Notes on Dalton's Law

Introduction to Gaseous Mixtures

• Review of ideal gases and previous laws
• Importance of understanding mixtures of different gases

Partial Pressure Concept

• Definition: Pressure exerted by an individual gas in a mixture
• Dalton's Law: Total pressure = Sum of partial pressures of individual gases
• Assumption: Gases do not react with one another

Understanding Pressure in Gases

• Pressure is the force from particles striking the container's walls
• Total pressure is the sum of pressures from all particles (assuming ideal behavior)

Mole Fraction

• Definition: Ratio of moles of a specific gas to total moles of gas present
• Formula: Partial Pressure = Mole Fraction × Total Pressure
• Example: 0.25 moles of gas in 1 mole total => Mole Fraction = 0.25
• If Total Pressure = 800 torr, then Partial Pressure = 200 torr

Example: Earth's Atmosphere

• Composition: Nitrogen, Oxygen, Argon, and trace gases
• Total pressure at sea level = 1 atmosphere
• Dalton's Law applied: Partial pressures of nitrogen, oxygen, and argon add up to total pressure

Calculation of Partial Pressures

• Use mole fractions derived from gas percentages
• Convert percentages to mole fractions (divide by 100)
• Multiply mole fractions by total pressure to find partial pressures
• Example: Partial pressures add up to 1 atmosphere

Advanced Calculations with Ideal Gas Law

• Given moles of different gases, known volume, and temperature
• Apply Ideal Gas Law to find total pressure
• Use mole fractions to calculate partial pressures of individual gases

Conclusion

• Dalton's Law is intuitive and useful for calculations of partial pressures in mixtures of gases.