A 600*cm^3600cm3 volume of ethane gas is completely combusted with 2500*cm^32500cm3 of dioxygen gas to give carbon dioxide and water. What is the reagent in excess, and what volume would CO_2(g)CO2(g) occupy after the reaction....?

1 Answer
Aug 20, 2017

The volume of carbon dioxide is "1200 cm"^31200 cm3. The volume of unused oxygen is "400 cm"^3400 cm3.

Explanation:

We are given the amounts of two reactants, so this is a limiting reactant problem.

We know that we will need a balanced equation with volumes of the compounds involved.

1. Gather all the information in one place.

color(white)(mmmmmmll) "2C"_2"H"_6 + color(white)(m)"7O"_2 → "4CO"_2 + "6H"_2"O"mmmmmmll2C2H6+m7O24CO2+6H2O
V"/cm"^3:color(white)(mmml)600color(white)(mmlll)2500V/cm3:mmml600mmlll2500
"Divide by:"color(white)(mmm)2color(white)(mmmml)7Divide by:mmm2mmmml7
"Moles rxn:"color(white)(mml)300color(white)(mmml)357Moles rxn:mml300mmml357

The molar quantities of the gases are directly proportional to the volumes, so we can use volumes as a measure of moles.

2. Identify the limiting reactant

An easy way to identify the limiting reactant is to calculate the "moles of reaction" each reactant will give.

You divide the moles of each reactant by its corresponding coefficient in the balanced equation.

I did that for you in the table above.

"C"_2"H"_6C2H6 is the limiting reactant because it gives the fewer moles of reaction.

3. Calculate the theoretical volume of "CO"_2CO2

"Theoretical yield" = 600 color(red)(cancel(color(black)("cm"^3 color(white)(l)"C"_2"H"_6))) × ("4 cm"^3color(white)(l) "CO"_2)/(2 color(red)(cancel(color(black)("cm"^3color(white)(l) "C"_2"H"_6)))) = "1200 cm"^3 color(white)(l)"CO"_2

4. Calculate the volume of "O"_2 used

"Volume of O"_2 = 600 color(red)(cancel(color(black)("cm"^3 color(white)(l)"C"_2"H"_6))) × ("7 cm"^3color(white)(l) "O"_2)/(2 color(red)(cancel(color(black)("cm"^3 color(white)(l)"C"_2"H"_6)))) = "2100 cm"^3color(white)(l) "O"_2

**5. Calculate the volume of "O"_2 remaining **

"Volume remaining" = "original volume - volume used" = "2500 cm"^3 - "2100 cm"^3 = "400 cm"^3