Avogdro's Law and Gas Volume Calculations

Question 1

what did scientists discover about how gases reacted with each other in the 19th century

Answer 1

• the volumes of gases that react are in a whole number ratio
• provided that the volumes are measured under the same conditions of temperature and pressure

Question 2

what is an example of how this ratio works with the formation of water

Answer 2

• two moles of hydrogen react with one mole of oxygen

- making the ratio of hydrogen to water 2:1

Question 3

what does avogadros law state

Answer 3

that equal volumes of gas under the same conditions of temperature and pressure contain the same number of molecules

Question 4

why is avogadros law very useful when it comes to calculations

Answer 4

• because it allows us to use volumes for calculations rather than the masses of gases
• measuring the volumes of gases is a lot easier than measuring their mass
• so it a lot easier to use volumes instead

Question 5

what is the overarching concept that is used form avogadros law when calculating gas reactions

Answer 5

• that one mole of every gas occupies exactly the same volume
• for a given temp and pressure

Question 6

as avogadros law also applies to the numbers of molecules that react, how could you describe the reaction N2 + 3H2 = 2NH3

Answer 6

• you could say that one molecule of nitrogen gas reacts with three molecules of hydrogen gas to form 2 molecules of ammonia
• but the law allows us to say that 1 volume of nitrogen reacts with 3 volumes of hydrogen to form 2 volumes of ammonia

Question 7

for the reaction H2 + Cl2 = 2HCl(g), 100cm^3 of hydrogen and 100cm^3 of chlorine were mixed together and reacted. what volume of hydrochloric acid would be produced

Answer 7

200cm^3

Question 8

what are the two methods you couldve used to come to your answer

Answer 8

• because only one product is formed, all of the reactants must have formed the hydrochloric acid
• so 100 + 100 = 200cm^3
• you could also compare the ratios
• the ratio was 1:1:2 with one volume of H2 and Cl2 but two volumes of HCl
• so if the ratio of HCl is double that of the reactants, the volume must also be double

Question 9

for the reaction CO2 + C = 2CO, 1dm^3 of CO2 was reacted with excess carbon, what volume of carbon monoxide was produced and why

Answer 9

• 2dm^3
• the carbon is solid so its volume cant be considered
• meaning the only ratio is between carbon dioxide and monoxide
• as it is 1:2 you simply double the volume of carbon dioxides
• giving you 2

Question 10

in the reaction 2NO + O2 = 2NO2, 50cm^3 of nitrogen monoxide reacts with 25cm^3 of oxygen. what volume of nitrogen dioxide is formed and why

Answer 10

• 50cm^3, not 75
• if you look at the ratios it is 2:1:2
• meaning that the volume of nitrogen dioxide is equal to that of the monoxides

Question 11

in the equation 2SO2 + O2 = 2SO3, 200cm^3 of sulfur dioxide is mixed with 200cm^3 of oxygen. what volume of sulfur trioxide will be produced and why

Answer 11

• 200cm^3
• the volumes are equal so you cant use the ratio of 2:1:2
• but you see that all the sulfur dioxide reacts but it can only react with half the volume of oxygen available
• leaving you with 200cm^3 of troixde but with 100cm^3 unreacted oxygen gas left over

Question 12

in the reaction CH4 + 2O2 = CO2 + 2H2O, 100cm3 of methane is mixed with 100cm3 of oxygen and reacted. what volume of gas is formed and why

Answer 12

• the volumes dont equal the ratio 1:2:1:2 so this cant be used
• as you are asked about the volume of gas formed you need to calculate the total (all reactants)
• from the equation you see that all the oxygen will react but only with half the amount of methane
• meaning 50cm3 of methane reacts with 100cm3 of oxygen to form 100cm3 of carbon dioxide and 50cm3 of water
• 50 + 100 = 150cm3 of gas with 50cm3 methane left over

Question 13

in the equation 2H2S + 3O2 = 2SO2 + 2H2O(l) 250cm3 of hydrogen sulfide reacts with 600cm3 of oxygen. what is the resulting gaseous mixture

Answer 13

• the ratio of the gases is 2:3:2
• meaning that the whole 250cm3 of 2H2S reacts with (250x1.5) = 375cm3 of 3O2 due to the ratio
• as there are two volumes of SO2 like for hydrogen sulfide, you also get 250cm3 of that being fromed
• the resulting gasoues mixture is all of their volumes added up
• so you have no more 2H2S with (600-375) = 225cm3 of oxygen and 250cm3 of sulfur dioxide
• 225 + 250 = 475cm3