Question

How do you balance `HBr + O_2 -> Br_2 + H_2O`?

Answer 1

`4HBr+O_2->2Br_2+2H_2O`

Explanation:

Add molecules (balancing numbers in front) to ensure that the number of atoms of each element is the same on the left and right hand sides of the equation.

Answer 2

`4"HBr"+"O"_2→2"Br"_2+2"H"_2"O"`

Explanation:

This equation is one of those where you need to balance O at the very beginning.

Otherwise as a thumb-rule one leaves H and O to taken up at the last.

Observe that in the unbalanced equation, on the reactants side there are 2 atoms of oxygen, whereas there is single oxygen atom on the products side.

Therefore to balance O on both sides, we need to put 2 in front of water molecule. This fixes 4 hydrogen atoms on the right side of the equation.

To balance 4H atoms in the products, we need 4 molecules HBr on the reactants side.

Now we are left with balancing of bromine atoms. Clearly to balance 4 Br atoms on the reactants side, we need to put 2 in front of `" Br"_2 ,` to balance the complete equation.