Quantitive aspects of chemical change

QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

Stoichiometric Calculations

1. Write down the balanced equation
2. Identify the substances needed
3. Convert the given information to moles
4. Determine the number of moles using the mole ratio
5. Convert back to mass, volume or concentration as needed

The mole and Avogadro’s constant
 Mole is the SI unit used to indicate amount of substance
 The amount of a substance containing as many particles as there
are atoms in 12g of carbon-12
 This number is Avogadro’s constant (NA) (6,021023)
 Number of particles = nNa

The mole and mass
 The relative atomic mass of an element is a figure comparing the
real mass of one atom of the element with 112of the mass of the
carbon-12 atom which has a mass of 12 atomic mass units
 Isotopesatoms of the same element but with different numbers of
neutrons (same atomic number, different mass number)
 Molar mass of the substancethe relative atomic mass of an
element or the relative molecular/ formula mass of a compound in
grams indicates one mole of the specific element or compound
 n=mMwhere n= number of moles, m=mass, M= molar mass

Molar volume of gases
 Avogadro’s Lawequal volumes of different gases at the same
temperature and pressure contain the same number of moles of
gas
 Molar gas volumeone mole of any gas at STP occupies a volume
of 22,4 dm3
Concentration of solutions
 c=nv where c= concentration, n= number of moles, v= volume of
solution
 Unit = moldm-3
 Standard solutiona solution of which the exact concentration is
known