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Day 5 – Notes. Unit: Gas Laws. Dalton’s Law of Partial Pressures, Grahams Law, and Real vs. Ideal Gases. After today you will be able to…. Describe Dalton’s law of partial pressures and calculate P total or a partial pressure
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Day 5– Notes Unit: Gas Laws Dalton’s Law of Partial Pressures, Grahams Law, and Real vs. Ideal Gases
After today you will be able to… • Describe Dalton’s law of partial pressures and calculate Ptotalor a partial pressure • Explain Graham’s law of effusion and calculate the rate at which gases effuse • Explain what is meant by the term “real” vs. “ideal” gases
Recall, gas pressure results from collisions of gas particles. • Gas pressure depends on the amount of gas and the KE of its particles. • Since particles in a mixture of gases at the same temperature contain the same average KE, the kind of particle is unimportant.
“The total pressure of a mixture of gases is equal to the sum of the individual (partial) pressures.”
Dalton’s Law of Partial Pressures Units of pressure must match! Ptotal= P1 + P2 + P3…
Example: Dalton’s Law What is the total pressure for a mixture of O2 and CO2 if PO2= 0.719 atm and PCO2= 423mmHg. PO2= 0.719atm PCO2=423mmHg 760mmHg x = 546mmHg 1atm Ptotal=546mmHg + 423mmHg Ptotal=969mmHg
Thomas Graham (1846) • Diffusion: Is the tendency of gas particles to spontaneously spread out until uniformly distributed. • Effusion: The escape of a gas through a tiny pinhole in a container of gas. • Gases with lower molar masses effuse more quickly.
“The rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass.”
Graham’s Law of Effusion Always place the larger molar mass in the numerator! Rate A√MMB Rate B √MMA =
Example: Graham’s Law Which gas effuses faster, H2 or Cl2? How much faster? Rate H2√MMCl2 Rate Cl2√MMH2 Rate H2√(70.90) Rate Cl2√(2.02) = = H2 effuses 5.92x faster than Cl2 = 5.92x
Real vs. Ideal Gases • The gas laws we’ve learned in this unit are based on a gas that behaves “ideally.” • An ideal gas has: • No molecular volume • No attractive forces • In reality, there are no perfectly ideal gases. But, under most conditions, real gases will approximate ideal gas behavior. • However, under certain conditions, real gases will deviate from ideal gas behavior.
Real vs. Ideal Gases • These deviations occur for: • High pressure: Gas particles are pushed closer together, more attractive forces result. • Low Temperature: The gas is compressed, there are more attractive forces. • High molar mass: Higher molar mass of the molecule usually means larger volume. • Polar molecules: Unequal sharing of electrons creates an attraction between molecules.
