Question

25.6 grams of sodium reacts with an excess of oxygen. How many grams of sodium oxide will be produced

Answer 1

First, find the equation for $Na+ O = NaO$

Oxygen hangs out in groups of 2 when alone so you have 
$Na+ O_{2} = NaO$

Next, to balance NaO you see that Na has a charge of +1 and O has -2
You need 2 Na for the one O and now you have
$Na+ O_{2} = Na_2O$

Now you need to balance. 2 Os are on the left so make $Na_2O$
$2Na_2O$    Now you have 4 Na on the right, just make Na, 4Na

Now you have the equation $4Na+O_2=2Na_2O$

Transfer grams to moles:
Divide the given grams (25.6) by the atomic weight of our variable (Na = 22.99)
25.6/22.99= 1.11352762   This is the number of moles you have.

Use the ratio of the amount of the element or compound to the one you want
It'll look like this $\frac{4Na}{2Na_2O} = \frac{1.11352762}{x}$ 
Multiply 1.11352762 by 2 then divide by 4 leaving you with 0.55676381

Finally, multiply that by the atomic mass of $Na_2O$
Na2 = 22.99*2 = 45.98+ O = 16 =

61.98g of $Na_2O$ is your answer