This document discusses heat and energy transfer. It explains the kinetic molecular theory of matter and how heat and temperature differ. Heat is the transfer of energy between objects due to a temperature difference, while temperature is a measure of the average kinetic energy of a substance's particles. The document also covers concepts like specific heat capacity, which is the energy required to change an object's temperature, and latent heat of fusion/vaporization, which is the energy absorbed during phase changes with no temperature change. Heat transfer occurs through conduction, convection and radiation.

1. HEAT AND
ENERGY

2. CONTENTS
• KINETIC MOLECULAR MODEL OF
MATTER
• HEAT &TEMPERATURE
• THERMOMETRY
• SPECIFIC HEAT CAPACITY
• SPECIFIC LATENT HEAT
• HEAT TRANSFER

3. KINETIC MODEL OF MATTER
• The Kinetic Molecular Theory of Matter
states that atoms and molecules possess
an energy of motion (kinetic energy) that
we perceive as temperature. Atoms and
molecules are constantly in motion , and
we measure the energy of these
movements as the temperature of that
substance.

4. Postulates
• The particles with which matter is made up
of are in constant motion.
• Molecular motion is random.
• Particles in motion possess kinetic energy.
• Their motion increase as they gain energy.
• There is an exchange (transfer) of energy
between particles (atoms and molecules)
during a collision between them.

5. Continues…
• Particles (molecules) in gases do not exert
large forces on each other, unless they
are in collision with each other.
• Collisions between these particles are
perfectly elastic.
• Molecular motion is greatest in gases, less
in liquids, and least in solids.
• Solids retain a fixed volume and shape –
particles are tightly packed, usually in a
regular pattern.

6. A few more…
• Liquids assume the shape of the container
which it occupies but maintain their
volume – particles close together with no
regular arrangement.
• Gases assumes the shape and volume of
its container and will expand to fill a
container of any size – particles are very
well far apart with no regular arrangement.

7. Solid liquid and Gas
https://www.chem.purdue.edu/gchelp/liquids/character.html

8. HEAT & TEMPERATURE
ARE THEY ONE AND THE SAME?
IF NOT, HOW WILL YOU EXPLAIN THE
DIFFERENCE?
Boiling water in a pot or a beaker has
more heat energy ?

9. HEAT
• Heat is a form of energy due to the moving
particles.
• It is a scalar quantity.
• It is measured in Joules.
• It can be exchanged between two object if
there is a difference in temperature.
• Heat flows from a hotter object to a cooler
object.
• Heat is the energy in transit.

10. Temperature
• Temperature is an indication of how hot or
cold a body is.
• Temperature doesn’t depends on the
mass of the object/ no of particles .
• It is the average kinetic energy of the
particles.
• It is measured in degree Celsius/
Fahrenheit /Kelvin

11. Thermomertry
• Galileo invented the first thermometer. In his
instrument, the changing temperature of an
inverted glass vessel produced the expansion or
contraction of the air within it, which in turn
changed the level of the liquid with which the
vessel’s long, open-mouthed neck was partially
filled. This general principle was perfected in
succeeding years by experimenting with liquids
such as mercury and by providing a scale to
measure the expansion and contraction brought
about in such liquids by rising and falling
temperature.

12. Thermometer
• An instrument, a thermometer, is required
to measure temperature objectively. The
thermometer makes use of a physical
property of a thermometric substance
which changes continuously with
temperature. The physical property is
referred to as thermometric property.
•

13. Different thermometric
properties and thermometers
THERMOMETRIC PROPERTY THERMOMETER
Volume expansion of a gas Gas thermometer
Volume expansion of a liquid Laboratory or clinical thermometer
Volume expansion of a solid Bi-metallic strip thermometer
Pressure change of a fixed mass of gas Constant – volume gas thermometer
Changes in e.m.f. Thermocouple
Changes in electrical resistance Resistance thermometer or thermistor

14. Thermometry
• A good thermometric property of matter
should vary: continuously with
temperature
uniquely over the range of temperature to
be measured its variation should be
measurable.

15. Developing a thermometer:
• Choose a thermometric substance with a
suitable thermometric properties.
• Select two fixed points which are easily
obtainable and reproducible.
• Divide the temperature range between the
two fixed points into equal divisions.

16. Calibration of thermometer:
• Fixed points are used in calibrating
thermometers. To calibrate a thermometer
is to mark a thermometer so that you can
use it to measure temperature accurately.
A fixed point is a standard degree of
hotness or coldness such as the melting
point of ice or boiling point of water

17. Fixed points in Celsius scale:
• Steam point (upper fixed point) – The
temperature at which pure water boils at
one atmospheric pressure and
is assigned the value of 100 °C.
• Ice point (lower fixed point) – The
temperature at which pure ice melts at one
atmospheric pressure and is assigned the
value of 0 °C.
•

18. Sensitivity of a thermometer:
• Small expansion of the liquid in the liquid
bulb will cause a big change in the length
of the liquid thread in the capillary tube as
it is made narrow. The narrower the bore,
the higher the sensitivity.

19. What happens when we heat a
substance?
• When we heat a
substance it becomes
hotter or changes state.

20. How much heat is needed to raise
the temperature of an object?
• As heat energy increases, temperature
increases. Q∞ Temperature.
• As mass increases, more heat energy is
required to reach the same temperature
• Q ∞ Mass of the object.
• It depends on the material!
• Each material has its own specific heat
capacity (c).

21. Specific Heat (c)
•The specific heat capacity of a
material is the amount of heat energy
required to change the temperature of
1kg of the substance by 1°C/ 1K.
TcmEh ∆=

22. Specific Heat Capacity
TcmEh
∆=
Heat energy (J)
mass (kg)
Change in
temperature (°C)
Specific heat capacity

23. RADIATOR
Why is water used as the coolant?
Because water has a high specific
heat capacity, it can take away a lot
of energy without boiling away.

24. What happens when we heat a
substance?
When we heat the air in a room, the
kinetic energy of the molecules increases.
The air molecules move faster.
When we heat water, the molecules
vibrate faster.
When we heat snow,
the vibration of the
molecules increases
and it eventually
melts.
The temperature does not
always rise!

25. Heating curve/ warming curve

26. Where is the absorbed heat
energy hiding?
• During the melting and boiling the heat
energy is absorbed but the temperature is
not increasing.
• Where does the heat energy go?
• We must supply energy to change a solid
to a liquid or a liquid to a gas.

27. Specific latent heat of fusion:
• When we heat a solid, it will melt and become a liquid.
• At this point, energy is required but the temperature
• does not rise.
• The specific latent heat of fusion of a
• substance is the heat energy required to
• change 1kg of solid at its melting point to
• 1 kg of liquid – without a change in
• temperature.

28. Specific Latent Heat of Fusion
• The specific latent heat of fusion of a
• substance is the heat energy required to
• change 1kg of solid at its melting point to
• 1kg of liquid – without a change in
• temperature.
mlEh
=
Heat energy (J)
mass (kg)
Specific latent
heat

29. Units of Specific Latent Heat
m
E
l h
=
(J)
(kg)
Specific latent
heat J/kg

30. Specific latent heat of
vaporisation
• When we heat a liquid, it will evaporate and become a
gas. At this point, energy is required but the
temperature does not rise.
• The specific latent heat of vaporisation
of a substance is the heat energy
required to change 1kg of liquid at its
boiling point to 1kg of vapour (gas) –
without a change in temperature.

31. • A solid is continuously
heated until it eventually
reaches the gas state.
temperature / °C
time / s
What’s happening
Here? The
temperature of
the solid is rising
What’s happening
here? There’s no
change in
temperature
because there is a
change of state –
the solid is melting
What’s happening
here? There is a
change of state
from liquid to gas
so no change in
temperature
What’s h
here? Al
has turne
the gas t
begins to
What’s
happening
here? The
temperature of
the liquid is
rising

32. Question time
• Calculate the time taken for a 500 W
• heater to melt 2 kg of ice at 0 °C.
• Given that, Latent heat of fusion of ice l =
3.34x105
J/kg
• Specific latent heat of vaporisation=2.26
x105
J/kg

33. Transfer of heat
• Conduction
• Convection
• Radiation

34. Conduction
• Transfer of energy from molecule to
molecule
• Most common in solids
• KE is transferred when particles collide
• MUST have direct contact

35. Convection
• Convection is heat transfer by mass
motion of a fluid such as air or water when
the heated fluid is caused to move away
from the source of heat, carrying energy
with it. Convection above a hot surface
occurs because hot air expands, becomes
less dense, and rises . Hot water is
likewise less dense than cold water and
rises, causing convection currents which
transport energy.
•

36. Radiation
• Thermal radiation is energy transfer by the
emission of electromagnetic waves which
carry energy away from the emitting
object. For ordinarytemperatures (less
than red hot"), the radiation is in
the infrared region of the electromagnetic
spectrum.