Stoichiometry

Involves the mass relationships between reactants and products in a

chemical reaction.

Problem Type 1

• Given and unknown quantities are amounts in moles.

• This is a mol mol calculation.• To solve these problems you need the mole ratio = a conversion factor that relates the amounts in moles of any two substances in a chem Rxn.

Example

• Ammonia, NH3, is widely used as a fertilizer and as an ingredient in many household cleaners. How many moles of ammonia are produced when 6 mol of hydrogen gas react with an excess of nitrogen gas?

H2 + N2 NH3

Problem Type 2

• Given is in moles and unknown is expressed in grams (mass).

• This is a mol mol mass conversion calculation.

Example

• When magnesium burns in air, it combines with oxygen to form magnesium oxide according to the following equation

2Mg + O2 2MgO

What mass is grams of MgO is produced from 2 moles of Mg?

Problem Type 3

• Given is a mass in grams and unknown is in moles.

• This is a mass mol mol calculation.

Example

• Oxygen was discovered when heated mercury (II) oxide decomposed to form its constituent elements. How many moles of HgO are needed to produce 125 g of oxygen, O2?

Problem Type 4

• Given and unknown amounts are in grams (mass).

• This is a mass mol mol mass calculation.

Example

• When copper metal is added to silver nitrate in solution, silver metal and copper (II) nitrate are produced. What mass of silver is produced from 100g of Cu?