilver = 9610C
How much energy is required to raise the temperature of
water to 100 °C?
What is the final state of water?
0.1 kg of water at 200C is placed in contact with a 2 kg block of (solid)
silver at 2000C. What will happen after a long time? You may neglect
heat that it lost to the surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, TmSilver = 9610C
How much energy is required to raise the temperature of
water to 100 °C?
mcwater∆Twater = mcwater(Tfw - Tiw)=(0.1kg)(4200J/kgK)(100°C-20 °C)
= 33.6kJ
What is the final state of water?
0.1 kg of water at 200C is placed in contact with a 2 kg block of (solid)
silver at 2000C. What will happen after a long time? You may neglect
heat that it lost to the surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, TmSilver = 9610C
How much energy is required to raise the temperature of
water to 100 °C?
mcwater∆Twater = mcwater(Tfw - Tiw)=(0.1kg)(4200J/kgK)(100°C-20 °C)
= 33.6kJ
How much energy needs to be removed to decrease the
temperature of silver to 100 °C?
mcsilver∆Tsilver = mcwater(Tfs - Tis)=(2kg)(233J/kgK)(100°C-200 °C)
= - 46.6kJ
Water will reach its phase transition temperature.
Will all the water vaporize?
0.1 kg of water at 200C is placed in contact with a 2 kg block of (solid)
silver at 2000C. What will happen after a long time? You may neglect heat
that it lost to the surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, Hwater= 2257 kJ/kg, TmSilver =
9610C
How much energy is required to vaporize all the water?
mwater∆ Hvapw = (0.1kg)(2257kJ/kg) = 225.7kJ
Will all the water vaporize?
Water will reach its phase transition temperature.
Will all the water vaporize?
0.1 kg of water at 200C is placed in contact with a 2 kg block of (solid)
silver at 2000C. What will happen after a long time? You may neglect heat
that it lost to the surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, Hwater= 2257 kJ/kg, TmSilver =
9610C
How much energy is required to vaporize all the water?
mwater∆ Hvapw = (0.1kg)(2257kJ/kg) = 225.7kJ
Will all the water vaporize?
No
Write out all the possible energy systems
Ethermal,
Ebond,
water
?
water
Ethermal,
Ebond,
silver
silver
?
?
?
We know that the water heats up to 1000C and start
vaporizing while silver cools to 1000C
Ethermal,
Ebond,
water
water
Ethermal,
Ebond,
silver
silver
?
∆EthS + ∆ EthW + ∆ EbW = 0
[-]
[+]
[+]
When heat stops flowing, both silver and water
are at 1000C.
Water is in the mixed phase, silver remains solid.
How much water vaporized?
∆EthS + ∆ EthW + ∆ EbW = 0
[-]
[+]
[+]
mcsilver∆Tsilver + mcwater∆Twater + mwater that vaporized∆ Hvapw = 0
- 46.6kJ + 33.6kJ + mwater that vaporized∆ Hvapw = 0
200C
Example
1 kg of water at
is placed in contact with a 2 kg
block of (solid) silver at 800C. What will happen after a
long time? You may neglect heat that it lost to the
surrounding air in the room.
Note: Csilver= 233J/kgK, Cwater= 4200 J/kgK, TmSilver =
9610C
Final state of water : L? L+G? G?
Final state of silver : S
Closed Book
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