Moles, excess and limiting reagents - Stoichiometry

Moles, excess and limiting reagents

Lessons

Notes:
In this lesson, we will learn:
• To fully understand the language used to describe chemical reactions.
• To identify by calculation the limiting reagents in a given chemical reaction.
• To calculate quantities of excess reagents.

Notes:

• For a chemical reaction to happen, all of the reactants must be present and available to react. If any one reactant is not present, the reaction will not happen.

• Chemical reactions proceed until one of the chemical reactants runs out. When one of these chemicals runs out, the reaction stops and no more products can be made.

• The chemical that you have the least amount of, or that runs out first is called the limiting reagent because its running out limits the reaction from happening any longer.

• All the other reagents (reactants) involved that are not limiting reagents are excess reagents, or are “in excess”. We call it this because when the reaction stops there will still be some of these reagents left over, unreacted and unable to react.

• To find out the limiting reagent, you need to find the amount of product that can be made, with respect to each reactant involved. The reactant that would produce the smallest amount of product is the limiting reagent.

• To find the mass of excess reagent, find the amount of the excess reagent that reacts based on the amount of limiting reagent. Then, subtract that from the total amount of excess reagent available.

• Knowing your limiting reagent is important because a limit on the amount of reagents available puts a limit on the amount of products formed too!

  • Intro Lesson
  • 1.
    Find the limiting reagent in a chemical reaction with known quantities.
    Study the reaction: 2H2+_2 + O2_2 →2H2_2 O
  • 2.
    Find the limiting reagent in a chemical reaction with known quantities.
    Study the reaction: 2C6_6H14+_{14} + 19O2_2 →12CO2+_2 + 14H2_2O
  • 3.
    Find the limiting reagent in a chemical reaction with known quantities.
    500 g of Fe2_2O3_3 is reacted with 750 g of C in the reaction: 2Fe2_2O3(s)+_{3\;(s)} + 3C(s)_{\;(s)} →4Fe(s)+_{\;(s)} + 3CO2(g)_{2\;(g)}
  • 4.
    Find the limiting reagent in a chemical reaction with known quantities.
    45 g of Ca3_3(PO4_4)2_2 is reacted with 36 g C and 85 g SiO2_2 according to the reaction:
    2Ca3_3(PO4_4)2+_2 + 6SiO2+_2 + 10C→P4+_4 + 6CaSiO3+_3 + 10CO
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Moles, excess and limiting reagents

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