Gas, Ideal Gas, Noble Gas, Boyle's Law - Lecture No-3 - Chemistry - Physics

Topics: Thermodynamics
Subject: Chemistry

Topics: Gas, Ideal Gas, Noble Gas, Boyle's Law

Subject Code: CHM 4201

Lecturer: Mr. Jahedul Islam  

Lecture No- 3

Download Link

Topics of the Chemistry Lecture 3: 

q  Ideal Gas

q  Real Gas

q  Noble Gas

q  Boyle’s Law

q  Charles' Law

q  Diffusion

q  Effusion

q  Dipole – Dipole Interaction

q  Metallic Bond

Ideal Gas

A hypothetical or theoretical gas composed of many randomly moving point particles whose only interaction is perfectly elastic collisions and whose molecules occupy negligible space and have no interactions and consequently obeys the gas laws exactly.

One mole of an ideal gas will occupy a volume of 22.4 liters at STP – 0°C and 1 atm pressure.

The ideal gas equation is: pV = nRT

—Pressure,  p 

—Volume,  V

—Number of moles,  n

—The gas constant,  R

—The temperature,  T

Real Gas  &  Noble Gas

vReal gases are non-hypothetical gases whose molecules occupy space and have interactions; consequently, they adhere to gas laws.

vThe real gas does not behave as an ideal gas due to interactions between gas molecules.

v The noble gases (inert gases) make a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, tasteless, and nonflammable  monatomic gases with very low chemical reactivity.

v The seven noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), the radioactive radon (Rn) and oganesson (Og). 

v Noble gases make up Group 18 of the periodic table. 

Properties of Gases

ü Gases are made up of molecules which are in random motion in straight lines.

ü The molecules behave as rigid spheres.

ü Pressure is due to collisions between the molecules and the walls of the container.

ü That means that there is no loss of kinetic energy during the collision.

ü The temperature of the gas is proportional to the average kinetic energy of the molecules.

ü There are no intermolecular forces between the gas molecules.

ü The volume occupied by the molecules themselves is entirely negligible relative to the volume of the container.

Boyle’s Law

Boyle's law states that, at constant temperature for a fixed mass, the absolute pressure and the volume of a gas are inversely proportional.

  If volume decreases, the pressure increases.

—

Mathematically, Boyle's law can be stated as

    P α 1/V

  or

    PV = k

Where,   P  =  pressure in N/m2

  V   =  volume in dm3 (litres)

  k   =  constant

For comparing the same substance under two different sets of conditions, the law can be usefully expressed as,

        P1V1 = P2V2 

What sort of graphs would this data give?

—If we plot volume directly against pressure we would get a downwards curve showing that volume gets smaller as the pressure gets larger, and vice versa.

What Boyle’s Law Says? 

ÒBoyle’s Law is one of the laws in science that concern the behaviour of gases.

ÒWhen a gas is under pressure it takes up less space.

ÒThe higher the pressure, the smaller the volume.

ÒBoyles Law tells us about the relationship between the volume of a gas and its pressure at a constant temperature.

ÒThe law states that, pressure is inversely proportional to the volume.

Charles' Law 

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.

Charles' Law is expressed as:

V α T    or,

V/T = k

For comparing the same substance under two different sets of conditions, the law can be written as:

V1/T1 = V2/T2

What Charles' Law Says? 

ÒThis Law is one of the laws in science that concern the behaviour of gases.

ÒWhen a gas is heated it takes up more space.

ÒThe higher the temperature, the higher the volume.

ÒIt tells us about the relationship between the volume of a gas and its temperature at a constant pressure.

ÒThe law states that, volume is proportional to the temperature.

Diffusion

qThe movement of particles from regions of higher concentrations to regions of lower concentration.

qEventually, the particles will disperse evenly throughout the space.

qExample: perfume molecules spreading across the room.

Effusion

—Effusion: Gas escaping through a tiny hole in a container or, The passage of a gas under pressure through a tiny opening.

—This depends on the molar mass of the particle, which determines the speed.

q Inter-molecular forces (IMFs) are the forces which mediate interaction between molecules, including forces of attraction or repulsion which act between molecules and other types of neighboring particles.

q There are two major bond types: weak bonds between moleucles, and strong bonds between atoms.

Strong and Weak Bonds

Weak bonds - Van Der Waals Bonds

q All molecules have a weak attraction for each other. This is called the Van Der Waals attraction.

q All liquids and some solids are formed through this kind of weak bond.

q Hydrogen bonds another weak bonds.

Strong bonds - ionic and covalent

q When two atoms bond together very strongly either by a covalent bond or an ionic bond.

q These bonds are much stronger than the weak Van Der Waals bonds that help molecules to stick to each other.

Dipole-dipole Interactions 

v Dipole-dipole interactions are electrostatic interactions between molecules which have permanent dipole(s).

v An example of a dipole-dipole interaction can be seen in hydrogen chloride (HCl) and chloroform (CHCl3):

v The positive end of a polar molecule will attract the negative end of the other molecule and influence its position.

v It happens, when two dipolar molecules interact with each other through space and the partially negative portion of one of the polar molecules is attracted to the partially positive portion of the second polar molecule

Metallic Bond

Metallic bonding is the force of attraction between valence electrons and the metal atoms.

It is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue“. 

A metallic bond is a type of chemical bond formed between positively charged atoms in which the free electrons are shared among a lattice of cations.

Metallic bonding is the main type of chemical bond that forms between metal atoms.

The electrons can move freely within these molecular orbitals, and so each electron becomes detached from its parent atom. The electrons are said to be delocalized. The metal is held together by the strong forces of attraction between the positive protons and the delocalized electrons.

 

This is sometimes described as "an array of positive ions in a sea of electrons".