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# Balancing chemical equations

How to balance a chemical reaction by making sure you have the same number of atoms of each element on both sides.

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• I'm working on Chemical Reactions: Double and Single Replacement on FLVS. Now my first question for this video is, how do you have 4 aluminum atoms when it says 2Al subscript 2? Do you just add the 2 and the subscript 2? Same thing goes with the O3. I am so lost.

My next question is...how would I write the charges out in this equation?
Would it be like this?
Al + O + O ----> Al + Al + O + O + O

I don't know if I'm doing it right or not. I am completely lost. If someone can help me, I would really appreciate it. Thanks :) • LOL. Hi Gabrielle M.
I do FLVS too.
For your first question, you multiply the whole number and the subscript.
For your second question, if I understand correctly, I would just right it as
2Al + 3O2 = 2AlO3 because when multiplying (as I said above) you will see how you helped make the equation balanced.

Don't worry, I was so lost and confused at the beginning too. I asked my teacher about it, watched the Khan Academy video (above) and took notes from my lesson and all started to untangle and make SO Much sense after all.
• • • Yes, ozone is found in the atmosphere at an overall concentration of 0.6 ppm.
But most of it is found in the upper atmosphere.
Ozone is highly unstable. It rapidly decomposes to oxygen in the lower atmosphere.
In the upper atmosphere (in the ozone layer), ultraviolet rays from the sun are constantly converting oxygen molecules into ozone, and the concentration of ozone there ranges from 2 to 8 ppm.
• At , since the equation reads 2Alsub2 Osub3, does the coefficient from 2Alsub2 apply to Osub3, or is it just assumed that we know that oxygen is doubled or something? • do you have to multiply each side by the same number?
Sorry I'm just a bit confused.
And also do you have to multiply each molecule? • We will have to multiply each sides by the same number if one of the molecules has a fractional value after balancing(1.5 for oxygen becomes 3 by multiplying every molecule on both sides by 2). However, when the reaction is not balanced(when both sides do not have equal number of atoms of every element) we multiply the value of the molecule/atom by a suitable number on the side where it has fewer atoms. We do this until the reaction is perfectly balanced and we are sure that the Law of Conservation of Mass is followed. I hope this answers your question.
• So no matter how many times I watch this video and how many times my Chemistry teacher explains it I cat seem to understand how to balance equations. If I have
N2+ H2---> NH3 what would I get and how would would I get that answer? I have a work sheet due on this this Wednesday so I need help fast. • Write it out on a piece of paper and underneath each side of the equation write out how many of each atom there are.

N2 + H2 -> NH3

On the left there is 2 N and 2 H
On the right there is 1 N and 3 H

If we tried to balance starting with H you'd need to use a fraction or decimal and would get messy, so let's start with N.
There's 2 on the left and 1 on the right, so we need to change the coefficient of NH3 to 2

Now we have
N2 + H2 -> 2NH3

Total the atoms up again:
On the left there is 2 N and 2 H still
On the right there is 2 N and 6 H now

So now all we need to do is make the left side have 6 H in total. So all we need to do is make the coefficient of H2 3

N2 + 3H2 -> 2NH3
• is the equation technically balanced already at ? say we don't care about molecules being half molecules. Just wanna make sure i understood • Can someone explain why in water (H20) the subscript isn't written after the O, because there is 2 Hydrogen and 2 Oxygen in the compound.? H2O2 isn't correct, however, it makes more sense to me. • • The coefficient in a balanced equation is an idea; the concept of telling the chemist that if the atoms, molecules and compounds are balanced, there are balanced amounts of the atoms, molecules and compounds on the other side in the product. It gives us a way to measure a reaction and use stoichiometry to gain the exact amounts desired of a specific product. You can read my explanation below to get an idea for this, but basically, the coefficient is just telling the chemist how much of a specific atom, molecule or compound it takes to gain the desired product.

So, balancing an equation is just like balancing the x in an algebraic equation... you need to make sure (because of the law of conservation of matter—matter cannot be destroyed or created) that if you have a definite amount of something on one side, you have an equal amount of it on the other side...
The equation (Mg) + (HCl) ⟶ (MgCl2) + (H2) is clearly unbalanced because on one side, there is only 1 hydrogen atom, but on the other side, there are 2 (also unbalanced Chlorine, but they both come from the same compound so this becomes really simple to balance).
This equation is easily balanced by placing the coefficient "2" in front of molecule (HCl) to form the balanced equation (Mg) + 2(HCl) ⟶ (MgCl2) + (H2).
you can think about it this way; 1 atom (Mg) + 2 compounds (HCl) combines in a reaction to form the products of 1 compound (MgCl2) + 1 Molecule (H2). 