Question

Blank c2h4 + blank o2 → blank co2 + blank h2o how many moles of o2 are in the chemical equation when balanced using the lowest whole numbers

Answer 1

The reaction is
C₂H₄ + O₂ → CO₂ + H₂O

To balance the equation, both side have same number of elements. Here,

In left hand side has                                            in right hand side has

           4 H atoms                                                       2 H atoms 

           2 C atoms                                                       1 C atom 

           2 O atoms                                                       3 O atoms 

First, we have to balance number of C atoms and number of H atoms in both side.  
To balance C atoms, '2' should be added before CO₂ and to balance H atoms, '2' should be added before H₂O. 
Then number of oxygen atoms is 2 x 2 + 2 = 6 in right hand side. So, 3 should be added before O₂ in left hand side.
After balancing the equation should be,

C₂H₄ + 3O₂ → 2CO₂ + 2H₂O