C2h4 3 o2 2 co2 2 h2o
a. when 0.624 mol o2 are reacted, how many moles of carbon dioxide are produced?

Use the question marck Moles of CO2
The the giving = 0.624 mol O2
Find the CF faction = 1 mole=  32.00 of O2

O= 2x16.00= 32.00amu ( writte this in the cf fraction)
SET UP THE CHART
Always start with the giving

0.624 mol O2    /  1mol of CO2
  / = Cancel the queal ( O2)
                       / 32.00c O2
                      /
                     /
Multiply the top and divide by the bottom 
0.624 mol CO x 1mol CO2 = 0.624 divide by 32.00 O2 =0.0195
You should look at the giving number ( how many num u gor ever there) 
Ur answer should have the same # as ur givin so 
= 0.0195 
= .0195 mol of CO2