Let me ask you: what is the point of Chemistry? Some might say it is about understanding the molecular properties of substances, and how they react with other substances. Others might broadly say that Chemistry deals with elements, chemicals, and compounds. A third group might entertainingly remark that it is about experiments and setting things on fire. Well, regardless of which viewpoint you align yourself with, you’d be correct! Chemistry encompasses everything mentioned above. Alas, to stop there would be a major injustice to the subject as a whole. You see, to fully answer the question requires a deeper sense of specificity. How do you document a chemical reaction? What exactly happened when you mixed those two chemicals? Why did you get the results you did? There is a crucial part of Chemistry that is often overlooked. This post is going to shed light on that very important piece: namely, the chemical equation. We’re going to look at the purpose of these equations, why they are important, and what they show us about any given reaction. To succeed in Chemistry, you need to know the full story. Now, you get that chance!
So, first thing is first – what is a chemical equation? Chemical equations are textual representations of reactions. They show the reactants that started the experiment as well as the resulting products. Often times the two are separated by an arrow, which merely signifies that a reaction did in fact occur. An example of a simple chemical equation is below:
Can you see why these chemical equations are important? They offer a quick representation that shows how molecules react with each other. It is clear how each molecule of oxygen and hydrogen reacted and where they went in the experiment. Now, for the example above, it may seem kind of obvious. But not all equations will be that simple! Take the example below, based on the reaction of vinegar and baking soda:
The same equation, just with the compound names:
Acetic Acid + Sodium Bicarbonate —> Sodium Acetate + Water + Carbon Dioxide
Neither one looks very easy, does it? Well, now let me ask you this question, based upon the reaction: where are the carbon atoms located? How do they change between reactants and products? The easiest way to answer this is to look at the chemical equation, as it clearly shows each atom and compound. Yes, you could answer the question with the compound names formula, but do you really know off the top of your head how many carbon atoms are in sodium acetate, if any at all? (Maybe your science professors would!). Trust me when I say that equations come in all forms and complexities within the world of Chemistry. Looking at chemical equations make analyzing them so much simpler!
BALANCING A CHEMICAL EQUATION
Now, as is common with all branches of science, you may not always have the information necessary to answer a specific question or problem. Sometimes, you might find yourself being given a skeleton equation, and asked to find how many atoms of a certain element are present within it. A skeleton equation is an equation that shows which reactants create which products, but do not provide quantitative information. Using the original (and much simpler) example above, the skeleton equation would be: H2 + O2 —> H2O. This equation does show the compounds involved, but doesn’t show how many hydrogen, oxygen, or water compounds are in the reaction. To figure this out, you would have to balance the equation. This is something you are probably familiar with by now (or at least have heard about it). This is a process that is relatively simple to do, and can be quite beneficial for understanding any equation given to you.
So how do you do it? The simple answer: make sure the number of atoms of an element are the same on both sides of the equation. So, let’s use our example above. The left side has two hydrogen atoms (H2) and two oxygen atoms (O2). The right side has two hydrogen atoms, but only one oxygen atom (H2O). Needless to say these two do not equal. In chemical reactions, you cannot have an atom disappear – it will always be present in one form or another. So, to get the oxygens to be equal, you need to add a two in front of the product. This gives you the following: H2 + O2 —> 2H2O. The left side has two hydrogens and two oxygens. The other side now has four hydrogens and two oxygens (**see note below for clarification**). As you can see, it is now balanc-….uh oh. We have a problem. We have too many hydrogens on the right side. The equation doesn’t balance. To fix this, add a coefficient of two to the hydrogens on the left side. Doing so now gives us: 2H2 + O2 —> 2H2O. Let’s check the atom numbers again. Left side has four hydrogens and two oxygens. Right side has four hydrogens and two oxygens. We have a match! This equation is now balanced! As you can see, sometimes it is necessary to change the numerical value (through coefficients ONLY – you cannot change subscripts) of compounds on both sides to balance an equation. On some equations, I find myself “bouncing” back and forth between both sides quite frequently. More examples can be found on the worksheet at the bottom of this post.
**NOTE: This is merely a clarification of the compound 2H2O. If you understand why it has 4 hydrogens and 2 oxygens, then you can skip this paragraph. For those of you that don’t, the concept isn’t too difficult. The 2 coefficient is distributed throughout the compound that it is connected to. This applies to all compounds in Chemistry. So, the two really means two H2 and two O. For hydrogen, the subscript and coefficient multiply together, giving a total of four atoms. Make sense? Another way of looking at it is to say 2H2O means two of the entire compound. If it is easier, view 2H2O as being “H2O + H2O”.
IDENTIFYING TYPES OF CHEMICAL EQUATIONS
Ok, so you have balancing pretty much figured out now! But this isn’t the only important thing that a chemical equation can show us! It can also demonstrate the type of reaction that occurs. To explain the different types, I’m going to refer to a lab that I did in my own Chemistry class. This lab was actually a compilation of seven different “mini-labs”; all of which were related under the same idea. Below is a basic overview of each lab. For each lab, I have included the word, skeleton, and balanced equations (just in case if you want more practice balancing them).
The procedure involved taking a test tube filled half way with Hydrochloric Acid, dropping in a piece of magnesium, and placing a second inverted test tube over the ensuing reaction. Then, we quickly moved the inverted test tube horizontally, lit a match, and recorded the results. Check out the video below of the lab; be sure to pay special attention to the sound produced after we light the match, towards the end.
This lab can be represented in the following ways:
- Word Equation: Hydrochloric Acid + Magnesium –> Hydrogen + Magnesium Chloride
- Skeleton Equation: HCl + Mg –> H2 + MgCl2
- Balanced Equation: 2HCl + Mg –> H2 + MgCl2
This lab is very simplistic both in design and execution, and yet it is still by far my favorite lab of the entire series. The procedure is simple: light a Bunsen burner, take a small strip of magnesium and hold it in the flames, and watch the reaction. There is only one way to explain what happens – you create Heavenly Light. Don’t believe me? Check it out:
This lab can be represented in the following ways:
- Word Equation: Magnesium + Oxygen –(Heat)–> Magnesium Oxide
- Skeleton Equation: Mg + O2 –(Heat)–> MgO
- Balanced Equation: 2Mg + O2 –(Heat)–> 2MgO
Lab number three is very similar to lab number two. This time, instead of burning magnesium, we were tasked with burning copper in a Bunsen Burner. It is important to note that before we subjected the copper to the flame, we first shined it with sand paper (which removes any foreign particles on the wire). The end result was a wire that had “graphite-reminiscent” ash on it, and an increased malleability.
We created the following equation to represent the lab:
- Word Equation: Copper + Oxygen –(Heat)–> Copper (II) Oxide
- Skeleton Equation: Cu+ O2 –(Heat)–> CuO
- Balanced Equation: 2Cu + O2 –(Heat)–> 2CuO
This lab involved putting a small amount of Ammonium Carbonate into a test tube, and heating the test tube. Then, we were supposed to smell the gas produced (through wafting, of course). The gas smelled like ammonia. It is also important to note that the Ammonium Carbonate in the test tube slowly diminished until it completely disappeared.
This lab can be represented in the following ways:
- Word Equation: Ammonium Carbonate –(Heat)–> Ammonia + Carbon Dioxide + Oxygen
- Skeleton Equation: (NH4)2 + CO3 –(Heat)–> NH3 + CO2 + H2O
- Balanced Equation: (NH4)2 + CO3 –(Heat)–> 2NH3 + CO2 + H2O
The next lab we did involved half a test tube of hydrogen peroxide, and a small amount of manganese dioxide added to it. The events of this lab came after we ignited a splint, waved out the flame, and inserted it into the test tube. The end result was a splint that reignited itself! How cool is that? Check it out:
- Word Equation: Hydrogen Peroxide + Manganese Dioxide –> Manganese Dioxide + Oxygen + Water
- Skeleton Equation: H2O2 + MO2 –> MO2 + H2O + O2
- Balanced Equation: 2H2O2 + MO2 –> MO2 + 2H2O + O2
Lab number six! This lab involves placing a few drops of different chemicals into a well plate. One well l received Potassium Iodide. The other received Lead (II) Nitrate. Both solutions are clear in color. However, when you mix them together, they turn into a vibrant (I would go so far as to say canary) yellow color. Pretty cool, huh?
- Word Equation: Potassium Iodide + Lead (II) Nitrate –> Lead (II) Iodide + Potassium Nitrate
- Skeleton Equation: KI + Pb (NO3)2 –> PbI2 + K(NO3)
- Balanced Equation: 2KI + Pb(NO3)2 –> PbI2 + 2K(NO3)
The final lab had a test tube containing Copper (II) Carbonate being heated . A second, inverted test tube was placed to collect any gas that was released. Then, we ignited a wood splint and placed it in the inverted test tube. The end result was a flame that would be extinguished by the gases (the exact opposite as lab number five, mind you!). Check it out:
- Word Equation: Copper (II) Carbonate –(Heat)–> Carbon Dioxide + Copper (II) Oxide
- Skeleton Equation: CuCO3 –(Heat)–> CO2 + CuO
- Balanced Equation: CuCO3 –(Heat)–> CO2 + CuO
I can hear you saying it already: what is the point of all of these labs? Why did I spend the time showing them to you? Well, they all are wonderful examples of the five different types of reactions that substances can undergo. It is one thing for me to merely tell you the reaction types (which I will in a second). But to tell you what they are, and provide real-world examples of them is so much more beneficial! Feel free to go back to the labs above and look at the equations to see why they are the reaction type that they are. The reaction types themselves are simply stated down below:
- Synthesis Reaction: When two substances combine to form a compound. A+B –> AB
*Refer to labs 2 and 3.
- Decomposition Reaction: When a compound separates into two substances. AB –> A+B
*Refer to labs 4, 5, and 7.
- Single-Replacement Reaction: Also known as a Displacement Reaction, this occurs when a substance “trades” places with a substance in a compound. A + BC –> AC + B
*Refer to lab 1.
- Double Replacement Reaction: When two substances in two compounds switch places. (Everyone switches places).
AB + CD –> CB + AD
*Refer to lab 6.
- Combustion Reaction: When a compound and oxygen react to produce heat and a new compound (usually being water and/or carbon dioxide). Fuel + O2 –(Energy)–> H2O + CO2
*There are no above labs that are combustion reactions. However, the following are examples:
Propane: C3H8 + O2 –> H2O + CO2
Octane: C8H18 + O2 –> H2O + CO2
That about does it everyone! I know this has been a super long post, but I appreciate you hanging in there! This is a very important part of Chemistry – one that will make your understanding of all future experiments that much simpler! Below is a worksheet containing additional examples of balanced chemical equations, as well as the type of equation that they represent if you need it. Otherwise, good job and happy studying!