Showing posts with label Class Notes: Chemistry. Show all posts
Showing posts with label Class Notes: Chemistry. Show all posts

### Molarity (M):

Molarity is defined as the number of moles of solute per litter of solution. That is,

Here,
W = weight of solute.
M = molecular mass of solute
V = volume of solution

### Show that the half-life of a second order reaction is inversely proportional to its initial concentration.

For the simple second order reaction 2A→product, we know the rate constant is given by,

For half life,  and

Hence,

as k is a constant,

### Derive an expression for the rate constant of 2nd reaction of the type, 2A→product.

2A → Product
initial concentration : a molL-1                       →                              0
final concentration (t=t) : (a-x) molL-1             →                  x molL-1

Integrating,

### Derive an expression for the rate constant of a first order reaction. Give its units.

Let us consider a first order reaction,

A → product

Suppose at the beginning of the reaction, that is, when t=0, the concentration of A is amolL and when t=t, the concentration of A is (a-x)molL.

For a first order reaction, the rate of reaction,

where k is the rate constant.

integrating,

Here, c is the constant of integration.

### Order:

Order of a reaction is defined by the number of atoms or molecules, whose concentration change during the reaction and determine the rate of the reaction.

For example,

It is a first order reaction.

It is a second order reaction.

### Example of Dry Cell - Leclanche Cell:

The most common example of dry cell is Leclanche cell invented by French scientist Georges Leclanche. We use to call it a battery. It has a cylindrical Zn container which works as the anode. At the center of the Zn container a carbon or graphite rod is placed vertically in a mixture of MnO2 and graphite powder. The Zn container is then filled up with a paste of ZnCl2 and NH4Cl. The above described Leclanche cell may be represented as follows,

### Chemical bond

Atoms of all elements except of the inert gasses have a tendency to combine either with each other or with the atoms of other elements to form cluster of atoms with definite composition. A cluster formed may be either a molecule or an ion. The attraction between the atoms forming the cluster is called a chemical bond.

### Diamond

Diamond is an allotrope of carbon. Due to difference in bonding in its structure, it looks quite different from the other allotropes. Each carbon atom of diamond is sp3 hybridized. The four sp3 orbital arrange themselves in the four corners of a tetrahedron. Each orbital forms a bond with an orbital of another carbon atom. So, in diamond, each carbon atom surrounded by four carbon atoms arranged tetrahedral forming a giant three dimensional molecule. All the electrons in the outer most shell of each carbon atom is engaged in covalent formation. So, no free electron is found, which makes diamond a non-conductor of electricity. It is also transparent to X-ray and white light as there are no free electrons to encounter with X-ray or white light. Due to its firm rigid arrangement of the carbon atom, with bond distance of 1.54 A, diamond is the hardest substance found in naturally.

Also it needs a high amount of energy to break the bonds between the carbon atoms to turn it into liquid. So its melting point is very high (3500°C) and its density is 3.5.

### Briefly explain the formation of dimmers and trimmers.

Some compounds like hydrogen fluorides, ethanoic acids, benzoic acid form dimmers or trimmers by joining up of their two or three molecules by H-bonding. Sometime, due to the formation of these dimmers or trimmers the molecular weight of these compounds appears to be doubled or tripled. That is, ethanoic acid has molecular weight of 60, but in a dimmer of this molecule the molecular weight appears to be 120.

### Atomic spectra:

When a ray of light is passed through a glass prism, it is dispersed into a band of seven colors. This is called a spectrum.

When a gas or vapor is heated to a high temperature or subjected to electric discharge, it emits light of all wavelengths. This light, if passed through a prism, a spectrum is formed having single lines or band lines at definite positions and the lines have definite frequencies also. The line spectra are also formed by atoms and are called atomic spectra. The band spectra are actually a collection of many lines formed by a molecule and is also called a molecular spectrum. Line spectra are characteristic properties of elements.

### Define the term Solution / What is Solution in Chemistry?

Solution : Whenever two or more than two non-reacting substances are mixed, the resulting system is called a mixture. A solution is a homogeneous mixture of two or more substances in their molecular level.

### Draw the molecular structure of XeF2, XeF4, XeF6.

Xenon forms three stable fluorides, XeF2, XeF4, XeF6. The molecular structure of XeF2 is linear, that of XeF4 is square planar and that of XeF6 is pentagonal pyramidal. They are given in the following figure,

### What are inert gases ? why are they so called ?

Inert gases : The elements of the zero group of the periodic table are known as inert gases. They are also known as noble or rare gases. The inert gases are six in numbers. They are,

### Write a short note on Chemical Kinetics.

Chemical kinetics : The branch of physical chemistry which deals with the study of the speed or rate of chemical reactions and also the explanation of their mechanism is called chemical kinetics.

### What do you mean by conjugate acid-base pair ?

Conjugate acid-base : The base formed by the donation of a single proton by an acid is called the conjugate base of the acid. Similarly, the acid formed by the acceptation of a single proton by a base is called the conjugate acid of the base.