Gas Laws Flashcards
Boyle’s Law
Boyle’s Law states that at a constant temperature the volume of a given mass of gas varies inversely with the absolute pressure.
V∝1/P or PV= constant (k1)
Charles’s Law
Charles’s Law states that at a constant pressure the volume of a given mass varies directly with the absolute temperature.
V∝T or V/T = constant (k2)
Gay-Lussac’s Law
The third gas law states that at a constant volume the absolute pressure of a given mass varies directly with the absolute temperature.
P∝T or P/T = constant (k3)
The Combined Gas Law
PV/T = C
Derivation of the Combined Gas Law:
- Boyle’s Law states that at a constant temperature: PV = constant
- Charles’s Law states that at a constant pressure: V/T = constant
- The third gas law states that at a constant volume: P/T = constant
- Therefore combining all 3 laws gives: PV/T = constant
Avogadro’s Principle
Def mole
Avogadro’s Number
Avogadro’s Principle states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
A mole is the quantity of substance containing the same number of particles as there are atoms in 12 g of carbon 12. This is equal to 6.022 x 1023.
one mole of any gas at standard temperature and pressure occupies 22.4 litres.
Thus, 44 g of nitrous oxide or 32 g of oxygen would each occupy a volume of 22.4 litres at standard temperature and pressure (standard pressure and temperature (STP) is defined as 1 atm and 273.15 K).
Ideal Gas Law
PV = nRT
number of moles of gas present, n.
R has a value of 8.31 J K-1 mol-1. (Nernst equation)
The ideal gas law is derived from the combined gas law and Avogadro’s number.
- The combined gas law states the PV/T = C
- The constant (C) is directly proportional to the amount of gas, n, which is Avogadro’s Law
- The proportionality factor is the universal gas constant R therefore C = nR.
Dalton’s Law of Partial Pressures
In a mixture of gases the pressure exerted by each gas is the same as that which it would exert if it alone occupied the container.
Ptot = P1 + P2 + P3
PV = (n1 +n2 …)RT
Critical temperature
Critical temperature of N2O
Critical temperatire of O2
The critical temperature is the temperature above which a substance cannot be liquefied however much pressure is applied.
- 5°C
- 119°C
Critical pressure
The critical pressure is the saturated vapour pressure of a substance at its critical temperature.
Saturated vapour pressure?
The partial pressure exerted by the vapour at equilibrium is called saturated vapour pressure (SVP).
Henry’s law
Henry’s law states that at a fixed temperature, the amount of a given gas dissolved in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid. In other words, the higher the pressure, the more the dissolved gas
Henry’s law applies at a constant temperature. As the temperature increases, gas bubbles out of the liquid. Conversely, the solubility increases as the temperature decreases.
Solubility coefficient:
Bunsen
Ostwald
Solutions of gases are described as volumes of gas dissolved in a volume of liquid.
Bunsen: the volume of gas corrected to standard temperature and pressure (STP) dissolved in a unit volume of a liquid at the temperature concerned where the partial pressure of the gas above the liquid is one atmosphere
Ostwald: the volume of gas dissolved in a unit volume of liquid at the temperature concerned
Partition Coefficient
The partition coefficient is the ratio of the amount of a given substance present in one phase compared with another, both phases being of equal volume and at equilibrium.
Gas Tension
The term ‘gas tension’ can be used instead of ‘partial pressure’. The tension of a gas in solution is the partial pressure of the gas in equilibrium with it
