Gases and Kinetic-Molecular Theory - Vocabulary Flashcards

Vocabulary flashcards covering key terms and concepts from Topic 1: Gases and Kinetic-Molecular Theory.

Expansibility

Gases expand to fill the entire container; they have limitless expansibility due to their negligible molecular size relative to the container.

Compressibility

Gases are easily compressed by applying pressure, reducing their volume.

Diffusibility

Gases diffuse rapidly through each other to form a homogeneous mixture.

Pressure

Force exerted by gas molecules per unit surface area on the container walls.

Effect of Heat

When a gas is heated, its pressure increases (or its volume increases if the container allows).

Volume (V)

The space occupied by a gas in a container; measured in liters (L).

Pressure (P)

Force per unit area exerted by gas molecules on container walls.

Temperature (T)

Absolute temperature used in gas problems, measured in Kelvin (K).

Moles (n)

Amount of substance; number of moles of gas in the container.

Atmospheric pressure

Pressure exerted by the Earth's atmosphere; commonly taken as 1 atm.

Boyle’s Law

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure; PV is constant.

Inverse proportionality

A relationship where one quantity increases as the other decreases.

PV = k

Product of pressure and volume is constant for a fixed amount of gas at constant T and n.

P1V1 = P2V2

Relation between initial and final P and V when T and n are constant.

Charles’s Law

At constant pressure, the volume is directly proportional to absolute temperature (V ∝ T).

Absolute temperature

Temperature on the Kelvin scale, T(K) = T(°C) + 273.15.

Kelvin scale

Temperature scale used for gas laws; zero is absolute zero.

V ∝ T

Volume is directly proportional to temperature at constant pressure and amount.

Combined Gas Law

Relates P, V, and T for a fixed amount of gas: P1V1/T1 = P2V2/T2.

Avogadro’s Law

At the same T and P, equal volumes contain equal numbers of moles; V ∝ n.

Molar Gas Volume

Volume occupied by 1 mole of gas at a given T and P; at STP, 22.4 L per mole.

Gay-Lussac’s Law

At constant volume, pressure is directly proportional to absolute temperature (P ∝ T).

Molar Mass / Molecular Weight

Mass per mole of a substance, expressed in g/mol.

Density

Mass per unit volume (ρ = m/V); for gases, density increases with molar mass and decreases with temperature.

Ideal Gas Law

PV = nRT; an equation of state for an ideal gas relating P, V, n, and T.

Equation of State

A relation among the thermodynamic variables describing a gas (e.g., P, V, T, n).

Gas Constant (R)

Proportionality constant in the ideal gas equation; R ≈ 0.0821 L·atm·mol⁻¹·K⁻¹ (or 8.314 J·mol⁻¹·K⁻¹ in SI).

STP

Standard Temperature and Pressure: 0°C (273.15 K) and 1 atm.

Molar volume at STP

The volume occupied by one mole of an ideal gas at STP; about 22.4 L.

Density formula ρ = PM/RT

Density of a gas expressed in terms of its pressure, molar mass, and temperature.

Partial pressure

Pressure contributed by an individual gas in a mixture (Pi).

Dalton’s Law of Partial Pressures

Total pressure of a gas mixture equals the sum of the partial pressures of each component: Ptotal = P1 + P2 + …

Mole fraction (X)

Fraction of moles of a component in a mixture: Xi = ni/ntotal.

Graham’s Law of Diffusion

Rates of diffusion are inversely proportional to the square roots of molar masses: r1/r2 = sqrt(M2/M1).

Diffusion

Spontaneous mixing of gas molecules due to random motion.

Effusion

Escape of a gas through a small pinhole into a region of lower pressure.

Kinetic-Molecular Theory

Model describing gases as many tiny moving particles with elastic collisions and negligible intermolecular forces.

Ideal Gas

Gas that perfectly follows gas laws under all conditions; no intermolecular forces and negligible molecular volume.

Real Gas

Gas that deviates from ideal behavior due to finite molecular size and intermolecular attractions, especially at high pressure or low temperature.

Van der Waals Equation

Real-gas equation: (P + a(n/V)²)(V − nb) = nRT; accounts for intermolecular attractions (a) and finite volume (b).

Van der Waals constants a and b

Gas-specific constants: a accounts for attractions between molecules; b accounts for finite molecular volume.