Refrigeration & Air Conditioning Technology, 8e - 30

Unit 2
Matter and energy
O B J E C T I V E S
After studying this unit, you should be able to
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define matter.
list the three states in which matter is commonly found.
define density.
discuss Boyle's law.
state Charles' law.
discuss Dalton's law as it relates to the pressure
of different gases.
define specific gravity and specific volume.
state two forms of energy important to the HVAC/R industry.
describe work and state the formula used to determine the
amount of work done by performing a given task.
define horsepower.
convert horsepower to watts.
convert watt-hours to British thermal units.

✔●Power-consuming devices have the potential to cause injury. Be sure
to de-energize all pumps, motors and other electrical devices before
working on them.
✔●When measuring pressures, be sure that your test instruments are
fully operational and properly calibrated to avoid possible injury.

molecule of water, Figure 2.1. The chemical formula for
water is H2O.
Water in the solid state is known as ice. It exerts all of its
force downward-it has weight. The molecules of the water
are highly attracted to each other, Figure 2.2. When the
water is heated above the freezing point, it begins to change
to a liquid state. The molecular activity is higher, and the
water molecules have less attraction for each other. Water
in the liquid state exerts a pressure outward and downward.
Because water pressure is proportional to its depth, water
seeks a level surface where its pressure equals that of the
atmosphere above it, Figure  2.3. Water heated above the
liquid state, 212°F at standard conditions, becomes a vapor.
In the vapor state, the molecules have even less attraction
Figure 2.1 A water molecule is formed when two hydrogen atoms
bond with one oxygen atom.

OXYGEN ATOM

2.1 MATTER
Matter is commonly defined as a substance that occupies
space and has mass. The weight of a substance is the combined effects of the substance's mass and the force of gravity pulling down on it, where Weight 5 Mass 3 Gravity.
Matter is made up of atoms. Atoms are often described
as the smallest amount of a substance and may combine
to form molecules. Atoms of one substance may combine
chemically with those of another to form a new substance.
These new substances are referred to as compounds. The
molecules formed cannot be broken down any further
without changing the chemical nature of the compound.
Matter exists in three states: solids, liquids, and gases.
The heat content as well as the pressure exerted on matter determine its state. For instance, water is made up of
molecules containing atoms of hydrogen and oxygen. Two
atoms of hydrogen and one atom of oxygen are in each

HYDROGEN
ATOM

HYDROGEN
ATOM

Figure 2.2 Solids exert all their pressure downward. The molecules of
solid water have a great attraction for each other and hold together.

THIS BLOCK OF ICE EXERTS
ALL ITS PRESSURE
DOWNWARD.



Refrigeration & Air Conditioning Technology, 8e

Table of Contents for the Digital Edition of Refrigeration & Air Conditioning Technology, 8e

Contents
Refrigeration & Air Conditioning Technology, 8e - Cover1
Refrigeration & Air Conditioning Technology, 8e - Cover2
Refrigeration & Air Conditioning Technology, 8e - i
Refrigeration & Air Conditioning Technology, 8e - ii
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Refrigeration & Air Conditioning Technology, 8e - Contents
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Refrigeration & Air Conditioning Technology, 8e - Cover4
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