B.3 Gas laws - Key terms

gas laws

laws of physics relating the temperature, volume and pressure of a fixed amount of a gas: Boyle’s law, Charles’ law and Gay-Lussac’s law

pressure, P

force acting normally per unit area: pressure = force/area (SI unit: pascal Pa), 1 Pa = 1 Nm⁻²

amount of gas

the quantity of gas in a container, expressed in term of the number of particles it contains

pascal

derived SI unit for pressure, 1 Pa = 1 Nm⁻²

atmospheric pressure

pressure due to the motions of the gas molecules in the air, can be considered as being due to the weight of the air above an area of 1 m², acts equally in all directions

amount of a substance, n

measure of the number of atomic-scale particles (atoms or molecules) it contains (SI unit: mole)

mole, mol

SI unit of amount of substance (fundamental)

Avogadro constant, Nₐ

the number of particles in 1 mole of a substance: 6.02 × 10²³

molar mass

the mass of a substance that contains 1 mole of its defining particles

circuit breaker

electromagnetic device used to disconnect an electrical circuit in the event of a fault

isothermal

occurring at constant temperature

Boyle’s law

pressure of a fixed amount of gas is inversely proportional to volume (at constant temperature)

Gay-Lussac’s law

for a fixed mass of gas with a constant volume, the pressure is proportional to the kelvin temperature

Charles’ law

volume of a fixed amount of gas is proportional to absolute temperature (at constant pressure)

empirical

based on observation or experiment

universal (molar) gas constant

the constant, R, that appears in the equation of state for an ideal gas (PV = nRT), R = 8.31 Jk⁻¹mol⁻¹

equation of state for an ideal gas, PV=nRT

describes the macroscopic physical behaviour of ideal gases, also called the ideal gas law

piston

a solid cylinder that fits tightly inside a hollow cylinder, trapping a fluid, designed to move as a result of pressure differences

PV diagram

a graphical way of representing changes to the state of a gas during a thermodynamic process

ideal gas

gas which obeys the ideal gas law perfectly, the microscopic particle model of an ideal gas makes several important assumptions about the particles and their motions

average value

any single number used to represent a quantity which is varying

range (data)

spread of data from smallest to largest values

anomalous

different from the pattern of other similar observations

outlier

a value which is signficantly different from the others in the same data set

mean

a certain type of average: the sum of all of the numbers divided by the number of values involved

dimensional analysis

method of checking if an equation may be correct, the units (dimensions) of all terms should be the same

internal energy of an ideal monoatomic gas, U

the sum of the random translational kinetic energies of all the molecules

real gases

modelling of gas behaviour is idealized, real gases do not behave exactly the same as the model of an ideal gas