Chemical equations

0:00- [Instructor] If you take hydrogen and react it with oxygen with a spark, then it explodes to give you water. And the big question is how do you communicate this chemical change or this chemical reaction that just occurred? Well, one way is you could just write it out.

0:13You could say that, Hey, when hydrogen reacts with, when hydrogen react, oh no, that's gonna take a lot of time. I'm not gonna write that down. Another way to communicate this is, for example, we can draw. So we could, for example, draw hydrogen. Here's one, hydrogen, oh my god, that's gonna take a lot of time as well.

0:33So the big question that you wanna try and answer in this video is what is, how can we efficiently communicate chemical reactions and chemical changes? So let's find that out. The first step is to remember chemical formulas. Remember chemical formulas tell us how many atoms of each element are present in a molecule or a compound.

0:51For example, if you look at the chemical formula H2 or H represents hydrogen, so this is a chemical formula for hydrogen, but what does it represent? Well, the subscript two, remember, so you can see that there's a subscript over here, that subscript two says that there are two atoms of hydrogen in this unit, all right?

1:08So if you could visualize it, we'd visualize it this way. There are two atoms of hydrogen over here. Okay, what about this one? This substance is oxygen. And the two subscript here shows that there are two atoms of oxygen in this unit, all right? And finally we have the chemical formula for water.

1:24What does this say? Well, in one unit of water, we'll have two atoms of hydrogen, because there's subscript two and one atom of oxygen. If there's no subscript, it means there's only one. So two atoms of hydrogen and one atom of oxygen connected together to give you one unit of water or one molecule of water over here.

1:41Okay, so that's the chemical formula. Now that we have this, we are ready to find out the most efficient way to communicate chemical changes. And that is via chemical equations. But what exactly is a chemical equation? Well, the best way to learn about them is directly with an example.

1:55So let's say the most efficient way to communicate the reaction that we spoke about right here goes, boom. Okay, let's break this down, okay? First of all, you can see some stuff on the left side of the arrow mark. These are called the reactants. And the stuff on the right side of the arrow mark are called the products.

2:12So over here we have two reactants and we have one product. And now, here's how we read it. We will say, hydrogen reacts with oxygen to produce water. There you go. Okay, let's take some more examples. Here's another example. In this example, you can see there's only one reactant and two products.

2:36So since it's not reacting with anything else, this is breaking apart, okay? So here's how we would read it. We would say calcium carbonate, and don't worry about the names, we'll learn about them slowly and steadily. But calcium carbonate breaks or decomposes to produce calcium oxide and carbon dioxide.

2:58All right, let's try one last, and this time we have two reactants and two products. So the way we would say read this is copper reacts with silver nitrate to produce copper nitrate and silver. There you go. This now brings us to the last concept and the most important concept, and that is the law of conservation of matter, which says matter can neither be created nor destroyed, which means in our case, atoms can neither be created nor destroyed.

3:30Remember, in a chemical reaction, atoms only rearrange to form new stuff. So this means for every element, the number of atoms on the left side should exactly equal the number of atoms of those elements on the right side, and it's important to check for that. So let's see how to check that in chemical equations.

3:51So let's start with the first one. Okay, so here we have to make sure that the number of atoms for hydrogen and oxygen are the same on the left and on the right. And the best way to check for that is to actually write it down and keep track of it. Let's start with hydrogen, okay?

4:05Let's look at how many atoms we have on the left and how many we have on the right. So let's look at the ones on the left. We know that over here this subscript says that there are two atoms of hydrogen in one unit, meaning one molecule of hydrogen, right? Now, what does this two says?

4:20This two is called the coefficient. It says that there are total two units or two molecules of hydrogen altogether. So this is one molecule of hydrogen, and this is the second molecule of hydrogen. There are two molecules of hydrogen reacting over here. So in total, how many hydrogen atoms do we have?

4:38We have 1, 2, 3, 4. So there are four hydrogen atoms on the left, and the best way to actually quickly get this is to multiply the coefficient with the subscript. Two times two is four. Okay, let's count that on the right hand side. On the right hand side, again, this subscript says there are two atoms of hydrogen in one molecule of water.

5:00So here's a molecule of water with two atoms of hydrogen. But what does this coefficient say? This coefficient says that, Hey, there are two molecules of water altogether. So this is the first molecule and this is the second molecule of water. And so the total number of hydrogen atoms, how many do we have?

5:141, 2, 3, 4, four. And so it works out, we have exactly four on the left, four on the right. So no atoms of hydrogen are created or destroyed, perfect. Let's confirm the number of oxygen atoms on the left is exactly the same as that on the right. Okay, on the left hand side, we see a two subscript, which says there are two atoms of oxygen in one molecule.

5:37All right, and what is the coefficient? Well, if there's nothing written, it means one, and it means there's only one molecule of oxygen reacting over here. So this is it. So how many atoms of oxygen do we have on the left? We have two. Okay, how many atoms of oxygen do we have on the right side?

5:52Well, we can just count over here. We can see indeed there are two, but you could done another way. You could have just looked at this coefficient multiplied with the subscript over here and said two times one, which is two, and you get the same result. And there you go.

6:06No atoms of oxygen are created or destroyed over here. And so law of conservation of matter holds for this particular equation. In other words, we also say this chemical equation is balanced. Okay, your turn, why don't you look at this one and count the number of atoms of each element on the left and right, and see if it's balanced or not.

6:28All right, let's do this. So how many carbons do we have on the left? Well, we have carbon here. Subscriber is one, and there's only one coefficient. So one times one is just one. Same is the case over here. One times one is one, and so we have one each. What about hydrogen?

6:43Well, we have four over here, and there's only one coefficient so one four is four. How many do we have on the right? Well, we have a subscript two. and we have a coefficient of two. So two times two is four. What about oxygen? Well, oxygen on the left, we have two here, and there's two here.

7:00So two times two is four, so we have four on the left. And how many on the right? Well, we have two over here. And what about over here, is it one? No, no, remember, we have to multiply with the coefficient. There are two molecules of water. So two times one is two, and therefore you get two plus two, which is four.

7:16There we have it, this equation is also balanced. So long story short, chemical equations are the best way to communicate chemical changes or chemical reactions. Substance on the left side of the arrow marks are called reactants. And on the right side of the arrow marks are called products.

7:31And the arrow marks, which separates the reactants from the products, you know, represents a change that has happened. And different substances are separated by a plus sign. And most importantly, according to the law of conservation of matter, matter can neither be created nor destroyed, which means that atoms cannot be created nor destroyed in a chemical reaction.

7:48They only rearrange themselves. And that's why it's important to count them. And the best way to count them is to look at the coefficient, look at the subscript, and then multiply them. And you count them and make sure that they're, you know, the number of atoms for each element is the same on the left and on the right.