Gases
KMS 8th Grade Science
Ms. Bormann
The Nature of Gases
 The first gas to be studied was air & it was a long
time before it was discovered that air was actually a
mixture of particles rather than a single gas.
 Although air is a mixture of several different gases, it
behaves much the same as any single gas.
 Regardless of their chemical identity, gases tend to
exhibit similar physical behaviors
Characteristics of Gases
The Kinetic Molecular
Theory
 Kinetic = Motion
 Molecular = Molecules
 The theory states the tiny particles in all forms of
matter are in constant motion.
Boyle’s Law
 Robert Boyle was among the first to note the relationship
between pressure and volume
of a gas.
 During his experiments temperature and
the amount of gas were NOT allowed to change.
 Boyle’s Law states The pressure exerted by a gas
held at constant temperature varies
inversely with the volume of the gas.
 For example: If the volume is halved, the pressure would
be doubled
Pressure
Pressure – amount of force exerted per unit of area.
• Pa = Pascal. SI unit for pressure. One Pascal of pressure
is 1 Newton per square meter – therefore a Pascal is a
very small unit.
• kPa = kilopascal. A kilopascal is 1,000 Pa.
Example: At sea level atmospheric pressure is 101.3
kPa. This means that at Earth’s surface, the atmosphere
exerts a force of 101,300 Newton’s on every square
meter (this is about the weight of a large truck)
• Atm = standard atmosphere. 101.3 kPa or 101,300 Pa
Boyle’s Mathematical Law
P1V1 = P2V2
 A gas has a volume of 3.0 L at 2 atm. What is
its volume at 4 atm?
Boyle’s Law
 1. Determine which variables you have
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

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P1 = 2 atm
V1 = 3.0 L
P2 = 4 atm
V2 = ?
 2. Determine which law is being represented P and V = Boyle’s
Law
 3. Rearrange the equation for the unknown variable.
 4. Plug in the variables and solve.
Charles’s Law
 Jacques Charles was among the first to note the
relationship between temperature and volume of a gas.
 During his experiments pressure
and
the amount of gas are NOT allowed to change.
 Charles’s Law states At constant pressure, the volume of
a fixed number of particles of gas is
directly proportional to the absolute
(Kelvin) temperature
 For example: If the temperature is increased, the pressure
will increase
Temperature
Charles' Law must be used with the Kelvin temperature scale.
This scale is an absolute temperature scale. At 0 K, there is
no kinetic energy (Absolute Zero). According to Charles' Law,
there would also be no volume at that temperature. This
condition cannot be fulfilled because all known gases will
liquefy or solidify before reaching 0 K.
oC  273  Kelvin
Charles’s Mathematical Law
 Eg: A gas has a volume of 3.0 L at 127°C.
What is its volume at 227 °C?
Charles’s Law
 1. Determine which variables you have
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
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T1 = 127°C + 273 = 400K
V1 = 3.0 L
T2 = 227°C + 273 = 5ooK
V2 = ?
 2. Determine which law is being represented.
 3. Plug in variables
 4. Cross multiply and solve