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Limiting Reactants: Flashcards

Revise limiting and excess reactants, theoretical yield and percent yield.

9 cardsIntermediate

9 cards

  1. Question
    What is the limiting reactant?
    Answer

    The reactant that is used up first. It limits how much product can form.

  2. Question
    What is an excess reactant?
    Answer

    A reactant that is not used up completely; some is left over when the reaction stops.

  3. Question
    How do you find the limiting reactant?
    Answer

    Convert each reactant to moles, calculate how much product each could make, and pick the one that gives less product.

  4. Question
    What is the theoretical yield?
    Answer

    The maximum amount of product that can form, calculated from the limiting reactant.

  5. Question
    What is the formula for percent yield?
    Answer

    Percent yield = (actual yield ÷ theoretical yield) × 100%

  6. Question
    Is the reactant with the smaller mass always the limiting reactant?
    Answer

    No. Compare moles, using the mole ratio from the balanced equation. Mass alone tells you nothing.

  7. Question
    In 2 HX2+OX2→2 HX2O\ce{2H2 + O2 -> 2H2O}, 1.0 mol of HX2\ce{H2} mixes with 0.6 mol of OX2\ce{O2}. Which is limiting?
    Answer

    HX2\ce{H2}. It needs only 0.50 mol of OX2\ce{O2}, and 0.6 mol is available, so oxygen is in excess.

  8. Question
    Give three reasons why a percent yield is usually less than 100%.
    Answer

    The reaction may not go to completion; side reactions make other products; some product is lost during separation and purification.

  9. Question
    What does a percent yield above 100% suggest?
    Answer

    An error, for example the product is still wet or contains impurities. Extra product cannot be created.