Moles and gas volumesMoles and gas volumes

Calculate the amount of substance in moles, using gas volumes

04/20/23

Avogadro’s LawAvogadro’s Law

Equal volumes of gases at the same temperature and pressure contain equal numbers of

molecules

i.e. 100cm3 of hydrogen at some temperature and pressure contains exactly the same number of molecules as 100cm3 of carbon dioxide

• One mole of different gases– Note the same volume of each gas has a different

mass

ExampleExampleCH4(g) + 2O2(g) CO2(g) + 2H2O(l)

•The equation says you need twice as many molecules of oxygen as you do of methane. According to Avogadro’s Law, this means you will need twice the volume of oxygen as of methane.

•So, if you have to burn 1 litre of methane, you will need 2 litres of oxygen.

•You should also produce 1 litre of carbon dioxide

•Because water is a liquid, we don’t know how much of that we get

Units of volumeUnits of volume

• Note:1 litre = 1dm3 = 1000cm3

n = V/24(dm3)

Thi notes

ProblemsProblems

• Take the molar volume to be 24.0dm3 at rtp.a) Calculate the mass of 200cm3 of chlorine gas

(Cl2) at rtp

b) Calculate the density of argon (Ar) at rtp.c) Calculate the volume occupied by 0.16g of

oxygen (O2) at rtp.

d) If a gas has a density of 1.42g dm-3 at rtp, calculate the mass of 1 mole of the gas