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Slide1
Specific Heat, Heat Capacity, and CalorimetrySlide2
https://ed.ted.com/featured/NUUkZ7N3#watch
Turn and talk with your neighbors: What are igloos? Is it counterintuitive that something made of snow can keep us warm?
Video:
How do Igloos Keep Us Warm?Slide3
Turn to your groups: What do you think this means?
Heat Capacity:
The amount of thermal energy necessary in order change the temperature of an object/a substance by 1°C. Adding energy = raising temperatureRemoving energy = lowering temperature
Depends on
size of object and material of which the object is made
Heat CapacitySlide4
The amount of thermal energy needed to raise the temperature of a mass of one kilogram of a substance by one kelvin degree (or one degree
celsius
)Specific because it is the thermal energy per unit mass needed to change the temperature.
Specific Heat Capacity
(c)Slide5Slide6
How many joules of heat must be added to 6.0 kg of water at 10°C to bring it to the boiling point?Slide7
In a closed system, the thermal energy from hotter objects will transfer to the cooler objects until the system has reached a state of thermal equilibrium
The energy removed from one part of the system (and cooling down the temperature) is absorbed/added by another part of the system (causing the temperature to increase).
Thermal equilibrium occurs when all objects in the system have equal temperatures.
CalorimetrySlide8
Q
Thermal Energy (Heat) / J
M Mass / kg
D
T change in temperature (hot – cold) / °C
c specific heat capacity / J·kg
-1
·°C
-1
Keep the temperature change a positive value for all calorimetry calculations set up in this way
Calorimetry: quantifiedSlide9
Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change?
a) the one with the higher initial temperature
b) the one with the lower initial temperature
c) the one with the greater mass
d) the one with the smaller mass
e) the one with the higher specific heat
Question 11.1a
Thermal Contact I Slide10
Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which
one will have the greater temperature change?
a) the one with the higher initial temperature
b) the one with the lower initial temperature
c) the one with the greater mass
d) the one with the smaller mass
e) the one with the higher specific heat
Because the objects are made of the same material, the only difference between them is their mass
. Clearly, the object with less mass will change temperature more easily because not much material is there (compared to the more massive object).
Question 11.1a
Thermal Contact I Slide11
Two different objects receive the same amount of heat.
Explain whether each of
the following choices
is or is not a
reason why the objects may have
different temperature
changes
.
a) they have different initial temperatures
b) they have different masses
c) they have different specific heats
Warm-up:Slide12
Two different objects receive the same amount of heat. Which of the following choices is
NOT
a reason why the objects may have
different temperature changes
?
a) they have different initial temperatures
b) they have different masses
c) they have different specific heats
Question 11.1b
Thermal Contact II Slide13
Two different objects receive the same amount of heat. Which of the following choices is
NOT
a reason why the objects may have
different temperature changes
?
a) they have different initial temperatures
b) they have different masses
c) they have different specific heats
Because
Q
=
m c
D
T
and the objects received the same amount of heat, the only other factors are the masses and the specific heats.
Although the initial temperature is certainly relevant for finding the final temperature, it does not have any effect on the temperature change
D
T
.
Question 11.1b
Thermal Contact II Slide14
Question 11.2
Two Liquids
a)
the cooler one
b)
the hotter one
c)
both the same
Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat?Slide15
Both liquids had the same increase in internal energy, because the same heat was added. But the
cooler liquid
had a
lower temperature
change.
Because
Q
=
mc
D
T
, if
Q
and
m
are both the same and
D
T
is smaller, then c (specific heat) must be bigger.
Question 11.2
Two Liquids
a)
the cooler one
b)
the hotter onec) both the same
Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat?Slide16
The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down?
a) the concrete parking lot
b) the baseball field
c) both cool off equally fast
Question 11.3a
Night on the Field Slide17
The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down?
a) the concrete parking lot
b) the baseball field
c) both cool off equally fast
The baseball field, with the lower specific heat, will change temperature more readily, so it will cool off faster. The high specific heat of concrete allows it to “retain heat” better and so it will not cool off so quickly—it has a higher “thermal inertia.”
Question 11.3a
Night on the Field Slide18
Question 11.3b
Night on the Beach
Water
has a higher specific heat than
sand
. Therefore, on the beach at night, breezes would blow:
a)
from the ocean to the beach
b)
from the beach to the ocean
c) either way, makes no differenceSlide19
Question 11.3b
Night on the Beach
Water
has a higher specific heat than
sand
. Therefore, on the beach at night, breezes would blow:
a)
from the ocean to the beach
b)
from the beach to the ocean
c) either way, makes no differenceSlide20
Question 11.3b
Night on the Beach
Daytime
sun heats both the beach and the water
beach heats up faster
warmer air above beach rises
cooler air from ocean moves in underneath
breeze blows ocean
land
c
sand
<
c
water
Nighttime
sun has gone to sleep
beach cools down faster
warmer air is now above the ocean
cooler air from beach moves out to the ocean
breeze blows land
ocean
Water
has a higher specific heat than sand. Therefore, on the beach at night, breezes would blow:a) from the ocean to the beach
b)
from the beach to the ocean
c) either way, makes no differenceSlide21
Question 11.4
Calorimetry
1 kg of water at 100
°
C
is poured into a bucket that contains
4 kg of water at
0
°
C
. Find the equilibrium temperature (neglect the influence of the bucket).
a)
0
°
Cb)
20
°
C c) 50°C d) 80°Ce) 100°CSlide22
Because the
cold water mass is greater
, it will have a
smaller temperature change
!
The masses of cold/hot have a ratio of 4:1, so the temperature change must have a ratio of 1:4 (cold/hot).
Question 11.4
Calorimetry
1 kg of water at 100
°
C
is poured into a bucket that contains
4 kg of water at
0
°
C
. Find the equilibrium temperature (neglect the influence of the bucket).
a)
0
°
C
b)
20°C c) 50°C d) 80°Ce) 100°C
Q1 = Q2m1c
D
T
1
=
m
2
c
D
T
2
D
T
1
D
T
2
=
m
2
m
1
/
/Slide23
Question 11.5
More
Calorimetry
A 1 kg block of
silver
(
c =
234 J/kg
°
C
) is heated to
100
°
C, then dunked in a tub of 1 kg of water(c = 4186 J/kg
°C ) at 0°
C
. What is the final equilibrium temperature?
a)
0°Cb) between 0°C and 50°C c)
50°
C
d) between 50
°
C and 100
°Ce) 100°CSlide24
Because
c
water
>>
c
silver
it takes
more heat to change the temperature of the water than it does to change the temperature of the silver
.
In other words, it is much “harder” to heat the water!!
Thus, the final temperature has to be closer to the initial temperature of the water.
Question 11.5
More
Calorimetry
A 1 kg block of
silver
(
c =
234 J/kg
°C ) is heated to
100°C, then dunked in a tub of 1 kg of water(c = 4186 J/kg °C ) at 0°C. What is the final equilibrium temperature? a) 0°
Cb) between 0°C and 50°C c) 50°
C
d) between 50
°
C and 100
°
C
e) 100
°
C
Q
1
=
Q
2
mc
1
D
T
1
=
mc
2
D
T
2
D
T
1
D
T
2
=
c
2
c
1
/
/Slide25
How much energy is required to raise the temperature of an empty 20.0 kg iron container from 10.0°C to 90.0°C?
Practice Problem:Slide26
If 200.0 mL of tea (essentially water) that is at a temperature of 95.0°C is poured into a 150.0 g glass teacup (c=840 J·kg
-1·
°C-1) that is initially at 25.0°C, what will be the final temperature of the tea and cup when it reaches thermal equilibrium? Assume all thermal energy remains within the tea and cup system.
Practice Problem #2Slide27
A 0.150 kg sample of a new alloy is heated to 540.0°C and is then transferred quickly to a 200.0 g Aluminum calorimeter cup containing 400.0 g of water. The initial temperature of the calorimeter is 10.0°C. The final temperature of the mixture is 30.5°C. What is the specific heat capacity of the alloy?
Warm-up: