how many moles of water are needed to react with 4.00 moles of sodium?

Question

2Na + H2O- Na2O + H2

Answer 1

the balanced chemical equation tells us the mole ratios needed.

 

Looking at the balanced equation, we know that for every 1 mole of water reacted, we need 2 moles of sodium.

 

I like to set it up as fractions...

 

2moles Na =  4moles Na

1mole H₂O     xmoles H₂O

 

Now just cross multiply and solve for x.

 

(2)(x)=(1)(4)

2x=4

x=2 moles H₂O

 

Now, it's possible you could have did that it in your head, and that's true. But more than likely, in class, you will be given decimals that are not nice whole numbers, and you will have to do it this way. better to practice it now with easier numbers until you have the hang of it.

 

It doesn't matter how you set it up, as long as the same chemical/compound is in the same spot (numerator or denominator) in both fractions. We would get the same answer if we had it moles water over moles sodium.