1 Pius Augustine_Calorimetry

1
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Dr. Pius Augustine, S H College https://www.facebook.com/piustine 2
Calorimetry

Thermally agitated molecules
3Dr. Pius Augustine, S H College

Heat
The molecules in a substance are in a
state of random motion.
The energy of random motion of the
molecules of a substance (K.E) is
known as its internal energy
(transferred – heat)
Heat supplied is +ve and given out is -ve 4
Dr. Pius Augustine, S H College

Note : matter does not contain
heat.
Matter contains molecular KE
and PE, not heat.
Heat is energy in transit from
higher temp body to lower
temp body.
Work is energy in transit, but
body does not contain work.5

6

Units of heat
calorie : one calorie is defined as the
quantity of heat energy required to raise
the temperature of 1g of pure water
through 1oC ( from 14.5 oC to 15.5 oC)
1 calorie = 4.186 J
Calorie :(big calorie or Kcal or doctors cal)
Quantity of heat energy required to
raise the temperature of 1kg of pure water
through 1oC ( from 14.5oC to 15.5oC)
1 C a l o r i e = 1 0 0 0 c a l = 4 1 8 6 J7

Which is
largest – J
or calorie or
Calorie 8

Mechanical equivalent
It is the amount of work done
to produce one unit of heat
energy.
It is 4.186 joules per calorie
of heat.
9

Why can’t you establish
whether you are running a
high temperature by
touching your own
forehead?
10

Temperature
It is the average internal kinetic
energy of the molecules of a
substance.
Degree of hotness or coldness of a
body. 11

12

Unit of temperature
SI unit - Kelvin
Other units – oC, oF, oR
K-273 = C-0 = F-32
100 100 180
To convert a particular termperature from one scale to another13

British Thermal Unit BTU
Amount of heat energy required
to change the temperature of
1lb of water by 1oF.
1BTU = 1054 J
14

Calorimetry
Branch of physics which
deals with the
measurement of heat
energy
15

Temperature of water at the
bottom of Niagara falls to be
slightly higher than the
temperature at the top of the
falls? Why?
16

Principle of calorimetry (mixtures )
When two bodies at two different
temperatures are in contact, Heat
energy flows from body at higher
temperature to body at lower
temperature untill both the bodies
acquire same termperature.
17

If the system is fully insulated
from surrounding,
Heat gained by cold body
= Heat lost by hot body.
ie. temperature determines
direction of heat flow.
m1C1ΔT1 = m2C2ΔT2
18

An iron thumbtack and a big iron bolt
are removed from a hot oven. Both
are red-hot and have the same
temperature. When dropped into
identical containers of water of equal
temperature, which one raises the
water temperature more? 19

Heat (thermal) capacity
Amount of heat energy required
to raise the temperature of a
given mass of a substance
through 1oC
Heat capacity C’ = Heat given / rise in temp
C’ = Q/ ΔT
Unit - J/K or J/oC 20

Volumetric heat capacity
s, is the heat capacity
per unit volume
21

• Physical quantity that characterizes
the amount of heat required to
change a body's temperature by a
given amount .
• Bodies were capable of holding a
certain amount of caloric.
• Now it is known that no body contains
heat, but internal energy, therefore
thermal capacity is more apt.
22

Most physical systems exhibit a positive heat
capacity.
There are some systems for which the heat
capacity is negative which results in negative
temperature.
For gravitating objects such as stars , black holes
,etc, Virial theorm gives Upot = -2Ukin
Total energy U = -Ukin
If the system loses energy, for example by
radiating energy away into space, the average
kinetic energy and with it the average
temperature actually increases. The system
therefore can be said to have a negative heat
capacity. 23

cal / oC or kilocal/oC may
also be used
1 cal /oC = 4.2 J/K
Heat capacity = mass x
sp.heat capacity

Specific heat capacity
Quantity of heat energy required to
raise temperature of unit mass of
that substance through 10C(1K)
Specific heat capacity C = C’/m
= Q/ ΔTm
Unit- J/kg/K
Q = mc ΔT 25

•Molar heat capacity: is the
heat capacity per mole of a
pure substance.
•Specific heat capacity
(also called more properly
"mass-specific heat
capacity" or more loosely
"specific heat") 26

Units of C – (J/kg/K) (Jkg-1K-1) (J/kgK) J
kgK
cal/g/oC and kilo cal /kg/oC
Specific heat capacity is a
constant for a given
substance
Water has unusually high
specific heat capacity
Cw = 1 cal/g/oC = 4.2 J/g/oC = 4200 J/kg/K27

Gases have two
specific heats –
at constant
pressure and
constant volume
28

Specific heat capacity of ice
is 2100 J/kg/K (0.5 cal/g/ oC )
Specific heat capacity of
steam = 460 J/kg/K
Specific heat capacity of
Hydrogen = 14630 J/kg/K
(highest )
Human body – 3500 J/kg/K 29

Factors on which heat absorbed
or given out by a body depend
Q = mc ΔT
i. Mass of the body (Q α m)
ii. Specific heat cap of the body
( Q α C )
iii. Magnitude of change in temp.
( Q α ΔT ) 30

Intensive and Extensive property
Intensive property (also called a bulk property,
intensive quantity, or intensive variable, is a
physical property of a system that does not depend
on the system size or the amount of material in the
system: it is scale invariant.
Eg. Sp.heat capacity , density
Extensive property (also extensive quantity,
extensive variable, or extensive parameter) of a
system is directly proportional to the system size or
the amount of material in the system.
Eg. Heat capacity , mass , volume
31

Ratio of two
extensive
properties give
an intensive
property
32

Water equivalent
Of a body is the mass of
water having same heat
capacity as that of the
given body .
Unit is gram(cgs)
33

Calorimeter
34

Calorimeter
35

Calorimeter
• A calorimeter is an experimental device in which a
chemical reaction or physical process takes place.
• The calorimeter is well-insulated so that, ideally, no
heat enters or leaves the calorimeter from the
surroundings.
• Any heat liberated by the reaction or process being
studied must be picked up by the calorimeter and
other substances in the calorimeter.
• A thermometer is typically inserted in the calorimeter
to measure the change in temperature that results
from the reaction or physical process.
• A stirrer is employed to keep the contents of the
calorimeter well-mixed and to ensure uniform heating36

Experimental determination of sp.heat
capacity of a solid insoluble in water
i. Small piece of given solid is weighed (m)
and heated by suspending in a beaker
containing boiling water.
ii. Clean and shining calorimeter with stirrer
is weighed using physical balance (m1)
iii. Calorimeter is filled with 1/3rd water and
weighed again and mass of water is
noted as ( m2), by taking difference.
37

iii.Initial temperature of water in
the calorimeter is noted T1
oC
iv.When solid attains steady
temperature (T2
oC), it is
carefully dropped into the
water in the calorimeter.
v. Contents are stirred well and
final temperature (T) is noted.
38

Apply principle of calorimetry
Heat lost by hot solid = heat gained by
calorimeter + water
mc ( T1 – T) = m1c1 (T-T2) + m2c2 (T-T2)
c – sp.heat capacity of solid
c1 – sp.heat capacity of copper
c2 – sp.heat capacity of water .
39

Q. Adding the same
amount of heat to two
different objects does not
necessarily produce the
same increase in
temperature. Why not?
40

Water is King
when it comes
to thermal
inertia. 41Dr. Pius Augustine, S H College

Water
C = 4.1855 [J/(g·K)]
(at 15 °C, 101.325 kPa)
42

Water has a relatively high specific heat capacity due to
the hydrogen bonding. Hydrogen bonding is a
particularly strong intermolecular force that involves
three major features:
- A large dipole between an H atom and a highly
electronegative atom.
- The small H atom which can get very close to other
atoms.
- A lone pair of electrons on another O, N or F atom, with
which the positively charged H atom can line up.
A major amount of energy is needed in overcoming the
hydrogen bonding. This energy cannot be used to raise
the temperature of water, therefore more energy is
needed to raise the temperature. 43

Advantageous of high specific heat
capacity of water.
i. Land and Sea breezes.
Sp.heat capacity of water(4200J/Kg/K) is
nealy 5 times that of sand and earth.
So land (near sea) gets heated during day
(or cooled during night) much earlier
than water.
This results in drop in pressure over the
land mass during day time and over sea
during night . 44

Advantageous of high specific heat
capacity of water.
ii. Regulation of temperature of body
80% of the human body constitutes
water. Sudden change in the
surrounding temperature does not
affect the heath, because of high
specific heat capacity of water.
Thus protecting animal and plant life.
45

Applications of high specific heat
capacity of water.
i. Fomentation : ( heating swollen parts of
the body at a moderate temperature of
50oC)
Because of high C, water
can store large amount of
heat energy at a fairly low
temperature.
46

47

capacity of water.
Heat reservoir : In cold
countries wine and juice
bottles are placed under
water to avoid freezing .
(water rejects more heat
to bottles as it freezes)48

capacity of water.
Agriculture: Farmers water
their fields before rain in
order to save the crops
from the adverse effect of
50

Because of high C, water liberates large
amount of heat which prevent the
surrounding temp from falling below 0oC
Otherwise, water in the capillaries of plants
freezes to ice, which will break the
capillaries due to anomalous expansion.
51

Wise farmers !!!
52

capacity of water.
Coolant : Flowing water through
pipes around the heated parts of
the machine – radiator, nuclear
reactor etc – remove heat and
cools the machine. 53

54

capacity of water .
Room heater : Hot water is
circulated in pipes
around room to keep
the room hot. 55

Room heater 56

capacity of water.
Wet cloth on forehead.(fever)
Water takes large amount of
heat from head and thus
lowers temperature of
body.
57

Wet kisses serve better
58

It is sometimes injurious to put on
wet clothes. Why?
Because of high C of water,
wet clothes take away large
amount of heat from the body .
Temperature of body may fall
much below the normal
temperature.
59

Water has a
higher thermal
inertia. Explain.

On a hot summer day when atm
temp is 40oC or above, water in a
swimming pool or large lake remains
comfortably cool ( around 25oC ).
why?
∆T = Q/ mc or ∆T α 1/c
Rise in temperature of water will
low due to high C of water .

On clear nights in winter, frost forms
quickly on parked cars. Why ?
When temperature of atm falls, all
bodies radiate heat.
Car being metallic has low C, as
compared to non metallic objects and
cools quickly.
Temperature of car body falls below,
freezing point of water and water
vapour in the atmosphere freezes. 63

A certain quantity of heat is
supplied to both a kg of water and
to a kg of iron . Which undergoes
the greater change in
temperature?
Defend your answer.
64

Both Europe and Canada receive
same amount of heat /km2. But
Europe is not as cold as
northeastern region of Canada.
Why?
65

When a 1kg metal pan
containing 1kg of cold water is
removed from the refrigerator
and set on a table, which
absorbs more heat from the
room - the pan or the water?66

Why does a piece of watermelon
stay cool for a longer time than
sandwiches do when both are
removed from a picnic cooler
on hot day?
67

Base of cooking pan is made thick.
Thermal capacity = mass x C
If thickness is large, thermal capacity
will be also large.
It impart sufficient heat at low
temperature to the bread for its
proper baking. 68

Base of electric iron is thick
Thermal capacity = mass x C
If thickness is large, thermal
capacity will be also large.
It can remain hot for
long duration .
69

Calorimeter is made of thin copper
Thin – less mass
Copper – low sp. heat capacity
Calorimeter has low thermal
capacity.
So contents inside get heat
energy very quickly
70

Change of phase
Solid to liquid - melting
Liquid to solid - freezing
Liquid to gas - vaporization
Gas to liquid - condensation( liquefaction)
Solid to gas - sublimation
Gas to solid - solidification
71

72

73

74

Melting and Fusion
Change of phase from solid to
liquid on heating at a constant
temperature is called melting.
constant temp. - M.P or F.P
Liquid to solid with rejection of
heat is called freezing or
fusion.
75

Vaporization or boiling
Change of phase from liquid to
vapour on heating at a
constant temperature
constant T - boiling point or
ebullition pt ( liquefaction pt)
Gas to liquid with rejection of
heat is called condensation 76Dr. Pius Augustine, S H College

Factors affecting M.P
i.Pressure
ii.impurities
77

Effect of pressure on M.P
substance which contract on
melting ( eg. ice , iron )
M.P decreases by
increase in pres and vice
M.P of ice decreases by 0.0072oC
for every 1atm rise in pressure.
1.091 cm3 of ice 1cm3 of water78

A pressure of 500
atm is needed for
ice to melt at –4 °C.
79

Regelation of ice
Press two pieces of ice together.
on releasing, two blocks appear
stick together. This phenomenon
is regelation of ice.
Reason: when pressure increases ,
M.P decreases and a layer of
water is formed b/w the ice
On releasing M.P rises to 0oC and
layer of water gets frozen.
80

81

Effect of pressure on M.P
Substance which expand
on melting (eg. wax, lead)
M.P increases with
increase in pressure .
1.161cm3 of wax 1.66cm3
(m.p at 64oC ) 82
Dr. Pius Augustine, S H Colleg

Effect of impurities on M.P
M.P decreases by the
presence of impurities
Eg. Kulphies
( freezing mixture made by adding
salt to ice , which reduces the m.p
of ice to -22oC )
Spreading salt over ice on the
roads in cold countries to
remove ice. 83Dr. Pius Augustine, S H College

Which has more kinetic
energy – the molecules
in a gram of ice or the
molecules in a gram of
steam? 84

Vapourisation
Change of phase from liquid to gas
on heating at a constant
temperature( B.P ) is called
vapourisation (Heat is absorbed. )
Reverse is condensation or
liquefaction
Note : all liquids expand on boiling.
( 1cm3 of water at 100oC changes to
1760 cm3 of steam at 100oC ) 85

Effect of pressure on B.P of water
BP of water increases with pressure.
In a pressure cooker P = 1.75atm, water
boils at 120oC to 125oC and such water
above 100oC is known as super heated
water.
At high altitudes , P is less, water boils at a
temperature below 100oC and cooking is
difficult.
Water vapour below 100oC – super cooled
vapour. 86

Effect of impurities on B.P of
water.
Addition of impurities increases
the B.P of a liquid.
Eg. Cooking will be faster when
salt is added. 87Dr. Pius Augustine, S H College

Latent Heat (Q)
LH is the amount of heat energy
aborbed or liberated at constant
temperature during change of
phase of that substance .
It is not a constant for a substance
but depends on mass.
88

Specific latent heat L
Specific LH is the amount of heat
energy aborbed or liberated by unit
mass of a substance at constant
temperature during change of phase
of that substance.
It is a constant for a substance
Latent heat/unit mass
Unit of latent heat is joule and specific
latent heat is J/kg. ( cal/g, cal/kg,
kcal/kg ….)
89

LH – kinetic model
During melting temperature
( average K.E of molecules ) is
constant.
Absorbed energy is used for
increasing the seperation b/w
molecules ( increasing P.E).
In boiling used for increasing
volume against atmospheric
pressure.
90

Specific LH of ice.
Definition :
L.Hice = 336 J/g
336 x 103J/kg
(80 cal/g)
91

Specific LH of steam
Definition :
L.H steam = 2268 J/g
2268 x 103J/kg
(540 cal/g)
L.H steam = 6.75 LHice
92

Natural consequence of high LHice
Slow melting of snow
(large energy from sun is
required)on mountain
avoid flood river keep
flowing through out year.

Sea, river, lakes etc in cold
countries freeze slowly as
large energy need to be
liberated and liberated
energy moderate the
temperature of surrounding. 94Dr. Pius Augustine, S H College

Melting of snow results in
bitter cold as snow
absorbs large heat from
surrounding.

Iceberg persists in sea for
a longer duration.
96

Weather gets moderated
during snow fall.(water
vapor in the atmosphere
freeze and release large
heat energy)
97

Applications of high LHice
i. Use of ice in chilling soft
drinks.
ii. Ice candy is colder than ice
cold water
iii. Water jackets for
preserving fruits and
vegetables.
98

Applications of high LHsteam
i. Steam engine : energy
released during
condensation of steam
gets converted in to
mechanical energy.
ii. Steam pipes for heating
room cold region. 99

Steam at 100oC gives sever burn
than boiling water at 100oC.
As steam condenses on skin
, it releases an additional
energy of 2268 x 103 J of
energy for every kg of water
formed compared to water
at 100oC .
100

Determination of sp.LH by electrical
method.
For change of state of a substance
, heat is supplied by an electrical
heater of known power for t
second.
Energy supplied by heater = P t.
Pt = mL
L = Pt / m
101

Why Specific Latent Heat Of
Vaporization Of Substance Is
Greater Than Its Fusion ?
Increase In Potential Energy
Of The Molecules Is Greater
On Boiling Than On Melting
102

104
Appeal: Please Contribute to Prime Minister’s or Chief
Minister’s fund in the fight against COVID-19
Dr. Pius Augustine, Dept of Physics, Sacred Heart College, Thevara
we will
overcome
Thanks You
http://piusaugustine.shcollege.ac.in
https://www.facebook.com/piustine

1 Pius Augustine_Calorimetry

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