Transcription
To be able to show what's happening in a chemical reaction, you need to understand chemical equations. One way to show a reaction is with a word equation. Imagine we're told that methane burns in oxygen, turning into carbon dioxide and water.
On the left-hand side of our equation, we have the methane and oxygen that reacted together, and we call these the reactants. On the right, we have the molecules that are produced; so, in this case, carbon dioxide and water, which we call the products. And in the middle, we have a single arrow to show that the reactants react completely to form the products.
More often, though, instead of writing these word equations, we write symbol equations using the chemical symbols of each molecule involved. So we would have CH₄, which is methane, plus O₂ going to form CO₂ plus H₂O. Notice that I've put O₂ rather than O. That's because oxygen exists as a molecule made up of two atoms. So whenever you include oxygen in a reaction, you have to put O₂. Just like for chlorine, you would put Cl₂, and for nitrogen, N₂.
Anyway, getting back to our equation, it's not quite right just yet because we haven't balanced it. In order to be balanced, chemical equations need to have the same total number of each type of atom on either side of the arrow. In our example, we can see that on the left of the arrow there's one carbon, four hydrogens, and two oxygens, whilst on the right there's one carbon, two hydrogens, and three oxygens. So our equation isn't balanced. Somehow, we need to increase the number of oxygens on the left-hand side and increase the number of hydrogens on the right.
Now, it's absolutely fine if you can't work out how to balance it in one go. Often, balancing equations is a process of trial and error where you keep on changing numbers until you get the answer. The first rule of balancing equations is that we can't change any of the little numbers. This is because doing so would mean that we were changing the actual type of chemicals in our equation. For example, we couldn't change our O₂ to an O₃ because O₃ is an entirely different substance, which isn't oxygen. Instead, we have to rely on changing the big numbers in front of the different elements or compounds, as this number just represents how many of that substance there are.
So, to increase the number of oxygen atoms on the left, we'd have to put a 2 in front of the O₂, meaning we now have 2 oxygen molecules and, therefore, 4 oxygen atoms in total on the left-hand side. This might seem a bit weird as we only need three oxygen atoms to match the right-hand side, so shouldn't we just make it one and a half molecules of oxygen? Unfortunately, we can't. When balancing chemical equations, another rule is that we need to keep the whole numbers, and so we have to round up to two instead and keep four oxygen atoms. This leaves us needing two more hydrogens and one more oxygen on the right, which we can get by increasing the number of water molecules from one to two. So we now have the same number of each type of atom on both sides of the reaction, and so we're done.
Let's quickly try one more example: sulfuric acid plus sodium hydroxide goes to form sodium sulfate plus water. On the left, we have three hydrogens, one sulfur, five oxygens, and one sodium; while on the right, we have two hydrogens, one sulfur, five oxygens, and two sodiums. Although it's up to you, I recommend balancing the least common elements first, which in this case would be sulfur and sodium. As sulfur is already balanced with one on either side, I'd look at sodium, where we can see that we need one more on the left. So to fix this, I put a 2 in front of the sodium hydroxide, giving us two sodiums. Then, if we count all of our atoms again, we can see that we need two more hydrogens and one more oxygen on the right-hand side. This is a pretty common problem to have, and we can fix it by adding one more water molecule to the right. As always, when you think you're done, just double-check to see if it's balanced. So we've got four hydrogens, one sulfur, six oxygens, and two sodium atoms on each side, so this is exactly balanced, and we're finished.
Anyway, that's all for now, so hope you enjoyed the video, and we'll see you next time.