sulfur dioxide (g) + oxygen (g) sulfur trioxide (g)

Question

SO2 + O = SO3

Is this correct for the balanced equation?

Answer 1

No. Don't get carried away with trying to balance the equation by changing the subscripts. In fact, a good rule to remember is this.
1. Write the reactants and products.
SO2 + O2 ==> SO3 (You must have O2 since oxygen is a diatomic molecule. We don't have just O floating around.)
RULE # 2. You may NOT change any subscripts.
3. Balance by changing ONLY the coefficients.
4. 2SO2 + O2 ==> 2SO3