Overview
This lecture introduces the concept of the mole in chemistry, explaining its definition, significance, and various ways to calculate moles for quantitative problem-solving in chemical reactions.
What is a Mole?
- A mole is the SI unit for the amount of substance in chemistry.
- One mole equals 6.022 × 10²³ particles (atoms, molecules, or ions).
- 6.022 × 10²³ is called Avogadro’s number or Avogadro’s constant.
- Chemists use moles because counting individual atoms is impractical.
- The mole is analogous to using "dozen" for 12; "one mole" means 6.022 × 10²³ particles.
- The definition: one mole is the amount of substance containing as many particles as 12 grams of carbon-12 atoms.
Properties of the Mole
- One mole of any substance contains 6.022 × 10²³ representative particles, regardless of identity.
- Avogadro’s number is always used to relate moles to number of particles.
- The mole concept enables chemists to relate masses of substances to numbers of particles for calculations.
Calculating Moles
- Use ( n = \frac{m}{M} ) if given mass (m) and molar mass (M).
- Use ( n = c \times V ) if given concentration (c) and volume (V) of solution.
- Use ( n = \frac{V}{V_m} ) for gases at standard temperature and pressure (STP), where ( V_m = 22.4 ) dm³.
- Use ( n = \frac{N}{N_A} ) if given number of particles (N); ( N_A ) is Avogadro’s number.
- "n" represents the number of moles in all formulas.
Why Use Moles in Chemical Reactions?
- Chemists use moles to calculate amounts of reactants and products in reactions.
- Balanced chemical equations indicate moles of reactants/products using coefficients.
- To convert mass of a substance to moles, then use mole ratios to relate substances.
- Mole ratios help determine how much product forms or reactant is needed.
Key Terms & Definitions
- Mole (mol) — SI unit for amount of substance; equals 6.022 × 10²³ particles.
- Avogadro’s number (N_A) — 6.022 × 10²³, the number of particles per mole.
- Molar mass (M) — Mass in grams of one mole of substance.
- Concentration (c) — Amount of solute per volume of solution, in mol/dm³.
- STP — Standard Temperature and Pressure, conditions used for gas volume calculations.
- Mole Ratio — The ratio of moles of reactants/products from a balanced equation.
Action Items / Next Steps
- Review the formulas for calculating moles based on different information given.
- Watch videos on stoichiometry, mole calculations, and mole ratios for detailed examples.
- Practice converting between mass and moles, and using mole ratios in balanced equations.