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.