How would you balance: Na + H2O --> NaOH + H2?

##2Na + 2H_2O -> 2NaOH +H_2##

You have to count the number of atoms in both sides of the reaction to be equal, to make it a little easier you can make a list. So in the equation ##Na+H_2O->NaOH+H_2##, there are ##1-Na-1## ##2-H-3## ##1-O-1## So you multiply NaOH and H2O by 2, so you have 4 hydrogens in both sides, and then multiply Na by 2 to be equal to the NaOH you previously multiplied.