CLASSIFYING A CHEMICAL REACTION

Before you get anywhere with balancing or completing equations you have to be able to classify an equation because you have to identify whether your equation is a synthesis reaction, decomposition reaction, single replacement reaction, double replacement reaction, acid-base neutralization, or combustion. And if that all sounds confusing, don't worry I'll get to that in a moment. You are going to need to understand the 6 chemical reactions and there will be examples down below to help you with that, but without further ado lets get into it.

Here are the 6 chemical reaction types and what they do:

A, B, C, and D all represent variables so A could be Magnesium and B can be something else but these letters are a placeholder for what would be any element or polyatomic ion

Also as a side note please ignore the numbers before an element like example 2 for synthesis. We will get to that in a moment but I want you to focus on learning and recognizing the different reactions for now and just know by looking at an equation what type of reaction it is, we will get to balancing later...

Synthesis Reaction A + B ---> AB

Examples of Synthesis Reaction:

Mg + S ---> MgS

2Mg + O₂ ---> 2MgO

2Ba + Cl₂ ---> 2BaCl

Decomposition Reaction AB ---> A + B

Examples of Decomposition Reaction:

2KCl ---> 2K + Cl₂

BaS ---> Ba + S

2KClO₃ --> 2KCl + 3O₂

(this example is polyatomic so you will notice it doesn't follow the same steps, will touch on that later too)

Single Replacement Reaction A + BC ---> AC + B if A in this equation is a Metal

Single Replacement Reaction A + BC ---> BA + C if A in this equation is a Non-Metal

Examples of Single Replacement

2Na + MgCl₂ ---> 2NaCl + Mg (A in this equation [Na/Sodium] is a metal)

2Br + 2SrO ---> 2SrBr + O₂ (A in this equation [Br/Barium] is a non-metal)

Ca + BaO ---> CaO + Ba (A in this example [Ca/Calcium] is a metal)

Double Replacement Reaction AB + CD ---> AD + CB

or AB + CD ---> CB + AD (other way around doeesn't matter)

Double Replacement Examples:

2NaBr + MgCl₂ ---> MgBr₂ + 2NaCl

2KCl + MgO ---> K₂O + MgCl₂

3Rb₂Co + 2Na₃B ---> 2Rb₃B + 3Na₂Co

Acid-Base Neutralization {H}A + B{OH} ---> BA + H₂O

Examples of Acid-Base Neutralization:

H₂S + Ba(OH)₂ ---> BaS + 2H₂O

H₃P + 3NaOH ---> Na₃P + 3H₂O

HCl + NaOH --> NaCl + H₂O

1. Combustion Reaction A + O₂ ---> AₓOᵧ

2. Combustion Reaction CₓHᵧ + O₂ --> CO₂ + H₂O

1. Combustion Reaction Examples:

2Mg + O₂ ---> 2MgO

4Rh + 3O₂ ---> 2Rh₂O₃

2. Combustion Reaction Examples:

CH₄ + 2O₂ ---> CO₂ + 2H₂O

2C₈H₁₈ + 25O₂ --> 16CO₂ + 18H₂O

I have a video on this as well and here is the link: https://youtu.be/D0aJuKCyjoY

Video for Classifying Chemical Equations

Classifying And Balancing Chemical Equations: Text

BALANCING A CHEMICAL REACTION/EQUATION

Classifying And Balancing Chemical Equations: Text

You may have seen the numbers before elements like the last example:

2C₈H₁₈ + 25O₂ --> 16CO₂ + 18H₂O

and may be wondering what the 2 and the 25 or the 16 or 18 before the elements are and those numbers are called "Coefficients". Basically, the only time we use those is to Balance a chemical equation. Lets use an easier example like this one:

2KCl ---> 2K + Cl₂

As you notice there is a 2 in front of the KCl and a 2 in front of the K those are coefficients used to balance the equation. The real equation was:

KCl ---> K + Cl₂

but there are not the same amount of Cl (Chlorines) on the first side versus the second side...

KCl ---> K + Cl₂

One side of the equation has only 1 Chlorine and the other side has 2 chlorines and this means our equation is not balanced... We can make our equation balanced by adding a 2 in front of KCl and we should be done right? No...

2KCl ---> K + Cl₂

After adding the 2 in front of KCl sure the Chlorines are now balanced thats great but coefficients ALWAYS affect every element or polyatomic ion until it reaches a sign like a plus sign or arrow. So now that our chlorines are balanced our Potassium (K) was affected too and now we have 2 potassium's on one side and only 1 potassium on the other so to fix this we add another 2 before the K in the second side like this:

2KCl ---> 2K + Cl₂

and now you'll notice there are 2 chlorines and 2 Potassium's on both sides. If you want, here I have a video of me explaining this a little more clear

Watch the video below for a clear explanation of balancing chemical equations

Classifying And Balancing Chemical Equations: Text