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Understanding Chemical Formulae and Reactions

May 4, 2025

Lecture Notes on Chemical Formulae, Equations, and Calculations

Overview

  • Introduction to chemical formulae, equations, and calculations as foundational concepts in chemistry.

Chemical Formulae

  • Definition: A chemical formula represents the types and numbers of atoms in a molecule.
  • Types of Chemical Formulae:
    • Empirical Formula: The simplest integer ratio of elements in a compound.
    • Molecular Formula: The actual number of atoms of each element in a molecule.
      • Molecular formula = n × empirical formula (where n is an integer)
    • Structural Formula: Shows the arrangement of atoms in a molecule.

Writing Chemical Equations

  • Components of a Chemical Equation:
    • Reactants: Substances that start a chemical reaction.
    • Products: Substances that are produced in the reaction.
    • Arrow (→) indicates the direction of the reaction.
  • Balancing Chemical Equations:
    • Law of Conservation of Mass: Matter is neither created nor destroyed.
    • Make sure the number of atoms of each element is the same on both sides.
    • Use coefficients to balance the equation, not subscripts.

Types of Reactions

  • Synthesis Reaction: Two or more simple substances combine to form a more complex substance.
  • Decomposition Reaction: A single compound breaks down into two or more simpler substances.
  • Single Replacement Reaction: One element replaces a similar element in a compound.
  • Double Replacement Reaction: The ions of two compounds exchange places in an aqueous solution to form two new compounds.

Stoichiometry

  • Definition: The part of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction.
  • Mole Concept: Relating molar mass and Avogadro's number.
  • Calculating Moles:
    • Use molar mass to convert between grams and moles.
    • Use Avogadro's number for mole to particle conversions.

Calculations Involving Chemical Reactions

  • Mole-to-Mole Conversions: Using balanced equations to convert between moles of reactants and products.
  • Mass-to-Mass Conversions: Converting mass of a substance to moles and then using stoichiometry to find mass of another substance.
  • Limiting Reactant: The reactant that is completely consumed in the reaction, limiting the amount of product formed.
  • Excess Reactant: The reactant that remains after the reaction is complete.

Conclusion

  • Mastery of chemical formulae and equations enables understanding of chemical reactions and stoichiometry.
  • Practice balancing equations and performing stoichiometric calculations for proficiency.