Reactants and Products?

Question

Total confusion for me. What do I need to do first? Check to see if it is balanced or no?

In the acetylene torch, acetylene gas (C2H2) burns in oxygen to produce carbon dioxide and water.
2 C2H2(g) + 5 O2(g) 4 CO2(g) + 2 H2O(g)

(a) How many moles of O2 are needed to react with 2.00 moles of C2H2?

(b) How many moles of CO2 are produced when 4.5 moles of C2H2 reacts?

I can't breath

ok I got the first answer to my question figured out once I calmed down. 5.00 was the answer to part a.

Answer 1

Its just a matter of ratios

There are 5 moles of O2 for every 2 moles of C2H2.

So if you start with 2 moles of C2H2, just multiply by 5/2

The ratio of CO2 to C2H2 is 4/2. So multiply 4.5 moles by 4/2

Answer 2

2moles of C2H2->4 Moles of CO2
1mole of C2H2 ->2moles of CO2
4.5mole of C2H2->4.5 x 2 mole of CO2=9moles