Overview
This lecture covers the kinetic molecular theory of gases, gas properties, the major gas laws (Boyle's, Charles', Avogadro's, combined, and ideal gas law), pressure units and conversions, and Dalton’s Law of Partial Pressures, including example calculations.
Kinetic Molecular Theory (KMT)
- KMT is a model describing gas behavior based on molecules in random, constant motion.
- Four main tenets:
- Gas particles move randomly and constantly (like blindfolded bumper cars).
- No attractive or repulsive forces exist between particles.
- The space between particles is much greater than their size; particle volume is negligible.
- Particle speed (and kinetic energy) increases with temperature.
Properties of Gases
- Gases are compressible due to large spaces between particles.
- Gases assume the shape and volume of their container.
- Gases have much lower densities than solids and liquids.
Gas Pressure and Units
- Gas pressure results from collisions of particles with surfaces.
- Common pressure units: atmospheres (atm), millimeters of mercury (mm Hg), torr, and pascals (Pa).
- Room pressure ≈ 1 atm = 760 mm Hg.
Manipulating Gas Pressure
- Increasing temperature increases pressure (faster/harder collisions).
- Decreasing volume increases pressure (more frequent collisions).
- Increasing moles (n) increases pressure (more particles = more collisions).
Boyle’s Law (Pressure-Volume Relationship)
- For constant temperature and moles: (P_1V_1 = P_2V_2).
- Pressure and volume are inversely related; as one increases, the other decreases.
Charles’ Law (Volume-Temperature Relationship)
- For constant pressure and moles: (\frac{V_1}{T_1} = \frac{V_2}{T_2}).
- Volume and temperature (in Kelvin) are directly related; both increase or decrease together.
Combined Gas Law
- For constant moles: (\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}).
- Allows prediction when more than two variables change.
Avogadro’s Law (Moles-Volume Relationship)
- For constant pressure and temperature: (\frac{V_1}{n_1} = \frac{V_2}{n_2}).
- Volume and number of moles are directly related.
Ideal Gas Law
- Used when conditions are constant: (PV = nRT).
- R = 0.0821 L·atm/(mol·K); use atm for pressure, L for volume, mol for amount, K for temperature.
Real vs. Ideal Gases
- Ideal gas behavior: high temperature, low pressure (particles far apart, little interaction).
- Non-ideal behavior: low temperature, high pressure (particles close, intermolecular interactions).
Dalton’s Law of Partial Pressures
- Total pressure equals the sum of partial pressures of all gases present.
- Each gas contributes pressure proportional to its mole fraction in the mixture.
Key Terms & Definitions
- Kinetic Molecular Theory — a model that explains gas behavior via particle motion.
- Pressure (P) — force per unit area from particle collisions.
- Volume (V) — the space the gas occupies.
- Moles (n) — the amount of gas particles.
- Temperature (T) — measure of average kinetic energy (in Kelvin).
- Partial Pressure — the pressure exerted by one gas in a mixture.
- Ideal Gas Constant (R) — proportionality constant in the ideal gas law.
Action Items / Next Steps
- Review Table 11.1 (common gas pressure units and conversions).
- Practice solving gas law problems using provided equations.
- Know how to convert temperature to Kelvin for gas calculations.
- Be prepared to use and interpret each gas law formula on exams.