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• Internal energy
• Specific Heat Capacity
• Changes of State
• The Triple Point
• Heat Conduction
• Thermal Resistance
Heat is internal energy in transit from one body of matter
to another by virtue of a temperature difference between
Because heat is a form of energy, the correct SI unit of heat
is the Joule. However, two older units are still used, the
kilocalorie (kcal) and the British Thermal Unit (Btu).
The Kilocalorie and British Thermal Unit
The kilocalorie is the amount of heat required to
raise/lower the temperature of 1 kg of water through
1 kcal = 4185 J
The British Thermal Unit is the amount of heat
added/removed to raise the temperature of 1 lb of
water by 1oF.
1 Btu = 1054 J = 0.252 kcal = 778 ft‐lb
Specific Heat Capacity
The specific heat capacity (symbol c) is the amount of heat
that must be added or removed from a unit mass of the
substance to change its temperature by 1o.
Average specific heat capacities of
Changes of State
Adding or removing heat from a sample of matter does not always lead to a
change in its temperature. Instead the sample may change its state from solid to
liquid or from liquid to gas when heat is added, or it may change from gas to liquid
or from liquid to solid when heat is taken away.
Heat of Fusion and Heat of Vaporization
The heat of fusion of a substance is the amount
of heat added to turn 1 kg of the substance at its
melting point from solid to the liquid state. The
heat of fusion of water is 335 kJ/kg. The symbol
used is Lf.
The heat of vaporization of a substance is the
amount of heat needed to turn 1 kg of the
substance at its boiling point from the liquid to
the gaseous state. The heat of vaporization of
water is 2260 kJ/kg. The symbol used is Lv.
Heat of fusion and vaporization and melting and boiling points
of various substances at atmospheric pressure
The Triple Point
The Triple Point is the intersection
of the vaporization, fusion, and
sublimation curves of a substance.
All three states of a substance may
exist in equilibrium at the
temperature and pressure of its Fusion curve
triple point. Solid
The fusion and vaporization curves Sublimation curve
of water intersect at a temperature
of 0.01oC and pressure of 4.6 torr.
Along the fusion curve, ice and
water can exist together, and along
the vaporization curve, water and
water vapor can exist together.
In conduction, heat is transported by successive
molecular collisions in a body.
Gases are poor conductors, because molecules
are relatively far apart and so do not collide
often. The molecules of liquids and non metallic
solids are closer together leading to somewhat
higher thermal conductivities. Metals exhibit by
far the greatest ability to conduct heat.
Find the rate at which heat flows through an 2.3 ft2‐oF/(Btu/h) pine door
7.0 ft high and 2.5 ft wide when the inside temperature is 70oF and the
outside temperature is 20oF.
Convection is the motion of the a volume of hot fluid from one place to
Convection may be natural or forced. In natural convection, the buoyancy
of a heated fluid leads to its motion. In forced convection, a blower or
pump directs the heated fluid to its destination.
Heat transfer by radiation takes place by means of electromagnetic
waves, which require no material medium for their passage.
In the process of radiation, energy is carried by electromagnetic waves. These
waves travel at the speed of light (3.00 x 108 m/s = 186,000 mi/s) and require no
material medium for their passage.
The figure below shows the classification of electromagnetic waves according to
The greenhouse effect refers to the heating of the earth’s
atmosphere not by direct sunlight but by infrared light
reradiated by the surface and absorbed mainly by
atmosphere carbon dioxide.