3. When a mixture of 10.0 grams of acetylene (C2H2) and 10.0 grams of oxygen (O2) is ignited, the resulting combustion reaction produces CO2 and H2O.

Question

A) Write a balanced equation for this reaction.
B) What is the limiting reactant?
C) How many grams of C2, H2, O2, CO2, and H2O are present after the reaction is complete?

Answer 1

2C2H2 + 5O2 ==> 4CO2 + 2H2O

b.
mols C2H2 = grams/molar mass
mols O2 = grams/molar mass
Using the coefficients in the balanced equation, convert mols C2H2 to mols CO2.
Do the same for mols O2.
It is likely that the two values for mols CO2 will not be the same which means one of them is wrong. The correct value in limiting reagent problems is ALWAYS the smaller value and the reagent producing that number is the limiting reagent. Then convert grams to mols by g = mols x molar mass.

c.
After you have determined the limiting reagent, use that value and the procedure above to calculate mols CO2 and mols H2O formed.
Use the same procedure using the limiting reagent to determine the mols of the non-limiting reagent used and subtract from the initial amount to determine the value after the reaction.