Chemistry Definition

Definition

Chemistry : It is the branch of science that studies the composition, properties and interaction of matter. The aspects of matter can be best described and understood in terms of basic constituents of matter i.e. atoms and molecules.


MATTER : Anything which has mass and occupies space is called matter. e.g. Book, pen, water, air, etc.

MIXTURE : A mixture is a substance which has two or more substances mixed in any ratio.

HOMOGENEOUS MIXTURE : In this, all the components mix completely with each other and its composition is uniform throughout. e.g. sugar solution, air etc.

HETEROGENEOUS MIXTURE : Its composition is not uniform throughout. Sometimes different components of mixture can be seen. e.g. mixture of salt and sugar, mixture of grains and pulse.

PURE SUBSTANCES : They have fixed composition. e.g. Glucose contains `C`, `H` and `O` in a fixed ratio and gold, silver etc.

ELEMENTS : It consists of only one type of particles. i.e. one type of atoms or molecules. e.g. `Na`, `Cu`, `Ag`, `H`, `O` etc.

COMPOUNDS : These are obtained by combining two or more atoms of different elements. e.g. water (`H_2O`) ammonia (`NH_3`) etc

PHYSICAL PROPERTIES : These are the properties in which identity or composition of the substance remain same. e.g. colour, odour, melting point, boiling point, density etc.

CHEMICAL PROPERTIES : These are the properties in which there is a change in identity or composition of the substance. e.g. acidity or basicity, combustibility etc.

SCIENTIFIC NOTATION : Since atoms and molecules have extremely low mass and are large in numbers. So, for dealing with such a large and small number scientific notation is used. It is also called exponential notation. so we write it in scientific notation:
`N xx 10^n`

PRECISION : It is the closeness of various measurements for the same quantity.

ACCURACY : It is the agreement of a particular value to the true value of the result

DIMENSIONAL ANALYSIS : For converting units from one system to other a method was accomplished which is called `text(factor label method)` or `text(unit factor method)` or `text(dimensional analysis)`.

LAW OF CONSERVATION OF MASS : Matter can neither be created nor destroyed.

LAW OF DEFINITE PROPORTIONS : A given compound always contains exactly the same proportion of element by weight.

LAW OF MULTIPLE PROPORTIONS : If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers. This law was given by Dalton in 1803.

GAY LUSSAC'S LAW OF GASEOUS VOLUMES : When gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at
same temperature and pressure.

AVOGADRO'S LAW : Equal volumes of gases at the same temperature and pressure should contain equal number of molecules.

DALTON'S ATOMIC THEORY : (i) Matter consists of indivisible atoms.

(ii) All the atoms of a givens elements have identical properties including identical mass.

(iii) When atoms of different elements combine in a fixed ratio, compounds are formed.

(iv) Chemical reactions involve reorganization of atoms. These are neither created nor destroyed in a chemical reaction.


ATOMIC MASS : The atomic mass of atom is given relative to `C-12`. `text()12^C` is assigned a mass of exactly `12` atomic mass unit (amu) and masses of all other are given relative to this standard.

AVERAGE ATOMIC MASS : The average atomic mass of an element is the sum of atomic masses of its isotopes, each multiplied by its natural abundance

MOLECULAR MASS : It is the sum of atomic masses of the elements present in a molecule

FORMULA MASS : It is the sum of atomic masses of all the atoms in a formula unit of ionic compound .

MOLE : One mole is the amount of a substance that contains as many particle or entities (Atoms, molecules, ions or other
particles) as there are atoms in exactly `12 g` (or `0.012kg`) of the `text()^12C` isotope.

MOLAR MASS : The mass of one mole of a substance in grams is called its molar mass.

PERCENTAGE COMPOSITION : Percentage composition gives the idea about the purity of a given sample by analyzing the given data.

Mass `%` of an element `= text(mass of that element in the compound)/text(molar mass of the compound)`

EMPIRICAL FORMULA : It represents the simplest whole number ratio of various atoms presents in a compound.

MOLECULAR FORMULA : It is the exact number of different types of atoms present in molecule of a compound.

LIMITING REAGENT : When one reactant is in excess over the other then the reactant which is present in the lesser amount gets consumed and no reaction takes place whatever be the amount of the other reactant presents. Therefore the reactant which gets consumed limits the amount of product and is called the limiting reagents.


MASS PERCENT : `=text( Mass of solute)/text(mass of solution)xx100`

MOLE FRACTION : If a substance `A` is dissolved in substance `B` and their no. of moles are `n_A` and `n_B` respectively, then

Mole fraction of `A` `= text(No. of moles of A)/text(No. of moles of solution)`

Mole fraction of `B` `= text(No. of moles of A)/text(No. of moles of solution)`

MOLARITY : It is the number of moles of the solution in `1` L of the solution. It is denoted by `M`.

(`M`) `= text(No. of moles of solute)/text(volume of solutions in liters)`

MOLALITY : It is the number of moles of the solution in 1 kg of the solvent. It is denoted by `m`.

(`m`) `= text(No. of moles of solute)/text(Mass of solvent in kg)`



Formula

(1). Density : `d = m/V`

Where `d =` density

`m =` mass

`V =` volume

(2). Temperature : `text()^oF = 9/5 (text()^oC) + 32`

(3). Scientific Notation : `N xx 10^n`

where `n =` an exponent having positive or negative values.

`N =` any number between `1.000-9.999` is called digit term.

(4). Percentage Composition : Mass `%` of an element `= text(mass of that element in the compound)/text(molar mass of the compound)`


(5). Mass percent `=text( Mass of solute)/text(mass of solution)xx100`

(6). Mole fraction of `A` `= text(No. of moles of A)/text(No. of moles of solution)`

(7). Molarity (`M`) `= text(No. of moles of solute)/text(volume of solutions in liters)`

(8). Molality(`m`) `= text(No. of moles of solute)/text(Mass of solvent in kg)`

 
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