Limiting Reactants in Chemical Reactions
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Questions and Answers

What is the role of the limiting reactant in a chemical reaction?

  • It determines the maximum amount of product formed. (correct)
  • It can be used to produce infinite amounts of product.
  • It is always present in larger quantities than other reactants.
  • It does not participate in the chemical reaction.

    • When calculating the excess reactant remaining after a reaction, which formula is used?

  • Excess moles = moles (reacted) - given moles
  • Excess mass = mass (reacted) + given mass
  • Excess moles = given moles + moles (reacted)
  • Excess mass = given mass - mass (reacted) (correct)

    • In the reaction 2Al + Fe2O3 → Al2O3 + 2Fe, if Aluminum (Al) is the limiting reactant, what can be determined about Iron(III) oxide (Fe2O3)?

  • It will be present in excess after the reaction. (correct)
  • It has no effect on the production of Al2O3.
  • It is the limiting reactant.
  • It will fully react with Aluminum to produce Al2O3.

    • What mass of Al2O3 is produced when 124 g of Al is reacted with 601 g of Fe2O3?

    <p>Both options A and B.</p> Signup and view all the answers

    What is true about the excess reactant after a reaction has occurred?

    <p>It is present in quantities greater than necessary.</p> Signup and view all the answers

    In the reaction between aluminum and iron(III) oxide, which reagent is identified as the limiting reagent?

    <p>Al</p> Signup and view all the answers

    What is the theoretical yield of aluminum oxide (Al2O3) produced when starting with 124 g of aluminum?

    <p>234 g</p> Signup and view all the answers

    If 601 g of Fe2O3 is provided in the reaction with aluminum, what is the excess mass of Fe2O3 after the reaction?

    <p>234 g</p> Signup and view all the answers

    What formula is used to calculate percent yield?

    <p>Actual Yield / Theoretical Yield x 100</p> Signup and view all the answers

    Which of the following statements about theoretical yield and actual yield is true?

    <p>Theoretical yield is the maximum amount of product expected.</p> Signup and view all the answers

    In the reaction of manganese dioxide with hydrochloric acid, if 0.86 mol of MnO2 is used, how would you determine the excess reagent?

    <p>Compare moles of MnO2 with HCl based on the balanced equation.</p> Signup and view all the answers

    When combining reactants, what step is crucial to find out which is the limiting reagent?

    <p>Divide the number of moles of each reactant by the coefficients in the balanced equation.</p> Signup and view all the answers

    If 48.2 g of HCl reacts with 0.86 mol of MnO2, what reagent will likely be used up first?

    <p>HCl</p> Signup and view all the answers

    Using the information provided, if 18.6 g of Cl2 is collected from the reaction, what does this represent?

    <p>Actual yield</p> Signup and view all the answers

    In the balanced equation 2C2H6 + 7O2 → 4CO2 + 6H2O, how many atoms of oxygen are present on the reactants side?

    <p>14</p> Signup and view all the answers

    What is the molar mass of methanol (CH3OH) used in the combustion reaction?

    <p>32.0 g</p> Signup and view all the answers

    What is the empirical formula of a compound with 0.108 mol of nitrogen and 0.217 mol of oxygen?

    <p>NO2</p> Signup and view all the answers

    Which reagent is described as the limiting reagent in the reaction 2NO + O2 → 2NO2?

    <p>NO</p> Signup and view all the answers

    When balancing the equation C2H6 + O2 -> CO2 + H2O, which coefficient should be used for H2O in the balanced equation?

    <p>3</p> Signup and view all the answers

    What is the first step in calculating the quantity of a product in a chemical reaction?

    <p>Write a balanced chemical equation</p> Signup and view all the answers

    In a chemical reaction, if 48.6 grams of magnesium reacts with 32.0 grams of oxygen to produce 80.6 grams of magnesium oxide, what is the mass change of the reactants?

    <p>0 grams</p> Signup and view all the answers

    Which statement correctly describes the process of determining the molecular formula from the empirical formula NO2?

    <p>The molecular formula is found by multiplying the empirical formula's subscripts by a whole number.</p> Signup and view all the answers

    How do you calculate the mass of water produced from 209 g of methanol in combustion?

    <p>Convert grams of methanol to moles, then to moles of water, and back to grams</p> Signup and view all the answers

    If a certain reaction has an excess reagent, what does this imply about the other reactants?

    <p>They are completely consumed</p> Signup and view all the answers

    In the reaction of ethane with oxygen, which order of balancing should be followed as indicated in the balancing procedure?

    <p>Balance the element appearing in only one reactant and product first.</p> Signup and view all the answers

    Which term refers to the reactant that is not completely consumed in a chemical reaction?

    <p>Excess reactant</p> Signup and view all the answers

    In a balanced chemical equation, what do the stoichiometric coefficients indicate?

    <p>The ratio of moles of each substance involved</p> Signup and view all the answers

    When balancing the equation C2H6 + O2 → CO2 + H2O, what is the next step after multiplying O2 by 7?

    <p>Ensure the same number of each type of atom on both sides</p> Signup and view all the answers

    What is indicated by the total number of moles of reactants compared to the total number of moles of products in a balanced chemical equation?

    <p>The law of conservation of mass is upheld.</p> Signup and view all the answers

    What must not be changed when balancing chemical equations?

    <p>The subscripts</p> Signup and view all the answers

    In a reaction producing two products, if one product has a higher stoichiometric coefficient than the other, what can be inferred about the limiting reactant?

    <p>It is completely consumed when the reaction goes to completion.</p> Signup and view all the answers

    What is the empirical molar mass of the compound NO2?

    <p>46.01 g</p> Signup and view all the answers

    Study Notes

    Mass Relationships in Chemical Reactions

    • This chapter explores the quantitative relationships between substances in chemical reactions.
    • It bridges the micro world (atoms and molecules) with the macro world (moles).
    • Atomic mass is the mass of an atom in atomic mass units (amu).
    • Mass number is equal to atomic mass in amu.

    Atomic Mass or Atomic Weight

    • Atomic mass is the mass of an atom in atomic mass units (amu).
    • Example: 1H = 1.001 amu, 12C = 12.00 amu, 16O = 16.00 amu.
    • 1 amu is exactly 1/12 the mass of a 12C atom.

    Average Atomic Mass

    • The average atomic mass, is a weighed average of all the isotopes present in a sample.
    • Isotopes have differing numbers of neutrons, but the same number of protons and electrons.
    • This average considers the natural abundance of each isotope.

    Avogadro's Number

    • One mole (mol) of a substance contains Avogadro's number of elementary units.
    • Avogadro's number (Nₐ) is 6.022 x 10²³.
    • One mole of 12C atoms is exactly 12 grams.

    Molar Mass

    • The molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol).
    • It is numerically equal to the atomic or molecular/formula mass in amu.

    Molecular Mass

    • The molecular mass is the sum of the atomic masses (in amu) of all atoms in a molecule.
    • Example: SO₂ has a molecular mass of 64.07 amu (32.07 + 2 * 16.00).
    • Molecular mass (amu) = molar mass (grams).

    Formula Mass

    • The formula mass is the sum of the atomic masses in a formula unit of an ionic compound.
    • Example: NaCl has a formula mass of 58.44 amu (22.99 + 35.45).
    • Formula mass (amu) = molar mass (grams).

    Percent Composition of Compounds

    • This calculates the percentage of each element by mass within a compound.
    • Percent composition = (n x molar mass of element / molar mass of compound) x 100%
    • Where n is the number of moles of the element in one mole of the compound.

    Determination of Empirical Formula

    • A method to determine the simplest whole-number ratio of atoms in a compound.
    • Steps involve converting percentages (if given) to masses, then mass to moles, then dividing by the smallest number of moles derived.

    Determination of Molecular Formula

    • This formula describes the actual number of atoms of each element.
    • It's based on the empirical formula and the compound's molar mass.
    • x = molar mass / empirical molar mass

    Limiting Reactants

    • A limiting reactant is a reactant that is completely consumed during a chemical reaction, limiting the amount of product that can be formed.
    • An excess reactant remains after the reaction; there's more of it than required.
    • Method one determines the amount of product formed from each reactant to pinpoint the limiting reagent.
    • Method two compares the mole ratios of reactants to locate the limiting reactant.

    Reaction Yield

    • Theoretical yield is the maximum amount of product that can be produced.
    • Actual yield is the measured amount of product produced.
    • Percentage yield = (actual yield/ theoretical yield) x 100 %

    Chemical Reactions and Equations

    • Chemical reactions involve a transformation of substances into other substances.
    • A chemical equation uses symbols to represent these transformations.
    • The equation's coefficients represent the mole ratios.

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    Mass Relationships in Chemical Reactions PDF

    Description

    This quiz explores the concept of limiting reactants in chemical reactions, focusing on calculations involving excess reactants, theoretical yields, and percent yields. Test your understanding of these fundamental principles with practical examples and problem-solving scenarios.

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