Behavior of Gases Can we liquefy the Earth’s atmosphere? And do you know the behavior of gases under very low temperature? Are there any laws that govern the behavior of gases? Here we shall learn about the various interesting properties of gases. Read out more in this section. Behavior of Gases There are 5 main states of matter: solid, liquid, gas, plasma and the Bose-Einstein condensate. Out of these gases are a special state. Their properties are easy to study. We see that gases follow certain laws known as the gas laws. These laws tell us about the behavior of gases. By that, we mean the values and relations of temperature, pressure and volume etc. Let’s see what these laws are. Browse more Topics under Kinetic Theory ● Specific Heat Capacity and Mean Free Path ● Law of Equipartition of Energy ● Kinetic Theory of an Ideal Gas Gas Laws
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Behavior of Gases...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
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Behavior of Gases
Can we liquefy the Earth’s atmosphere? And do you know the
behavior of gases under very low temperature? Are there any laws that
govern the behavior of gases? Here we shall learn about the various
interesting properties of gases. Read out more in this section.
Behavior of Gases
There are 5 main states of matter: solid, liquid, gas, plasma and the
Bose-Einstein condensate. Out of these gases are a special state. Their
properties are easy to study. We see that gases follow certain laws
known as the gas laws. These laws tell us about the behavior of gases.
By that, we mean the values and relations of temperature, pressure and
In the periodic table of elements, we have the group of inert gases or
permanent gases which are very unreactive. Their properties are very
close to an ideal gas and hence their behavior resembles that of an
ideal gas. On the basis of certain experiments using inert gases, the
following laws governing the behavior of gases were established:
Boyle’s Law
Suppose you have some Helium in a gas container at a low pressure
and temperature. At a constant temperature, if you increase the
volume of the container, the pressure of the gas will decrease. This is
given by the Boyle’s law.
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)
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)
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
Charles’ Law
A similar relation is found between Volume and Temperature of an
ideal gas. We call it the Charle’s Law. This law states that at constant
pressure, the volume (V) of a given mass of gas is directly
proportional to its absolute temperature (T).
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
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
Kinetic Theory of Gases
Avogadro’s Law
This law stat
es that equal volumes of different gases, under similar conditions of
temperature and pressure, contain equal number molecules. 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.
For example, at STP (Standard Temperature and Pressure) or NTP,
where T = 273K and p = 1 atm, 22.4L of each gas has NA = 6.023 x
10^23 molecules. In other words, one mole of any gas under STP
conditions occupies 22.4L volume.
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.
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
Real Gases
None of the gases that exist in nature, follow the gas laws for all
values of temperature and pressure. So we see that the behavior of
gases that exist or the “real gases” differs from the behavior of the
ideal gases. These gases deviate from ideal gas laws because:
● Real gas molecules attract one another.
● Real gas molecules occupy infinite volume.
Hence the equations for such gases need modifications as discussed
below.
Real Gas Equation or Van der Waal’s Gas Equation
The equation of state for a real gas can be written as:
(P + a/V²) (V-b) = RT
where, a and b are Van der Waal’s constants.
Solved Examples For You
Q: Assertion: If the pressure of an ideal gas is doubled and volume is
halved, then its internal energy will remain unchanged.
Reason: The internal energy of an ideal gas is a function of
temperature only.
A. Both the Reason and Assertion are correct and Reason is the
correct explanation of Assertion.
B. Both are correct but Reason is not the correct explanation of
Assertion.
C. The assertion is correct but Reason is wrong.
D. The reason is correct but Assertion is wrong.
Solution: A). Let P’ = 2P and V’ = V/2. Then from the equation of the
state, P’V’ = nRT, we have from substitution PV = nRT. This shows
that temperature doesn’t change and as the Internal energy of an ideal
gas is a function of Temperature only, the internal energy of the gas
will remain same.
Specific Heat Capacity & Mean Free Path
Let us say that we want to heat equal weights of an iron rod and water.
After say 5 minutes, which of the two will be at a greater temperature?
The answer is the iron rod. But why is it so? The answer lies in the
Specific Heat Capacity of the substances. Different substances accept
heat differently. Let us learn more!Specific Heat Capacity
Specific Heat Capacity is the amount of energy required by a single
unit of a substance to change its temperature by one unit. When you
supply energy to a solid, liquid or gas, its temperature changes. This