Question

8) When a mixture of 10.0 g of ethane (C₂H₆) and 10.0 g of oxygen (O₂) is ignited, the resultant combustion reaction produces CO₂ and H₂O.

a) Write a balanced chemical equation for this reaction.

b) What is the limiting reagent?

c) How many grams of C₂H₆, O₂, CO₂, and H₂O are present after the reaction is complete?

d) Show that mass is conserved in this reaction.

Answer 1

a) C2H6 + 7/2O2 --> 2CO₂ + 3H₂O

b) as per the stoichiometry of equation 1 mole of ethane will react with 3.5 moles of oxygen

Molecular weight of ethane = 30 g / mole

Molecular weight of O2 = 32

So 30 grams of ethane will need 3.5 X 32 grams of oxygen

so 10 grams of ethane will need = 3.5 X 32 X 10 / 30 = 37.33 grams of oxygen

So limiting reagent is oxygen

c) After completion of reaction

10 grams of oxygen (10/32 moles) will react completely with 2.67 grams of ethane (2.67 / 30 moles =0.089 moles)

As per stoichiometry, 1 mole of ethane will give two moles of CO2 and 3 moles of H2O

so 0.089 moles will give 0.178 moles of CO2 and 0.267 moles H2O

The CO2 left in the mixture = 10-2.67 = 7.33 grams

CO2 = 0.178 X 44 = 7.832 grams

H2O = 0.267 X 18 = 4.806 grams

d) intial mass = 10 +10 = 20 grams

After reaction mass = 7.832 + 4.806 + 7.33 = 19.968 = 20 approx

so mass is conserved