Specific Heat, Heat Capacity, and Calorimetry - PowerPoint Presentation

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)Slide5
Slide6

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: