Matter is known to exist in three physical states namely liquid, solid, and gaseous state with the gaseous state being the simplest. A gaseous substance is one in which under normal atmospheric pressure, its boiling point is below room temperature. The Kinetic theory of gases not only accounts for but also explains the general behavior of solids, liquids, and gases in terms of cohesive forces between their particles, and their energies.
Some of the basic postulates of an ideal gas include:
- A gas consists of a large number of tiny molecules moving at random and in straight lines without resting.
- The molecules collide with each other and with the walls of the container
- The actual volume of the gas molecules is very small and negligible, compared to the volume of the container
- During collisions, there are no attractive forces between the molecules; that is, the molecules are completely independent of one another
- Collisions between gas molecules are perfectly elastic ie. there is no loss of kinetic energy
- The average kinetic energy of the molecule is directly proportional to the absolute temperature
General Properties Of Gas
Some of the general properties of gases are outlined below. Note that each property can be explained in terms of kinetic theory:
- A gas can expand and fill any available space; because gas molecules are in continuous motion and never at rest. Hence, a gas has neither a definite shape nor volume.
- A gas has a low density because the intermolecular distance is large i.e molecules are far apart; hence, the molecules can easily be compressed
- Gas molecules can perform three types of motion: vibratory, rotatory, and translator because the molecules are far apart.
- Gas molecules exert pressure. Gas pressure is a function of the frequency of collision between the gas molecules and the walls of the container
- Gas molecules undergo diffusion. This is the process whereby gas molecules move from one region of high concentration to a region of low concentration.
- Gases mix in any proportion
- Under conditions of high pressure and low temperature, gases turn to liquids; the process is called condensation or liquefaction.
Gas Laws In Chemistry
There are various gas laws in Chemistry and this article would outline some of the principal ones that are also common in our everyday life. Some of the principal gas laws include Boyle’s law, Charles’s law, Gay Lussac’s Law, and Dalton’s law of partial pressure.
Boyle’s law states that the volume of a given mass of gas is inversely proportional to the pressure if the temperature is constant. The statement clearly means that at a constant temperature, an increase in the pressure exerted on a fixed mass of gas leads to a decrease in the gas volume and vice versa.
Mathematically: V ∝ 1/P
V = k/P
PV = a constant k
The expression can be written in the form:
[PV = K]m,t
Example
A certain mass of gas occupies 200cm3 at 1.0 * 105Nm-2. Calculate its volume when the pressure becomes 2.0*105Nm-2 at a constant temperature.
From the question above, the following parameters are given:
P1 = 1.0 * 105Nm-2 V1 = 200cm3 P2 = 2.0*105Nm-2 V2= ?
P1V1 = P2V2
Making V2 the subject of the formula, you would have P1V1/P2 = 1.0 * 105 * 200/2.0*105 = 100cm3 .
The second law is Charles law which states that the volume of a fixed mass of gas is directly proportional to the absolute temperature constant pressure.
[V ∝ T]m,P
[V = KT]m,P
[V/T = constant k]m.P
k =constant of proportionality
The evidence to support Charles’s law is an air-filled balloon that expands as the temperature rises at constant atmospheric pressure until it burst.
The next law is Dalton’s Law of partial pressure which originated from John Dalton. The law states that the pressure exerted by a mixture of gases is equal to the sum of their partial pressures provided that the gases do not react at that temperature.
The final law which we would write about is Gay Lusaac’s Law which describes the chemical behaviors of gases. The law states that when gases react, they do so in volumes that bear a simple ratio to one another and to the volume of gaseous products, provided all gaseous volumes are measured at the same temperature and pressure.
Before the end of this article, it was necessary to state Avogadro’s principle because it is also related to gases and is also used for calculations involving gases. The law states that equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of molecules and mathematically, it can be represented by:
V ∝ N