GAS BEHAVIOUR & GAS LAWS

1. GAS BEHAVIOUR UNDER
CHANGING CONDITIONS
DR. MAHESWARI JAIKUMAR
maheswarijaikumar2103@gmail.com

2. GAS BEHAVIOUR
• All gases generally show similar
behaviour when the conditions are
normal.
• When there is a change in physical
conditions like pressure,
temperature or volume these show
a deviation.

3. GAS LAWS
• Gas laws are laws that analyze the
behaviour of gases under changing
conditions (Temperature, pressure and
volume)
• The variables of state like
the Pressure, Volume and Temperature
of a gas depict its true nature. hence gas
laws are relations between these
variables.

4. THREE PRIMARY LAWS OF GAS
BEHAVIOUR
• Boyle's Law
• Charles' Law
• Avogadro's Law
• (All laws combine into the
General Gas Equation and Ideal Gas
Law).

5. TH GAS LAWS & PRESSURE, VOLUME
AND TEMPERATURE RELATIONSHIP
IS AS FOLLOWS:
• Boyle's Law: The Pressure-Volume Law
• Charles' Law: The Temperature-Volume Law
• Gay-Lussac's Law: The Pressure
Temperature Law.
• The Combined Gas Law.

6. BOYLE’S LAW
• Boyle's law, also referred to as the
Boyle–Mariotte law, or Mariotte's
law, is an experimental gas law that
describes how the pressure of a gas
tends to increase as the volume of
the container decreases.

7. • This law states that at a constant
temperature, the volume (V) of a
given mass of gas is inversely
proportional to its pressure (p).
• At constant temperature, Boyle’s
law can be stated as
V ∝ 1/P or VP = constant ….(1)

8. • The constant is a proportionality
constant.
• Its values depend on the mass,
temperature and nature of the gas.
• If P1 and V1 are the initial values of
pressure and volume of any gas and
P2 and V2 are another set of values,
then we can say that
• P₁V₁ = constant …(2) and P2V2 =
constant …(3)

9. • Since the mass, temperature and
nature of a gas are same
throughout, we say equation (2) and
(3) represent the same quantity.
• Thus we have:
P₁V₁ = P2V2

10. BOYLE’S LAW

11. INTERPRETATION OF VALUES
• P1= first pressure
• P2= second pressure
• V1= first volume
• V2= second volume

12. BOYLE’S LAW -GRAPH

13. CHARLES’S LAW
• Charles's law is an experimental gas law
that describes how gases tend to
expand when heated.
• A modern statement of Charles's law is:
When the pressure on a sample of a dry
gas is held constant, the Kelvin
temperature and the volume will be in
direct proportion.

14. • Charle’s law states that at constant
pressure, the volume (V) of a given
mass of gas is directly proportional
to its absolute temperature (T).

15. • Charles' Law is a special case of
the ideal gas law. It states that the
volume of a fixed mass of a gas is
directly proportional to
the temperature.
• This law applies to ideal gases held
at a constant pressure, where only
the volume and temperature are
allowed to change.

16. EXPRESSION OF CHARLES’S LAW
• Charles' Law is expressed as:
Vi/Ti = Vf/Tf
where
Vi = initial volume
Ti = initial absolute temperature
Vf = final volume
Tf = final absolute temperature
It is extremely important to remember the
temperatures are absolute
temperatures measured in Kelvin, NOT °C or °F.

17. • If V is the volume and T is the
temperature of a gas at some
constant pressure, then V ∝ T or V/T
= constant.
• Following the same method as
above, we can write:
V₁/T₁ = V₂/T₂

18. CHARLE’S LAW

19. INTERPRETATION OF VALUES
• V1= first volume
• V2= second volume
• T1= first temperature
• T2= second temperature

20. CHARLE’S LAW GRAPH

22. GAY-LUSSAC'S LAW
• Gay-Lussac's Law. ... The French
chemist Joseph Gay-Lussac (1778
- 1850) discovered the
relationship between the
pressure of a gas and its absolute
temperature.

23. • Gay-Lussac's Law states that the
pressure of a given mass of gas
varies directly with the absolute
temperature of the gas, when
the volume is kept constant.

24. GAY LUSSACS’ OR
REGNAULT’S LAW
This law states that at constant volume
(V), the pressure (P) of a given mass of a
gas is directly proportional to its
absolute temperature (T).
• We can write: P ∝ T or P/T = constant.
Also, we can write:
P₁/T₁ = P₂/T₂

25. • Gay-Lussac's law states that the
pressure of a given mass of gas varies
directly with the absolute temperature
of the gas, when the volume is kept
constant.
• Mathematically, it can be written
as: {displaystyle {frac {P}{T}}=k}.

28. GAY LUSSAC’S GRAPH

29. AVOGADRO’S LAW
• Avogadro’s Law states that equal
volumes of different gases,
under similar conditions of
temperature and pressure,
contain equal number
molecules.

30. • This means that if you have two
or more different gases, as long
as they have similar conditions
of temperature and pressure,
equal concentrations of these
gases will occupy equal portions
of volume.

31. STANDARD GAS EQUATION
Gases which obey all gas laws under
all conditions of pressure and
temperature are called perfect gases
or the ideal gases.
• Inert gases kept under high
temperature and very low pressure
behave like ideal gases.

32. • Equation of state for a perfect gas can
be written as
PV=nRT ............where,
• P = pressure
• V = volume
• T = absolute temperature
• R = universal gas constant = 8.31 J mol-
1 K-1, n = number of moles of a gas

33. SUMMARY
• Avogadro's law – Relationship between
volume and number of moles of a gas at
constant temperature and pressure.
• Boyle's law – Relationship between pressure
and volume in a gas at constant temperature
• Charles's law – Relationship between volume
and temperature of a gas at constant
pressure
• Combined gas law – Combination of Charles',
Boyle's and Gay-Lussac's gas laws

34. THANK YOU