Balancing Equations for Chemistry (Explanations)

Here are the answers to the equations in my last post: Balancing Chemical Equations Step by Step.  When you balance equations, the most important thing is to keep an accurate count of all of your atoms as you go through the process.  This becomes even more important when you have to balance molecules that have parentheses within themselves. Yes, they get more complicated, but if you can do basic chemical equations, you will know what to do with the crazier ones that take more effort and eraser dust.

___ N₂ + ____H₂ ------>  ___NH₃

My attention immediately goes to the 3 Hydrogen atoms in NH₃ since it's the most abundant atom.  There is no number that we can put in front of the H₂ to make it equal to the 3 Hydrogens on the right side.

The first thing I think to do is multiply the subscripts to produce a number they both will divide into.  3x2=6  and we can get 6 Hydrogen atoms on each side by adding a 3 on the left side and a 2 on the product side:


___ N₂ +  3H₂ ------>  2NH₃

Now count everything.  We have 2 Nitrogen atoms and 6 Hydrogen atoms on the left side.  And we have 2 Nitrogen atoms and 6 Hydrogen atoms on the right side.

What?  We're done?  Yep.   Here's the balanced equation.


N₂ +  3H₂ ------>   2NH₃




___S₈ + ___O2 ------->  ____SO₃

You can probably predict where my eyes go.  My focus goes to the S8 since it has the most atoms.   We need to get 8 Sulfur on the right side, too.  So just put an 8 over there.

___S₈ + ___O₂ ------->  8SO₃

Now you have 8 Sulfur atoms and 2 Oxygen atoms on the left.  We have 8 Sulfur atoms and 24 Oxygen atoms on the right.  The Sulfur is balanced on both sides, but the Oxygen is not.  We now need 24 Oxygen atoms on the left.  We do that by placing a 12 in front of the O₂.

S₈ +  12 O2 ------->  8SO₃

Bam! Balanced equation.




___N₂ + ___O₂ -------> ____ N₂O


Alright.  We can already see that there is the same amount of Nitrogen on each side (2 atoms).  So we have to deal with the Oxygen because there are 2 Oxygen atoms on the left reactant side but only one on the right.

So let's add a 2 to the right to balance the Oxygen.

 ___N₂ + ___O₂ ------->  2N₂O

In doing this, we've changed the amount of Nitrogen on the right of the arrow so that its no longer balanced.  Now there are 2 Nitrogen atoms on the left and 4 Nitrogen atoms on the right.  To fix this we simply must add a 2 to the reactant Nitrogen on the left like so:

  2N₂ +  O2 ------->  2N₂O

And we are done!



___HgO ------> ____Hg + O₂

This one is really easy.   Let's balance the Oxygen.  There are 2 Oxygen on the right.  Just add 2 to the HgO to balance the Oxygen to have 2 atoms on each side of the arrow.

2HgO ------> ____Hg + O₂
 
In doing this, we've increased the Mercury (Hg) to 2 atoms.  All we must do is add 2 to the Hg on the right to balance this problem.

 2HgO ------>  2Hg + O₂

 And Voila!


____CO₂ + ____H₂O ----->  ___C₆H₁₂O₆ +____ O₂

Uh oh.  This one looks a little intimidating, right?  Don't worry.  Just keep count and break it down.

I'd tackle the 12 Hydrogen in the C₆H₁₂O₆ molecule first. How do we get 12 Hydrogen on the left side?  All we do is put a 6 in front of the H2_O.

____CO₂ +  6H₂O ----->  ___C₆H₁₂O₆ +____ O₂

 Now on the left side we have:  1 Carbon atom, 8 Oxygen atoms and 12 Hydrogen atoms
And on the right side we have:  6 Carbon atoms, 8 Oxygen atoms and 12 Hydrogen atoms.

What I would do is then add a 6 to the CO₂.

6CO₂ +  6H₂O ----->  ___C₆H₁₂O₆ +____ O₂

Now on the left we have: 6 Carbon atoms, 18 Oxygen atoms and 12 Hydrogen atoms.
And on the right we still have our 6 Carbon atoms, 8 Oxygen atoms and 12 Hydrogen atoms.

So how do we balance out the Oxygen?  Well, we need to get 18 Oxygen on the right. Just add 6 to the O2 on the right.

 6CO₂ +  6H₂O ----->  C₆H₁₂O₆ + 6O₂


 Now on the left: 6 Carbon, 18 Oxygen, 12 Hydrogen
And on the right: 6 Carbon, 18 Oxygen, 12 Hydrogen

I call that balanced.


___Zn + __HCl ------->  ____ZnCl₂  + ___ H₂

  After that one, this one should be super easy.  Add a 2 to the HCl to balance the Chlorine.
Zn +  2HCl ------->  ZnCl₂  + H₂
 

There are: 1 Zinc atom, 2 Hydrogen atoms and 2 Chloride atoms on both sides---and we have a balanced equation.