Ideal Gases: Terms and Formulae

Terms

Absolute temperature

A temperature scale whose lowest possible value is zero. Absolute temperature is measured in Kelvin.
Absolute zero

A temperature where T = 0K. The theoretical lowest possible temperature.
Avogadro's law

Avogadro's law relates the amount and volume of a gas at constant temperature and pressure. Mathematically:

fracVn = k

k is a constant unique to the temperature and pressure.
Avogadro's number

N_A = 6.022×10²3. An avogadro's number of molecules equals one mole.
Boyle's law

A gas law relating pressure and volume for a fixed amount of gas at a constant temperature. Mathematically:

PV = C

C is a constant unique to the amount of gas and temperature.
Charles' law

A gas law relating volume and temperature for a fixed amount of gas at constant pressure. Mathematically:

= k

k is a constant unique to the amount of gas and pressure. Note that T must be an absolute temperature(in Kelvins).
Dalton's law

The total pressure of a mixture of gases is the sum of the pressures each constituent gas would exert alone. Mathematically:

P_tot = P_A + P_B + P_C + ƒƒƒ
Gas constant

Constant R in the ideal gas law. The value of R varies with the units of P, V, n, and T. The value of R can be deduced from the following table:

Units Value of R



0.08206



8.314



8.314



1.987



62.36
Ideal gas law

A gas law stating that PV = nRT. The two main assumptions of the law are that the molecules of an ideal gas do not have volume and do not interact with each other. The ideal gas law is a good approximation when the pressure is low and the temperature is high.
Isothermal conditions

Two or more conditions that share the same temperature. In other words, T is constant.
Kelvin

A unit of absolute temperature. Abbreviated with the letter "K." The Kelvin scale is related to the Celsius scale by T_K = T_C + 273.15. Kelvin should be used for all classical and ideal gas law calculations.
Manometer

A device used to measure the difference in pressure between two gases:

"A" and "B" represent the atmosphere, a vacuum, or a pressurized gas.
Molar mass

The mass of one mole of particles. Commonly expressed as g/mol.
Mole

One mole contains Avogadro's number (6.022×10²3) of particles. For example, one mole of H₂ would contain 6.022×10²3H₂ molecules. Moles are abbreviated as "mol."
Mole fraction

In a mixture of gases, the ratio that relates the number of moles of a constituent gas to the total number of moles in the mixture. Derived using the mole fraction formula.
Partial pressure

In a mixture of gases, the pressure exerted by one constituent gas. The sum of the partial pressures of gases in a mixture is equal to the total pressure of the mixture.
Standard atmospheric temperature and pressure

Conditions where T = 298K and P = 1bar.
Standard temperature and pressure (STP)

Conditions where T = 273K and P = 1atm.