Fun box: TEMPERATURE

DEFINITIONS

1. TEMPERATURE

   Degree of hotness or coldness of a body is called "TEMPERATURE".
   "Temperature is a measure of the intensity of heat".
   Temperature is defined as :
   "the average kinetic energy of the molecules of a body is called temperature"

SCALES OF TEMPERATURE:

   There are three scales of temperature.
   1. Celsius or centigrade scale C.
   2. Fahrenheit scale F.
   3. Kelvin or Absolute scale K.

CONVERSION

Centigrade & Kelvin

T_k = T_c + 273

Centigrade & Fahrenheit

C/5 = (F-32) /9

2. VOLUME

Volume is defined as
" The space occupied by a body is called its volume."

SYMBOL

Volume is denoted by "V

UNITS

   a) m³
   b) dm³
   c) cm³
   d) mm³
   e) Litre
   f) Milli litre

3. MASS

The quantity of matter contained in a body is called its "Mass".

SYMBOL

Mass is denoted by "m".

UNITS

   a) Kilogram
   b) Gram
   c) Milligram
   d) Microgram

4. DENSITY

Mass per unit volume of a substance is called its "Density".

FORMULA

UNIT

   a) Kg / m³
   b) gm / cm³
   c) gm /litre
   d) gm / dm³

5. MOLE

"Atomic mass or formula mass or molecular mass of a
substance expressed in grams is called MOLE".
Or
Mass of a substance contains 6.02 x 10²³ atoms or molecules or ions is called "mole"

   For example:
   1. Atomic mass of carbon = 12 a.m.u.
   therefore 12 gram of carbon = one mole of carbon.
   2. Formula mass of Nacl = 58.5 a.m.u.
   therefore 58.5 gm of Nacl = 1 mole of Nacl.
   3. Molecular mass of CO = 28 a.m.u.
   therefore 28 gm of CO = I mole of CO

FORMULA

6. AVOGADRO'S NUMBER

   One mole of any substance contains 6.02 x 10²³ atoms, molecules or ions. This particular number is    called "AVOGADRO'S NUMBER".
   It is denoted by N_A.
   For Example.
   1 mole carbon = 6.02 x 10²³ carbon atoms.
   1 mole Na+ = 6.02 x 10²³ Na+ ions.
   1 mole H₂O = 6.02 x 10²³ H₂O molecules.

7. LAW OF DEFINITE PROPORTION

STATEMENT

According to the law of definite proportion

"Every sample of pure substance always contains same elements
in fixed proportion regardless of its method of preparation"

EXPLANATION

We can obtain or prepare water by a number of methods but water obtained from any source always contain 11.11% hydrogen and 88.88% oxygen.
Similarly CO₂ can be prepared by different methods but each sample of CO₂ contains C=27.27% and O=72.72%.

8. SPECIFIC GRAVITY

Specific gravity of a substance is defined as the ratio of the mass of
substance to the mass of an equal volume of water at a particular temperature.

FORMULA

Specific gravity = mass of substance / mass of an equal volume of water

UNIT

It has no unit.

9. GRAM ATOMIC MASS

"Atomic mass of an element expressed in gram is called gram atomic mass"

   For example:
   Gram atomic mass of C=12gm.
   Gram atomic mass of H=1 gm.
   Gram atomic mass of O=16 gm.

10. GRAM MOLECULAR MASS

"Molecular mass of a molecule expressed in grams is called gram molecular mass."

   For example:
   Gram molecular mass of hydrogen gas=2 gm.
   Gram molecular mass of oxygen gas =32gm.
   Gram molecular mass of HCl = 36.5 gm

11. ELEMENT

"Element is defined as a pure substance in which all the atoms
have same chemical properties and have same atomic number"

For example:
Carbon, sodium, hydrogen, chlorine, copper, gold, iron etc.

TYPES OF ELEMENTS

   Elements can be divided into two classes.
   1. Metals.
   2. Nonmetals.

METALS

   They have shine on their surface.
   They are good conductors of electricity and heat.
   They reflect light.
   Metals are ductile.
   Metals are malleable.

EXAMPLE

Cu, Fe, Au, Na, Ca etc

NON-METALS

   They have dull surface.
   They are bad conductors of electricity and heat.
   Non-metals are non ductile.
   They cannot be drawn into sheets.
   They are brittle.
   EXAMPLE
   H₂, C, Cl₂, O₂, N₂ etc

12. VALENCY

Valency is defined as

"the combining capacity or combining power of an element with the other element"

In other words valency may be defined as:
the number of H-atoms which combine with or displace one atom of an element or a radical is called valency.

EXAMPLES

ELEMENT	VALENCY
Na, K	1
Ca, Mg	2
F, Cl	1
N	3

13. MOLECULE

The smallest unit of an element or compound, which can exist independently, is called "molecule".

14. EMPIRICAL FORMULA

"Empirical Formula is that formula which expresses the relative number
of each kind of atoms present in the molecule of a compound"
OR
"The formula of a compound which expresses the ratio in which atoms of
different elements are combined in a molecule"

Empirical formula only indicates atomic ratios but it does not indicate actual
number of atoms of different kinds present in the molecule of a compound.
Two or more compound may have same empirical formula.
Empirical formula is determined by experiment.

EXAMPLE

Empirical Formula of Benzene = CH
Empirical Formula of Glucose = CH₂O