IB Chemistry S1.5 Ideal Gases

Vocabulary flashcards covering the IB Chemistry topic on Ideal Gases, gas law equations, conversions, kinetic model assumptions, and real gas deviations.

Ideal Gas

A theoretical gas model consisting of point particles in constant random motion with negligible particle volume, no intermolecular forces, continuous random straight-line motion between collisions, and perfectly elastic collisions.

Elastic Collisions

Collisions between gas particles or container walls in which kinetic energy is conserved and the duration of each collision is far less than the time between collisions.

Temperature (Kinetic Theory)

A measure of the average kinetic energy of the particles in a gas sample.

Pressure (Kinetic Theory)

The time-averaged, isotropic force per unit area produced by gas particles colliding with the container walls.

Internal Energy of an Ideal Gas

The total energy of an ideal gas, which depends solely on temperature and is independent of volume or pressure.

Ideal Gas Equation

The equation $PV = nRT$ where $P$ is pressure in $Pa$ ($N\,m^{-2}$), $V$ is volume in $m^3$, $n$ is amount of substance in $mol$, $R = 8.31\,J\,mol^{-1}\,K^{-1}$ is the gas constant, and $T$ is absolute temperature in $K$.

Combined Gas Law

The relation $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$ used to evaluate a fixed amount of gas changing between two sets of conditions.

Standard Temperature and Pressure (STP)

Standard reference conditions defined as a temperature of $273\,K$ and a pressure of $1.00 \times 10^5\,Pa$.

Molar Volume ($V_m$)

The volume occupied by one mole of gas at specified temperature and pressure, which equals approximately $22.7\,dm^3\,mol^{-1}$ at STP.

P-V Relationship (at Constant Temperature)

An inverse relationship where $P \cdot V = \text{constant}$, forming a rectangular hyperbola on a $P$ vs $V$ plot and a straight line on a $P$ vs $\frac{1}{V}$ plot.

V-T Relationship (at Constant Pressure)

A directly proportional relationship between volume and absolute temperature, forming a straight line through the origin when temperature is measured in Kelvin ($K$).

P-T Relationship (at Constant Volume)

A directly proportional relationship between pressure and absolute temperature, forming a straight line through the origin when temperature is measured in Kelvin ($K$).

Low Temperature Deviation

Non-ideal gas behavior caused by reduced kinetic energy, allowing attractive intermolecular forces (IMFs) to become significant and lower the pressure relative to ideal predictions, leading to condensation.

High Pressure Deviation

Non-ideal gas behavior caused by packing particles close together, making the finite molecular volume non-negligible and raising the pressure above ideal predictions due to repulsive forces.

Conditions Closest to Ideal Behavior

High temperature, low pressure, and small or nonpolar molecules such as $He$, $Ne$, $H_2$, and $N_2$.

Volume Conversions for Ideal Gas Calculations

Conversion factors where $1\,dm^3 = 1\,L = 1 \times 10^{-3}\,m^3$ and $1\,cm^3 = 1\,mL = 1 \times 10^{-6}\,m^3$.

Pressure Conversions for Ideal Gas Calculations

Conversion factors where $1\,atm = 1.01325 \times 10^5\,Pa$ with $1\,Pa = 1\,N\,m^{-2}$.

Ammonia Vapour Deviation

The deviation of $NH_3$ vapour from ideal behavior upon cooling due to strong intermolecular hydrogen bonding, unlike nonpolar monatomic $Ne$.