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The Mole, Chemical Equations, and Stoichiometry - Key Concepts

The Mole, Chemical Equations, and Stoichiometry

Key Concepts

  • Avogadro's Number and the Mole

    • Avogadro's Number: Defined as the number of particles (atoms, molecules, etc.) found in one mole of a substance. This value is approximately 6.022 imes 10^{23} particles/mole.
    • The Mole: A fundamental unit in chemistry used to express amounts of a chemical substance. 1 mole of any substance contains the same number of entities (atoms, molecules, etc.) as there are atoms in 12 grams of carbon-12.

  • Molar Mass and Percent Composition

    • Molar Mass: The mass of one mole of a substance, usually expressed in grams per mole (g/mol). The molar mass can be calculated from the atomic masses of its constituent elements found on the periodic table.
    • Percent Composition: The percentage by mass of each element in a compound, calculated using the formula:
      ext{Percent Composition of Element} = rac{ ext{Mass of Element in 1 mole of Compound}}{ ext{Molar Mass of Compound}} imes 100

  • Calculating Empirical and Molecular Formulas

    • Empirical Formula: The simplest whole-number ratio of atoms of each element in a compound. To determine the empirical formula:
    1. Convert the mass of each element to moles by using their molar masses.
    2. Divide all mole values by the smallest mole value to obtain the simplest ratio.
    • Molecular Formula: Represents the actual number of atoms of each element in a molecule. The molecular formula can be derived from the empirical formula by multiplying the subscripts by a whole number factor, found via the formula:
      ext{Molecular Formula} = n imes ext{Empirical Formula}
      where n = rac{ ext{Molar Mass of Compound}}{ ext{Empirical Formula Mass}}

  • Balancing Chemical Equations

    • Chemical Equation: A representation of a chemical reaction that shows the reactants and products with their respective amounts.
    • Balancing: The process of ensuring the number of atoms of each element is the same on both sides of the equation. This is achieved by adjusting coefficients (the numbers placed before compounds)
    • Law of Conservation of Mass: In a chemical reaction, the mass of the reactants must equal the mass of the products, emphasizing the need for balanced equations.
    • Example of a balanced equation:
      2H2 + O2
      ightarrow 2H_2O
      Here, the number of hydrogen and oxygen atoms is equal on both sides.

  • Stoichiometry

    • Stoichiometry: The calculation of reactants and products in chemical reactions based on the balanced chemical equation.
    • Limiting Reagents: The reactant that gets completely consumed in a chemical reaction, limiting the amount of product formed. To identify the limiting reagent:
    1. Calculate moles of each reactant.
    2. Use the stoichiometric coefficients from the balanced equation to determine which reagent will run out first.
    • Theoretical Yield: The maximum amount of product that can be predicted from the amounts of reactants used, calculated using stoichiometry based on the balanced equation.
    • Percent Yield: The measure of the efficiency of a reaction, defined as: ext{Percent Yield} = rac{ ext{Actual Yield}}{ ext{Theoretical Yield}} imes 100
      • The actual yield is the measured amount of product obtained from a reaction.

Chapter Reference

  • Chapter 4 begins on page 63, focusing on a detailed study of the mole, chemical equations, and stoichiometry.