Stoichiometry and Chemical Equations

Balancing Chemical Equations

Balancing chemical equations is essential to ensure the conservation of mass and atoms in a chemical reaction. The process involves adjusting coefficients to have equal numbers of each atom on both sides of the equation.

• Step 1: Balance carbon (C) and hydrogen (H) atoms first.

• Step 2: Balance oxygen (O) atoms last.

Example:

• Unbalanced:

• Balanced:

Molar Mass and Percent Composition

Calculating Molar Mass

The molar mass of a compound is the sum of the atomic masses of all atoms in its formula, expressed in grams per mole (g/mol).

• Example: For :

  • C: g/mol

  • H: g/mol

  • N: g/mol

  • O: g/mol

  • Total: g/mol

Calculating Moles

Moles are calculated by dividing the mass of a substance by its molar mass.

• Example:

Percent Composition

Percent composition by mass of an element in a compound is calculated as:

Molecules and Atoms Calculations

Avogadro's Number

Avogadro's number () is used to convert between moles and number of molecules or atoms.

• Number of molecules:

• Example:

Atoms in a Compound

• To find the number of atoms of a specific element in a compound, multiply the number of molecules by the number of that atom per molecule.

• Example:

Limiting Reactant and Percent Yield

Limiting Reactant

The limiting reactant is the reactant that is completely consumed first, limiting the amount of product formed.

• Calculate moles of each reactant.

• Compare mole ratios using the balanced equation.

• Example:

  • Limiting reactant:

Theoretical and Percent Yield

• Theoretical yield: Maximum amount of product possible from limiting reactant.

• Percent yield:

• Example:

Electrolytes and Acids

Classification of Electrolytes

Electrolytes are substances that conduct electricity when dissolved in water. They are classified as strong or weak based on their degree of ionization.

• Strong electrolytes: Completely ionize in solution (e.g., HBr).

• Weak electrolytes: Partially ionize in solution (e.g., acetic acid).

Classification of Acids

• Strong acids: Ionize completely (e.g., HBr).

• Weak acids: Ionize partially (e.g., acetic acid, ).

Precipitation and Net Ionic Equations

Precipitation Reactions

Precipitation occurs when two aqueous solutions react to form an insoluble solid (precipitate).

• Example:

• Net ionic equation:

Neutralization Reactions

Neutralization is the reaction of an acid and a base to form water and a salt.

• Example:

• Net ionic equation:

Oxidation Numbers and Redox Reactions

Assigning Oxidation Numbers

Oxidation numbers are assigned to atoms to track electron transfer in reactions.

• H in acids: +1

• O: -2 (except in peroxides)

• Sum of oxidation numbers in a neutral compound is zero.

Redox Reactions

Redox (oxidation-reduction) reactions involve the transfer of electrons between species.

• Example:

• Net ionic equation:

Solutions and Dilutions

Calculating Molarity

Molarity (M) is the concentration of a solution, defined as moles of solute per liter of solution.

• Example:

Dilution Calculations

To dilute a solution, use the formula .

• Example: To dilute NaCl to three times its volume:

Summary Table: Electrolyte and Acid Classification

Additional info: These notes cover foundational topics in General Chemistry, including stoichiometry, solution chemistry, acid-base and redox reactions, and classification of electrolytes. All calculations and equations are based on standard chemical principles and conventions.