Gas Law in Chemistry

1. Md.Jamil Uddin
Shihab
ID-192800016
Department of EEE
EU
Gas Laws
by

2. The gas is highly compressible and expandable.
As the temperature, pressure and other
quantities change, the volume of the gas
changes drastically. Scientists at different
times have come up with a number of formulas
to explain these effects and other properties
of the gas.
These are
1.Boyle's formula
2.Charles's formula
3.Avogadro's formula
4.Gay Lusak's formula

3. Boyle’s Law
Pressure is inversely proportional to
volume when temperature is held
constant.
P1V1 = P2V2

4. Effect of change in Pressure on the Volume of a
Gas –Boyle’s Law
Pressure and volume are
inversely related at constant
temperature.
𝑃 ∝
P ∝ 1/v
P= K/V
PV=K
P1V1= k =P2V2
P1V1 = P2V2
Father of Mordern Chemistry
Robert Boyle

5. Boyle’s Law:P1V1 = P2V2

6. A Graph of Boyle’s Law

7. Boyle’s Law – Isotherms
• When P of a gas is plotted against V at different
temperature, hyperbola curves are obtained which
are called Isotherms.
• As the temperature increases, the isotherms goes
away from both the axis. This is due to increase
in volume at higher temperature.

8. Charles’s Law
• The volume of a gas is directly proportional
to temperature, and extrapolates to zero at
zero Kelvin.
(P = constant)
Temperature MUST be in KELVINS!

9. Charles’ Law: V1/T1 = V2/T2

10. A Graph of Charles’ Law

11. Effect of change in Temperature on the Volume
of gas – Charles’s Law
• At constant Pressure, volume of given mass of
a gas increase or decreases by decreases by
1/273 times of its original original volume at 0oC
for every 1oC rise
Jacques-Alexandre Charles
1

12. Derivation of Critical Form of Charles’s Law
• Suppose the volume of a gas at 0oC = Vo
𝑜
𝑜
• Volume at 1oC = 𝑉= 𝑉 +
𝑉
1
𝑜
273
𝑜 𝑜
• Volume at 2oC = 𝑉 = 𝑉 +
𝑉
2
𝑜
273
𝑡
• Volume at toC = 𝑉= 𝑉 +
𝑉
𝑡
𝑜
273
𝑜
𝑉𝑡 = 𝑉 𝑜 1
+
𝑡
27
3𝑉
= 𝑉
𝑡
𝑜
273+
𝑡27
3
𝑡 + 273 = 𝑇 𝐾𝑒𝑙𝑣𝑖𝑛 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒
𝑉𝑡 = 𝑉 𝑜
𝑇
𝑡
𝑉 𝑉 𝑜
27
273
𝑇
9

13. Charles’s law - Isobar
When volume of gas is
plotted against
temperature at
different pressures, a
straight line is
obtained.
Each constant pressure
line is called Isobar.
13

14. Absolute Zero
1
• According to Charles’s law: At constant Pressure, volume
of given mass of a gas increase or decreases decreases
by 1/273 times of its original volume at 0oC
• At exact -273 oC the volume of a given mass of gas
reduces to zero.As, -273oC = 0K
• The temperature at which the given volume of a gas
reduces to Zero is called Absolute Zero i.e. 0K or -
273oC.
• Actually all the gases liquefy or
solidify before they reach -273oC.
• This temperature is considered to as the lowest
possible temperature.

15. Absolute Zero Graph:

16. Avogadro’s Law
• At constant temperature and
pressure, the volume of a
gas is directly related to the
number of moles.
V ∝ n
V=Kn
V1/n1=V2/n2
Amedeo
Avogadro
16

17. Avogadro’s Law:
1
V1/n1=V2/n2

18. Avogadro’s Law – Molar Volume
• It has been calculated that if we have 1 dm3 of H2
gas, its mass at STP will be 0.09 g
∴ 0.09 g H2 at STP = 1 dm3
● 2.016g of H2
at STP =1/0.09 x 2.106 = 22.414
dm3
● 2.016g of H2
=1 mol
18
• Hence 1 mol H2 at STP will occupy volume 22.414
dm3
• This volume is called Molar volume.

19. Avogadro’s Law
• Equal volumes of allgases at same
temperature and pressure must
contains equal number of molecules
19

20. Gay Lussac’s Law
The pressure and temperature of a gas are
directly related, provided that the volume
remains constant.
Temperature MUST be in KELVINS!

21. A Graph of Gay-Lussac’s Law

22. Ideal Gases
Ideal gases are imaginary gases that
perfectly fit all of the assumptions of
the kinetic molecular theory.
• Gases consist of tiny particles that
are far apart relative to their size.
• Collisions between gas particles and
between particles and the walls of
the container are elastic collisions
• No kinetic energy is lost in elastic
collisions

23. Ideal Gases (continued)
• Gas particles are in constant, rapid
motion. They therefore possess
kinetic energy, the energy of motion
• There are no forces of attraction
between gas particles
• The average kinetic energy of gas
particles depends on temperature, not
on the identity of the particle.

24. Real Gases Do Not Behave Ideally
Real gases DO experience inter-molecular
attractions
Real gases DO have volume
Real gases DO NOT have elastic collisions

25. Deviations from Ideal Behavior
Likely to behave
nearly ideally
Gases at high
temperature and low
pressure
Small non-polar gas
molecules
Likely not to behave
ideally
Gases at low
temperature and high
pressure
Large, polar gas
molecules

26. The Combined Gas Law
The combined gas law expresses the
relationship between pressure, volume and
temperature of a fixed amount of gas.