lecture recording on 21 February 2025 at 09.54.27 AM

Equality of Variables

• If a = b = c, then a equals c.

  • Importance of recognizing that a, b, and c are equivalent.

  • No priority in order; all variables are equal.

Mole Concept

• Three equivalencies:

  • 1 mole is 6.02 x 10^23 particles (atoms, molecules, etc.).

  • The mass in grams is equal to the mass number on the periodic table.

  • Example:

    • 1 mole of Carbon = 6.02 x 10^23 Carbon atoms = 12 grams.

Carbon as an Example

• Carbon atoms have a mass number of 12 on the periodic table.

• Distinction between:

  • Atom: single unit (e.g., Carbon atom).

  • Molecule: combination of atoms (e.g., H2O).

  • Formula unit: ionic compound (e.g., NaCl).

Why Use Moles?

• Moles simplify conversion between particles and grams:

  • Moles allow for practical measurements in chemistry; one cannot weigh out a dozen atoms.

  • Utility of the mole is akin to that of a dozen in everyday counting.

Application of Moles in Stoichiometry

• Convert grams to moles for chemical reactions.

  • Example: 400 grams of gold.

  • Use the mass number of an element to convert (1 mole Au = 197 grams).

Unit Conversion Steps

1. Identify the given quantity (e.g., mass of gold).

2. Set up the conversion with units (grams to moles).

   • If given: weight in grams, need to find moles, set up as:

     • 400 grams (Au) × (1 mol Au / 197 g Au).

3. Perform the calculations:

   • Clear units to leave only moles.

Example Problem: CO2

• To find moles in 28 grams of CO2:

  • Calculate the molar mass:

    • C = 12 g/mol

    • O = 16 g/mol, but there are 2 O atoms in CO2, so 16g/mol × 2 = 32 g/mol.

    • Total = 12 + 32 = 44 g/mol.

  • Convert grams to moles:

    • 28 g CO2 × (1 mol CO2 / 44 g CO2).

Class Structure and Upcoming Focus

• Office hours for further assistance.

• Plan for applying the concepts in problem-solving and practice.

• Importance of reviewing prior lessons to succeed in upcoming assessments.