Other Conversions:

·         Volume @ STP can be found using the conversion factor 22.4L/1mol

Ex.  If 6.0g of KCLO3 decompose according to the reaction below, what volume of O2 (@ STP) is produced?

1.      Balanced Eq’n: 2KClO3 à 2KCL + 3O2

2.      6.0g x 1mol/122.6g x 3/2 x 22.4L/1mol

= 1.6L

·         Heat can be included as a separate term in chemical reactions (enthalpy)…

·         Things to keep in mind when solving these eq’ns are that rxns that release heat are exothermic and rxns that absorb heat are endothermic. 

Ex.  Find the amount of heat released when 2.0mol of H2 are consumed accordingly to the reaction…

1.      Balanced Eq’n:  N2 +3H2 à 2NH3 + 46.2 kJ

2.      2.0mol x 46.2/3

=77kJ

Ex.  To find the amount of heat released when 675g of ammonia for according to the reaction below…

1.      Balanced Eq’n:  N2 + 3H2 à 2NH3 + 46.2kJ

2.      675g x 1mol/17g x 46.2/2

= 46.2kJ

Mole to Mass & Mass to Mole Conversions

Moles to Mass conversions…

·         Give you an amount of Moles and ask you to determine the mass.

·         Converting Moles – Mass only requires one additional step. 

Ex.  When silver reacts with 3.45 moles of zinc phosphate what mass of silver phosphate would be produced?

1.      Balanced Eq’n:  6Ag + Zn3(PO4)2 à 3Zn + 2Ag3PO4

2.      3.45mol x 2/1 x 418.7g/1mol

= 2889.03 ~ 2.89 x 10^3g

Ex.  You are given 4.00g of methane and are expected to burn it in order to initiate a chemical reaction.  How many moles of water vapour would be produced? 

1.      Balanced Eq’n:  CH4 + 2O2 à 2H2O + CO2

2.      4.00g x 1mol/16g x 2/1

= 0.500 mol

Mass-to-Mass conversions…

·         Involve one additional step to the “Moles to Mass” conversions

Ex.  When aluminum reacts with Iron (III) oxide to produce solid iron and aluminum oxide, what is the mass of aluminum oxide produced along with 19.55g of iron?

1.      Balanced Eq’n:  2Al + Fe2O3 à 2Fe + Al2O3

2.      19.55 x 1mol/55.8g x ½ x 102g/1mol

= 17.87g

·         To achieve the mass of aluminum oxide as shown above, we simply take its amu and multiply it by the final amount of moles. 

Ex.  Sodium iodide reacts with lead (II0 nitrate to produce sodium nitrate and lead (II) iodide.  What mass of lead (II) nitrate will be required to produce 150g of sodium nitrate?

1.      Balanced Eq’n:  2NaI + Pb(NO3)2 à NaNO3 + PbI2

2.      150g x 1mol/85g x ½ x 331.2/1mol

= 292g