Gas Laws Flashcards
What is Boyle’s Law?
Boyles Law states that at a constant temperature the volume of a given mass of gas varies inversely with the absolute pressure.
Aka PV= constant (k1)
(memory tip to remember which law is boyle’s think of a boil/spot volume of pus under pressure)
What is Charles’s Law?
Charles’s Law states that at a constant pressure the volume of a mass of gas varies directly with absolute temperature.
Aka V/T = constant (k2)
What is the 3rd or Gay-Lassau’s Law?
The 3rd gas law at a constant volume the absolute pressure of a given mass varies directly with the absolute temperature.
P/T = constant (k3)
You have a 10litre oxygen cylinder, its pressure gage reads 137bar, how much oxygen do you have available for transfer?
137bar is ~ 13700kPa
The absolute pressure is the gage pressure + atmospheric pressure ~13700 +100=13800KPa
P1xV1=P2xV2
13800Kpa x 10L = 100Kpa x V2
138000/100= V2
=1380L
10L must remain in the cylinder therefore you have 1370L of O2 available for the transfer.
How can you express the combined (ideal) gas law?
PV/T = nR
n= number of moles
R= universal gas constant
What does Avogadro’s principle state?
Avogadro’s Principle states that equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
Aka 1 litre of O2 and CO2 and N2 would all contain the same number of molecules (but the weight will vary depending on the mass of the molecules)
What is standard temperature and pressure?
Standard temperature is 273.15 kelvin or 0 degrees celsius
Standard pressure is 1 atmosphere
What is the volume of 1 mole of any given gas at standard temp and pressure?
22.4L
What is the mass of 22.4L of CO2 at standard temperature and pressure?
22.4L = 1 mole of CO2
Mass number of C is 12 therefore 1 mole contains 12g
Mass number of O is 16 therefore 1 mole contains 16g
12g + (16gx2) = 44g
What is the value of the universal gas constant?
R= 8.31 J/K x mol
A full cylinder of nitrous oxide contains 3.4 kg of nitrous oxide, but how much gas are you able to get out of the cylinder? (assume the cylinder is at standard temp and pressure)
Step 1: The molecular weight of nitrous oxide is 44, therefore 1 mole is 44 g. (N mass number = 14 O mass number =16)
Step 2: If you were using the cylinder at STP, you know that 1 mole will occupy 22.4 litres.
Step 3: If the cylinder contains 3400 g of nitrous oxide, you have 3400/44 moles, which is 77.2 moles. Therefore you will have 77.2 moles x 22.4 litres, which is 1730 litres of nitrous oxide at STP.
Don’t forget that there will be a residual volume in the cylinder which will be unavailable, aka whatever the volume of the cylinder is.
What is Dalston’s Law of partial pressures?
Dalton’s Law of Partial Pressures states, that 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.
I.e. If you had a sealed container of room air with a pressure of 100kPa, then the partial pressure of O2 in the container would be 21kPa and the partial pressure of N2 would be approximately 79kPa.
Taking into account Dalston’s law of partial pressures re-write the ideal/combined gas law?
PV/T= (n1 + n2 ….) R
n1 = number of moles of the 1st gas
n2 = number of moles of the 2nd gas
When do gases not conform to the ideal gas law?
At very low temperatures if enough pressure is applied then a gas will liquefy.
What is the critical temperature?
The critical temperature is the temperature above which a substance cannot be liquefied however much pressure is applied.
This could also be thought of as the temperature below which a gas can be liquefied if enough pressure is applied.
The critical temperature varies between each gas.
Below its critical temperature a gas is referred to as a vapour.
