ideal-gas

1. Ideal Gas
S.Gunabalan
Associate Professor
Mechanical Engineering Department
Bharathiyar College of Engineering & Technology
Karaikal - 609 609.
e-Mail : gunabalans@yahoo.com

2. Ideal Gas
• An ideal gas is a theoretical gas or imaginary
gas composed of a set of randomly moving,
non-interacting point like particles and they
obeys the gas law always.
An ideal gas is an imaginary gas that obeys gas law under all
conditions

3. Properties of ideal gas
– The gas particles are so small (Point mass) or
nearly zero mass or virtually no volume
– The collision between ideal gases are elastic. i.e.
no attractive or repulsive force during collision

4. Ideal Gas Equation of state
Real gas
Perfect
gas
Ideal gas

5. Ideal Gas Equation of state

6. Ideal Gas Equation of state

7. Gas Constant R
Gas Molar Weight ( M)Kg/Kmol Gas Constant (R )KJ/KgK
Air 28.97 0.287
Nitrogen 28.01 0.297
Oxygen 32 0.260
Hydrogen 2.016 4.124
Helium 4.004 2.077
Carbon dioxide 44.01 0.189
Steam 18.02 0.461
A mole of a substance has a mass numerically equal to the
molecular weight of the substance.
• One g mol of oxygen has a mass of 32 g,
• 1 kgmol of oxygen has a mass of 32 kg,
• 1 kgmol of nitrogen has a mass of 28 kg

8. Ideal Gas Equation of state

9. Ideal Gas Equation of state

10. Ideal Gas Equation of state

11. Units of Pressure
• atmospheric pressure (1 Atm.)
= 1.013 bar,
= 101325 Pascal (Pa = N/m²);
= 760 millimeters of mercury absolute
(mmHgA)
= 760 Torr (1 Torr = 1 mm HgA)

12. Units of Volume & Temperature
• Volume
– m3
– Liter (L)
– CC (Centimeter Cube)
Temperature - always be expressed in
Kelvin scale
T = oC + 273

13. Important Laws of Perfect Gases
01)Boyle's Law
The Volume of a given Mass of a Gas varies inversely as its absolute Pressure,
provided the moles and Temperature remains constant.
02)Charles's Law
The volume of a given Mass of a Gas varies directly as its absolute
Temperature provided the moles and Pressure is kept constant.
03)Gay Lussac law
The Pressure of a given Mass of a Gas varies directly as its absolute
Temperature provided the moles and volume is kept constant.
04)Avogadro's Law
For a given mass of an ideal gas, the volume and amount (moles) of the gas
are directly proportional if the temperature and pressure are constant

14. Important Laws of Perfect Gases
05) Regnault's Law:-
This Law states that "The two specific Heat at constant Pressure (Cp) and
specific Heat at constant Volume (Cv) of a Gas do not change with the change
of Temperature and pressure”.
06) Joule's Law:-
This Law states that "The internal Energy of a given quantity of a Gas
depends on the Temperature".

15. Boyle's Law

16. Charles's Law

17. Gay Lussac law

18. Avogadro's Law
If any two gases have the same pressure, volume and temperature then
they contain the same number of molecules

19. Joule effect and Joule's law
English physicist James Prescott Joule

20. Joule effect and Joule's law
English physicist James Prescott Joule

21. Joule effect and Joule's law
• The magnetostriction effect describes a
property of ferromagnetic materials which
causes them to change their shape when
subjected to a magnetic field.
• Joule first reported observing change in the
length of ferromagnetic rods in 1842
English physicist James Prescott Joule

22. Joule effect and Joule's law
• Gough–Joule effect
– A stretched piece of rubber contracts when heated
• demonstrating this effect is to suspend a weight
on a rubber band sufficient to elongate it at least
50%. When the stretched rubber band is heated
up by an infrared lamp, it does not elongate
because of thermal expansion, as may be
expected, but it retracts and lifts the weight.
English physicist James Prescott Joule

23. Ideal Gas Law Problems
1. you have 10 mol of a gas at 30oC, occupying a
container which is 0.5 L in size. What is the
pressure of this gas in atmospheres?
• Given data
• n = 10 mol
• T = 30oC
• V = 0.5 L
• P = ?

24. Ideal Gas Law Problems

25. Ideal Gas Law Problems
Class Ex: 2. find the volume of 5 mol of gas which is at
350 mm Hg of pressure, and at a temperature of 110 oC.
1 atm = 760 mmHg
? atm = 350 mmHg

26. The specific volume of a substance is the ratio of
the substance's volume to its mass. It is the
reciprocal of density and is an intrinsic property
of matter.
Substance Name Density Specific Volume
Kg/m3 m3/Kg
Air 1.2 0.83
Ice 916.7 0.00109
Water (liquid) 1000 0.00100
Salt Water 1030 0.00097
Mercury 13546 0.00007

27. Note: Molar volume

28. Specific heat

29. Specific heat
• The specific heat - the amount of heat required
to raise a unit mass of the substance through a
unit rise in temperature.
• The product of mass and specific heat (mCv) is
called the heat capacity at constant volume (J/K)
• The latent heat is the amount of heat transfer
required to cause a phase change in unit mass of
a substance at a constant pressure and
temperature

30. Questions
• What is an ideal gas ?
• What is the difference between Universal gas
constant and characteristics gas constant ?

31. Questions

32. Questions

33. Questions
Gas Molar Weight ( M)Kg/Kmol
Air
Nitrogen
Oxygen
Hydrogen
Helium
Carbon dioxide
Steam
Fill the table

34. QuestionsFill the table
S.
No
Symbol Name Units Formulae/ Value
1
2
3
4
5
6 V
7
8 T
9 ρ
10 C

35. Reference
• Rajput, R. K. 2010. Engineering thermodynamics. Jones and Bartlett
Publishers, Sudbury, Mass.
• Singh, O. 2003. Applied thermodynamics. New Age International (P) Ltd.,
Publishers, New Delhi.
• Nag, P. K. 2002. Basic and applied thermodynamics. Tata McGraw-Hill, New
Delhi.
• http://pages.towson.edu/ladon/gases.html
• http://rsnr.royalsocietypublishing.org/content/early/2009/10/12/rsnr.200
9.0038.full
• http://en.wikipedia.org/