Balancing an equation??

Question

Write a balanced chemical equation for the combustion of C2H2 gas. One of the products is carbon dioxide. Be sure to include states of matter.

(The 2's are subscripts.)

Answer 1

2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(l)

Carbon: 4 → 4
Hydrogen: 4 → 4
Oxygen: 10 → 10
(Law of Conservation of Mass).
In other words, you can have atoms disappearing or coming out of no where.


edit:
To Gervald, you can't have 2.5 moles of a substance. Just multiply your coefficients by 2.

Answer 2

How about:

C2H2 + 2.5O2 ----> 2CO2 + H2O

All are gases except the water.