Lecture Notes: Dalton's Law

Introduction to Dalton's Law

• Focuses on ideal gases and their behavior in mixtures.
• Traditionally, gas laws pertain to individual gas samples.
• Dalton's Law is crucial for understanding gaseous mixtures.

Key Concepts

Partial Pressure

• The pressure each gas exerts in a mixture is its partial pressure.
• Total pressure in a vessel is the sum of the partial pressures of each gas.
• Assumes no chemical reactions between gases.

Total Pressure Calculation

• Total pressure = Sum of partial pressures.
• Pressure: Force exerted by gas particles striking container sides.
• In ideal gases, identities of gases are irrelevant to pressure.

Partial Pressure and Mole Fraction

• Mole Fraction: Ratio of moles of a substance to total moles in mixture.
• Partial pressure = Mole fraction × Total pressure.
  • Example: 0.25 mole fraction, 800 torr total pressure → Partial pressure = 200 torr.
• At molecular level, relates to collisions of particles with container walls.

Practical Application: Atmospheric Sample

• Atmosphere at sea level contains nitrogen, oxygen, argon, etc.
• Total pressure = Atmospheric pressure (1 atm).
• Dalton's Law: Sum of partial pressures = Total pressure.
• Calculation:
  • Convert gas percentages to mole fractions.
  • Multiply mole fractions by total pressure for partial pressures.
  • Partial pressures should sum to 1 atm, mimicking percentage sums to 100%.

Advanced Calculations

• Use with other gas laws for complex scenarios.
• Example:
  • Known moles of gases in a vessel of known volume and temperature.
  • Use Ideal Gas Law to find total pressure.
  • Calculate mole fractions and deduce partial pressures.

Summary

• Dalton's Law is intuitive and essential for calculations involving gas mixtures.
• Useful for determining partial pressures in various conditions.

Conclusion

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