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The Mole and Avogadro's number
CHEMISTRY - Secondary 1
In This part we will study
The mole and the volume of gas
Solid and liquid substances have definite and constant volumes, which can be measured by several methods , while the volumes of the gaseous substances equal the volumes of their containers.
Avogadro's postulate : Equal volumes of different gases contain an equal number of molecules, at the same standard temperature and pressure (STP).
STP means Standard Temperature and Pressure
Which are: 0°C temperature= 273 K 1 atm pressure = 760 mm Hg
Avogadro discovered that
at the standard conditions (at STP) :
• A mole of any gas occupies 22.4 L volume.
• A mole of any gas contains 6.02 x 1023 molecules.

The following table illustrates the relation between the number of moles of gas, its volume and its number of molecules (at STP) for different gases:

Avogadro's Law: Gas volume is directly proportional to the number of its moles when the temperature and pressure are constant.
Example (1) :
Calculate the volume which is occupied by 39.2 g of nitrogen gas (at STP). (N = 14)
Solution:

Example (2) :
Calculate the mass of a sample of nitrous gas N20 occupies 550 mL volume (at STP).
(N = 14 , O = 16)
Solution:

Example (3) :
Calculate the volume of oxygen gas (at STP) which is required for burning 1.6 g of methane gas CH4 [C=l2 ,H =l]

Best wishes to you
Mr.Ahmed Elbasha

كيمياء الصف الاول الثانوي لغات - الفصل الدراسي الاول
شرح كيمياء لغات اولي ثانوي - مستر احمد الباشا
كيمياء لغات - الصف الاول الثانوي - كيمياء اولي ثانوي الترم الاول - كيمستري اولي ثانوي الترم الاول