Daily Science pg. 82

1
Daily Science pg. 82

• You are doing the following reaction in the lab.
  You start with 108.00 g of magnesium. How many
  grams of oxygen gas do you need? How much
  magnesium oxide will you make?
• 2Mg O2 ? 2MgO

2
Limiting Reagents

• pg. 83

3
why reactions stop

• one reactant is in excess and one is limiting the
  reaction from proceeding.

4
Determining the limiting reagent

• The masses of all reactants are given
• must convert grams of each reactant into moles
• make a ratio of the moles of each
• divide the bigger number by the smaller
• compare the calculated ratio to the ratio of
  moles from the balanced equation
• If the numerator is less than the ratio from the
  reaction, it is the limiting reagent if the
  numerator is greater than the numerator in the
  ratio, it is in excess

5
Calculating the amount of product

• start with the moles of the limiting reactant and
  convert to moles of the product by using mole to
  mole ratios
• convert from moles of the product to mass of the
  product by using molar mass

6
Determining the amount of excess

• Start with the moles of the limiting reactant
• convert to moles of excess using mole to mole
  ratios
• Convert to grams using molar mass
• Subtract the calculated mass from the given mass

7
Practice

• 200.0 g of S8 reacts with 100.0 g of Cl2. Which
  is the limiting reagent? Determine the amount of
  product that will be formed and how much excess
  reactant there is.
• S8 4Cl2 ? 4S2Cl2

8
Your turn

• Determine the mass of tetraphosphorus decaoxide
  formed if 25.0 g of phosphorus and 50.0 g of
  oxygen are combined. How much of the excess
  reagent remains?
• P4 5O2 ? P4O10