Chapter 5: Gases and the Kinetic-Molecular Theory

Merged flashcards from Chapter 5 of Chemistry: The Molecular Nature of Matter and Change.

Compressibility

Gas property where volume is strongly inverse to pressure

Temperature sensitivity

Gas property where volume is strongly associated with temperature, as gas particles move faster and around more

Flow

Gas property stating how gases can move freely and leak easily

Density

Gas property resulting in the measurement of g/L instead of g/mL due to extremely low levels of this

Solubility

The ability to form a solution when mixed; this is much more common in gases

Pressure

The force exerted on a surface over total area

Atmospheric pressure

The pressure of atmospheric gases at 0 degrees C and sea level

• Allows for crushing of cans without air

• Measured by barometers

Barometer

A device to measure atmospheric pressure by measuring the level of a liquid column (typically Hg) after outflows stop due to atmospheric pressure preventing loss

• Density is inversely proportional to height, making the dense Hg convenient for use in one

Manometer

A device to measure gas pressure

• Utilizes a U-tube filled with mercury to measure the level difference and thus the gas pressure (after accounting for atmospheric pressure in open-ended versions)

Ideal gas

A gas where the relationships between volume, pressure, temperature and amount are linear

0 degrees C at 1 atm

Standard temperature and pressure (STP)

Boyle’s law

Law stating that the volume of a gas is inversely related to its pressure

• V = 1/P

Charles’s law

Law stating that the pressure of a gas is linearly related to its temperature

• P = RT

Avogadro’s law

Law stating that the volume of a gas is linearly related to its amount at a fixed pressure and temperature

• V = Rn

22.4 L

Standard molar volume; this expresses the volume of 1 mol of gas at STP

Ideal gas law

The combination of the three gas laws

• PV = nRT

Universal gas constant

Denoted as R in the ideal gas law, it is the constant expressing 1 mol of gas at STP

• Is equal to roughly 0.0821 atm L / mol K

• Requires conversion of units when used

Density (d)

The measurement of mass per unit volume; in gases, it is inversely proportional to temperature and directly proportional to pressure

• Also mainly relies on molar mass due to fixed volumes per mole

Total pressure

In a gas, this is defined as the sum of the partial pressures contributed by each gas

Mole fraction (X)

The ratio of number of moles of solute to solvent

• Can be derived from the calculations of a gas’s total pressure: P_A = X_A(P_total)

  • If 25% of the mixture is A, 25% of the pressure comes from A as well

Gas collection

Performed through the heating of a reaction’s container to collect gases through a water-filled collection vessel

• This leads to a volume of gas added to water vapor

Vapor pressure

The added pressure of water vapor when collecting gas through a collection vessel, adding to the total pressure

• Depends on water temperature

Solve for the moles or unknown variables related to the gas, then convert to other units as normal.

How would I solve a gas stoichiometry problem?

Kinetic-molecular theory

Theory to explain the observed behaviors of gases; main points include:

• Negligible individual particle volume

• Random motion

• Elastic collisions without friction

• The same kinetic energy for a given temperature

Average kinetic energy

This is the same for gases at a given temperature, as E_k = ½(mass)(speed²)

• Mass being inversely proportional to speed enables a constant total energy

Effusion

The escape of individual gas particles through a small opening, the rate of which is governed by Graham’s Law

Diffusion

The movement of gases through another gas, governed by Graham’s Law

• Much slower than effusion due to increased particle collisions

Graham’s law

The law governing effusion and diffusion, starting that

• Rate of A = 1 / sqrt(M_A)