eLFH - Gas Laws Flashcards
Boyle’s law
At a constant temperature, the volume of a given mass of gas is inversely proportional to the absolute pressure
P x V = constant
Aka: P1 x V1 = P2 x V2
How to calculate volume of gas that can be delivered from cylinder from gauge pressure
Use Boyle’s Law
P1 x V1 = P2 x V2
Therefore V2 = (P1 x V1) / P2
Convert units to kPa
P1 = Gauge pressure + atmospheric pressure (to give absolute pressure)
V1 = cylinder volume
P2 = atmospheric pressure
V2 therefore is volume delivered (but remember volume of cannister will remain inside once pressures equalise so minus that from total volume to be delivered)
Eg. 10 L cylinder with gauge pressure 137 bar
P1 = 137 bar + 1 bar = 138 bar = 13,800 kPa
P2 = 1 bar = 100 kPa
V1 = 10 L
V2 = (P1 x V1) / P2
= (13,800 x 10) / 100
= 1380 L
(Total volume delivered = 1380L - 10L which will remain in cylinder)
Total gas delivery = 1370 L
Charles’ Law
At a constant pressure, the volume of a given mass of gas is directly proportional with the absolute temperature
V / T = constant
V1 / T1 = V2 / T2
Gay-Lussac’s Law
At a constant volume, the absolute pressure of a given mass of gas is directly proportional to the absolute temperature
P / T = constant
P1 / T1 = P2 / T2
Combined gas law
Combining all 3 gas laws gives following equation:
PV / T = C
Therefore:
(P1 x V1) / T1 = (P2 x V2) / T2
Temperature must be in Kelvin, but pressure and volume can be in any units as long as they are consistent on both sides
Avogadro’s Principle
Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules
Mole definition
A mole is the quantity of substance containing the same number of particles as there are atoms in it
I.e 12 g of Carbon 12 will contain 1 mole (6.022 x 10^23 particles)
and 16 g od Oxygen 16 will also contain 1 mole
This number of particles is known as Avogadro’s constant - 6.022 x 10^23
Avogadro’s constant
6.022 x 10^23
Number of particles in 1 mole
Volume of 1 mole of any gas at standard temperature and pressure
22.4 Litres
Standard temperature
273.15 Kelvin
Standard pressure
1 atmosphere
Ideal Gas Law
(Combined gas law with Avogadro’s law)
PV / T = C
Constant will vary according to number of moles present (n)
Therefore C = nR
Where R is the universal gas constant and n is number of moles
Therefore PV / T = nR
Usually written as PV = nRT
Universal gas constant (R) value
8.31 J / K / mol
Same R is in Nernst Equation
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 were alone in the container
Total pressure within a container = sum of individual pressures exerted by each gas
P tot = P1 + P2 + P3 +…
I.e
PV = (n1 + n2 +…) RT
Critical temperature
The temperature above which a gas cannot be liquified no matter how much pressure is applied
Different temperature for different gases
Critical pressure
Saturated vapour pressure of a substance at its critical temperature
Gas vs Vapour
Gas is a substance above its critical temperature
Vapour is a substance below its critical temperature
Critical temperature of oxygen
- 119 degrees Celsius
Factors which make real gases deviate further from the ideal gas
Decrease in temperature
Increase in pressure
Volume that one mole of a gas will occupy at standard pressure and temperature
22.4 L
Henry’s Law
At a constant temperature, the amount of gas dissolved in a solvent is proportional to its partial pressure above the solvent
