Ch. 8 - The Gas Phase

9% of MCAT Chemistry content

What are key properties of gases?

• Least dense phase of matter.

• Conform to the shape of their containers (fluids).

• Easily compressible.

What variables describe gas systems?

Temperature (T), Pressure (P), Volume (V), and Number of moles (n).

What are the important pressure equivalencies?

1atm = 760mmHg = 760torr = 101.325kPa.

How does a simple mercury barometer measure pressure?

• Increased pressure: Mercury rises in the column.

• Decreased pressure: Mercury level drops.

What is STP (Standard Temperature and Pressure)?

273K (0∘C) and 1 atm

What assumptions does the ideal gas law make?

• Gas molecules have negligible mass and volume.

• Equimolar amounts of gas occupy the same volume at the same temperature and pressure.

What is the volume of 1 mole of an ideal gas at STP?

22.4 L

What is the ideal gas law?

PV=nRT

What is Avogadro’s principle?

At constant pressure and temperature, V∝n (volume is proportional to moles).

What is Boyle’s law?

At constant temperature, P∝1/V (pressure and volume are inversely related).

What is Charles’s law?

At constant pressure, V∝T (volume and temperature are directly related).

What is Gay-Lussac’s law?

At constant volume, P∝T (pressure and temperature are directly related).

What is the combined gas law?

Combines Boyle’s, Charles’s, and Gay-Lussac’s laws:

(P1V1)/T1 = (P2V2)/T2

What does Dalton’s law of partial pressures state?

The total pressure of a gas mixture equals the sum of partial pressures of its components

What does Henry’s law state?

The amount of gas dissolved in solution is proportional to the partial pressure of the gas at the surface.

What are the assumptions of kinetic molecular theory?

• Gas particles have negligible volume.

• No intermolecular attractions/repulsions.

• Particles undergo random elastic collisions.

• Average kinetic energy is proportional to temperature.

What does Graham’s law describe?

Gases with lower molar masses diffuse/effuse faster than those with higher molar masses at the same temperature.

What is the difference between diffusion and effusion of gas?

• Diffusion: Spreading of gas particles from high to low concentration.

• Effusion: Gas movement through a small opening under pressure.

When do real gases deviate from ideal behavior?

• Moderate deviations: High pressure/low temperature cause gases to occupy less volume due to intermolecular attractions.

• Extreme deviations: High pressure/low temperature cause gases to occupy more volume due to physical particle space.

What corrects the ideal gas law for real gas behavior?

The van der Waals equation, which accounts for intermolecular attractions (a) and molecular volume (b).