2. PRESSURE, VOLUME, TEMPERATURE are measurable
properties of gases that are related to each other. If
one of these variables changed, there is a
corresponding change in other variables depending
on its relationship. Gas law equations can be derived
whenever ne of these variables is altered.
3. MAIN
GAS LAWS
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
These laws are
products of various
experiments that are
done many centuries ago.
The Ideal Gas Law can be
used to describe the
relationship between
variables used by the gas
laws.
5. ROBERT BOYLE
• An Anglo-Irish chemist.
• Investigated the relationship between pressure
and volume of a gas using a J-shaped tube
apparatus which was closed to one end.
• He then proposed that, the volume of a given
mass of gas held at constant temperature is
inversely proportional to its pressure.
6. Graph that shows the
relationship of Pressure and
Volume
Schematic Illustration of
Boyle’s Law
7. Boyle has shown us that as the volume decreases,
the pressure increases, which pertains to an inverse
relationship. This relationship is more commonly
called Boyle’s Law. This relationship can be
expressed in a mathematical way: V ∝
1
𝑝
where ∝
means “proportional to”. To change symbol ∝ to an
equal sign, a proportionality constant k, is
introduced. Hence, V = 𝑘1 (
1
𝑝
) or more simply:
PV = 𝒌𝟏
8. For a given sample of gas under two different
conditions at a constant temperature, the product
of pressure and volume is constant , thus, it is
written as follows:
𝑃1 𝑉1 = 𝑃2𝑉2
where 𝑃1 and 𝑉1 are the initial pressure and
volume, while, 𝑃2 and 𝑉2 are the final pressure and
volume of the same amount of gas at the same
temperature.
10. JACQUES ALEXANDRE CHARLES
• A French Physicist
• performed an experiment in a balloon, hot water and cold
water more than 100 years later after Boyle’s experiment
about the volume-pressure relationship.
• He then proposed that “the Kelvin temperature and the
volume of a gas are directly related when there is no
change in pressure of a gas”.
11. Graph that shows the
relationship of Volume and
Temperature
Schematic Illustration of
Charles’ Law
12. From his experiment, Charles has shown us
that as the volume increases and/or
decreases, the temperature manifests the
same increase and/or decreases, which
pertains to a direct relationship. This
relationship is more commonly called Charles’
Law.
13. This relationship can be expressed in a mathematical way:
V ∝ T, or more simply,
V
T
= k, where K is proportional
constant.
For a given sample of gas under two different conditions at a
constant pressure, the equation can be written as:
𝑉1
𝑇1
=
𝑉2
𝑇2
where 𝑇1 and 𝑉1 are the initial temperature in Kelvin and
Volume, while, 𝑇2, also in Kelvin, and 𝑉2 are the final
temperature and volume of the same amount of gas at the
same pressure.
15. JOSEPH-LOUIS GAY-LUSSAC
- A French Chemist and Physicist.
- He proved that one of the postulates in Kinetic Molecular
Theory
is the effect of temperature on the motion of gas
particles.
- Year 1802, he conducted and experiment and discovered
the
relationship between the Temperature and Pressure.
He found out that the pressure of the pressure of a gas increased
or decreased proportionally with a change in temperature. He
summarized his findings in his proposed Gay-Lussac’s Law which
states that “the pressure of a fixed amount of a gas is directly
proportional to the absolute temperature (Kelvin).
16. Graph that shows the
relationship of Temperature
and Pressure
Schematic Illustration of
Gay-Lussac’s Law
17. It can be mathematically expressed as follows P ∝ T
(n, V constant). Or dividing both sides of the equation
by T, hence, P, = k or
P
T
= K.
For any two sets of pressure and temperature, at
constant volume, the equation can be stated as:
𝑃1
𝑇1
=
𝑃2
𝑇2
19. The three properties of a gas (pressure, volume
and temperature) usually change at once under
experimental condition. The four possible
variations are as follows:
1. Both T and P cause an increase in V.
2. Both T and P cause a decrease in V.
3. T causes an increase in V and P cause a
decrease in V.
4. T causes a decrease in V and P cause an
increase in V.
20. The three gas laws (Boyle’s, Charles’ and Gay-Lussac’s laws)
discussed earlier can be combined and may be expressed into
one equation,
PV
T
= K, and expressed as the Combined Gas
Law or the general gas law. Combined Gas Laws allows you to
directly solve for the changes in pressure, volume, or
temperature.
Scientists generally follow the customary reference point of
gases which is 0˚C and 1 atm pressure by international
agreement. This reference point refers to the Standard
Temperature and Pressure or (STP). The temperature can also
be expressed as 273.15 K and standard pressure as 760
torr,760 mmHg and 76 cmHg.
21. The equation can be expressed as follows:
BOYLE’S LAW: V ∝
1
𝑝
CHARLES’S LAW: V ∝ T
COMBINED GAS LAW: V ∝
𝑇
𝑝
or PV ∝ T or PV = constant
Thus,
PV
T
= k
In a constant n, or mole, this can be derived as:
𝑃1𝑉1
𝑇1
=
𝑃2𝑉2
𝑇2
23. • Aside from pressure, volume and temperature, moles may also
be combined to the three properties of gas establish the
relationship among the four variables affecting the behavior of
gases.
• Boyle’s, Charles’s, Gay-Lussac’s and Avogadro’s Law when
combined constitute the ideal Gas Law or ideal gas equation.
24. • The ideal Gas is based on the experimental measurements of the
physical properties of gases: temperature, pressure, volume and
number of moles.
• Ideal Gas equation can be expressed as:
PV = nRT
25. •Where R is the proportionality constant at STP
and is equal to 0.0821 L . atm/mol . K and
referred as the ideal gas constant. This tells that
the volume of a gas varies directly with the
number of moles and absolute temperature and
inversely proportionality with pressure.
