This document discusses key concepts related to stoichiometry including: - The mole, molar mass, and Avogadro's number are defined. Molar mass is the mass of one mole of a substance and is measured in g/mol. - Atomic mass is calculated using the ratio of isotopes multiplied by their individual masses. Molar/molecular mass has the same value as atomic mass but is measured in g/mol rather than atomic mass units. - Examples are given for calculating the molar mass of compounds like CO2, H2O, and relating mass, moles, and molar mass. - Standard temperature and pressure, stoichiometry, and dimensional analysis are also defined

1. S e c t i o n t h r e e
B y :
Y o u s s ef B e r b ar

3.  Mole : 6.022 x 10^23 units, the number equal to the
number of carbon atoms in exactly 12 g of pure C 12
 Molar mass : the mass of one mole of a pure
substance.
 Avogadro no : 6.022 x 10^23

4. How to calculate :
 How to know atomic mass ?! If we have a element
that has 2 isotopes and we want to calculate the
atomic mass we follow the following rule :
Ratio of isotope one * its mass + ratio of isotope 2 *
its mass = no its unit is Amu , also it is written
under the element symbol in the periodic table
 Molar mass = Molecular mass = atomic mass in its
magnitude

5. What is the difference between molar
, molecular and atomic mass
 Both of them are equal in magnitude but the unit of
atomic mass is Amu and the unit of molar and
molecular mass is g / mole
 Another example what is the molar mass of co2 : 12 g /
mole
 calculate the molecular mass of water (H2O) (1.01 amu
+ 1.01 amu + 16.00 amu) = 18.02 Amu or 18.02 g / mole
 Molar mass of element is no. g / mole . What means ?
Molar mass = mass / Avogadro no ( no of moles )
No of moles = mass / molar mass

6. Some definitions
 standard temperature and pressure (STP):standard
temperature is 273.15 kelvins and standard pressure is
760 mm Hg ( 1 atm).
 Stoichiometry : the study of the relationships (mass-
mole-volume) among substances involved in chemical
reactions.
 dimensional analysis : a name for “equivalent
measures.” A method for solving problems that
involves canceling units.

7.  The equation also shows that 2 mol C8H18
react with 25 mol O2 to form 16 mol CO2and 18
mol H2O.
 No of mole = mass / molar mass
 Density = mass / volume

8. Problem one

9. Solution of problem one
 Mole ratio =
 We have 312 moles of ammonia so ,

10. Problem two

11. Solution of problem two

12. Problem Three

13. Solution of problem Three

14. Problem four

15. Solution of problem four

20. Thanks for listening
Youssef Berbar