**Where are we going with this?**This page will give the ability to

*demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.*

**Mole to Mole Stoichiometry**

*And so it begins! But… t*

*his is pretty simple… No, really.*

*Ignoring the fact that matter can become energy and all that… relativity stuff and E=mC*

^{2}…**The Law of Conservation of Matter: matter can neither be created nor destroyed.**

*So what?**A couple…*

*Now, about those compounds*… Remember this?

**Compounds are formed in specific, fixed ratios.**

__This__is when that kicks in and becomes useful!

**The balanced chemical reaction can be thought of as a recipe for compounds**. It tells the

**ratio of the parts**(reactants) that go together to form the product.

https://www.hersheys.com/kitchens/en_us/recipes/smores.html |

According to the Hershey's official website, a s'more is formed by combining a specific, fixed ratio of graham crackers, marshmallows, and chocolate.

That ratio is:

2 Crackers + 1 Marshmallow + 6 Chocolate Segments --> 1 S'moreSo, if you want to have 4 s'mores you need 8 crackers. If you want 10 S'mores, you need 10 Marshmallows.

The ratio for crackers, marshmallows, chocolate and s'mores is

2:1:6 --> 1

Pretty much anyone can figure out what is needed to make 8 s'mores.I'm not even going to type that out!

**The coefficients tell the ratios of the reactants and products.**

2Li + S --> Li2S

*confused only because we don't write coefficients of 1*) is

2:1 --> 1

If we know how many (or what fraction of a) **mole/s** of either reactant we have, we can easily find the other amounts (in **moles**).

**The Math: Ratios**

I'm going to propose this language usage: *The coefficients of a balanced chemical reaction are the basic ratio of reactants and products.*

So, if you have a basic ratio of

2:1 --> 2

then knowing how many moles of any part will allow you to convert to the other parts. How?

Consider the reaction of water…

2H2 + O2 --> 2H2O

The basic ratio is

2 : 1 --> 2

So, if we have 4 moles of hydrogen, we have 2 times as much hydrogen as we need for the basic ratio. Therefore, we can multiply ALL of the numbers by 2 to find out what we need and how much we will make.

2 : 1 --> 2

X 2

_________

4 : 2 --> 4

If we begin with 4 moles of hydrogen, we need 2 moles of oxygen and will make 4 moles of water. Bam!

Okay, let's talk about that red number! **Divide how many** moles **you have** of the thing **by how much is called for** in the basic ratio.

*Let's just make up a ratio…*

4 : 3 -- > 2

Let's say we have 2 moles of the first thing (we needed 4).

2 ÷ 4 = 0.5

So, we have **half** as much of the orange thing as we need. We multiply ALL of the ratio by 0.5 to get the moles that need to be actually present *(or that will be produced)*:

4 : 3 -- > 2

X 0.5

_________

2 : 1.5 --> 1

__________________*It is easy to "see" how this works with nice numbers, but it will work with any ugly decimal as well.*

Going with 4 : 3 -- > 2 again…

Suppose we have 0.23 moles of the thing we needed 4 moles of…

0.23 ÷ 4 = 0.0575

This means we have only a small fraction of what we need *(the orange thing)* for the basic ratio. But… we just multiply that number through the whole ratio:

4 : 3 -- > 2X 0.0575

_________________

.23 : 0.1725 --> 0.115

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