balance the eqn Na+H2O-NaOH+H2

Get the same amount of each element on each side.

Na + H₂O===>NaOH + H₂

There's one Na on the left and right, one O on the left and right but there's 2 H on the left and 3 H on the right so you need to make the H on left and right equal.


Na + 2H₂O===>2NaOH + H₂

Now the H on each side is equal because there's 4 H on the left and 4 H on the right but Now there's 1 Na on the left and 2 Na on the right so that's not balanced. You need to now balance Na. 

2Na + 2H₂O===>2NaOH + H₂

Now there's 2 Na on the left and 2 Na on the right, 4 H on the left and 4 H on the right, 2 O on the left and 2 O on the right so it's balanced. 

2Na + 2H₂O===>2NaOH + H₂

Hope it helps you...:)