Skip to main content
Loading Explore guides…
Chemical Reactions Basics · Acedra
Home
Explore
Chemistry
Chemical Reactions Basics
Sign in to save
Chat
If YouTube asks you to sign in, open the video on YouTube.
Watch on YouTube
Reload player
Transcript
45 segments
Copy
Hide video
0:00
>> All right, class. So in this chapter, it's actually really fun, we're going to talk about chemical reactions. A lot of things on a daily basis that you do are chemical reactions, you just don't think about it. You drove to school. You don't go to school right now, you drove somewhere today, you did chemical reactions. You cooked, you did a chemical reaction. You washed your hands, hopefully you did a lot of that, you did a chemical reaction. So all those things are chemical reactions,
0:26
you just don't think about it. Now, some chemical reactions are simple, some of chemical reactions are more complex. But doesn't it matter how complex or simple a chemical reaction is, you can always write a chemical equation. So, when you write a chemical equation, you're going to write the reactant on the left side, you're going to put an arrow, and you're going to write the product on the right side. Okay? And so, I want to give you an example of a chemical reaction here.
0:55
N2 gas plus H2 gas goes to ammonia gas. So one thing you probably notice that every time you have a chemical reaction like this one, what you have to do, you have to mention the phases for each compound. We have to mention the state. Is it solid, is it liquid, is it gas? In this case, it was gas, so I put a little g. So if it's solid, you put s, liquid l, gas g. And if it dissolved in water, and we're going to go over this one later, you put aq for aqueous. So aq would be aqueous.
1:31
And then we're going to go over that a little bit later what that is, but you have to mention the phases, you have to put the state of each compound atom. Now, the only thing to always remember that every time I gave you a chemical reaction, every time I give you a chemical equation, the first thing that you need to do is? Balance it. You need to balance the chemical equation. Don't forget balance-- it's so hard to write on this board. You have to balance it. Don't assume that it's balanced.
2:06
You have to balance it. Now, what do I mean by balancing chemical equation, chemical reaction? What that means is you have to have exactly the same number of atoms on each side, okay? So you have to have exactly the same number of atoms on each side. So let's give it you a shot over here. Over here, how many nitrogen do I have? I have 2 nitrogen. But right here, I only have 1 nitrogen. That cannot be happening. So then what do you do to balance a chemical reaction? You use coefficients, right?
2:43
So I'm going to put a 2 over here. So now I have 2 nitrogen, it matches with 2 nitrogen over there. Now how many hydrogen do you have? You have have 3 hydrogen, do you agree? You have-- sorry, 2 nitrogen. I can't do math. You have 2 hydrogen over here. How many hydrogen do you have here? Be careful. You have 6 hydrogen over here. You see it? Because I put a coefficient 2, so I have 6 hydrogen over here now. So what do I do? I add a 3 over here. 3 times 2 is also 6.
3:20
So now, 2 nitrogen, 2 hydrogen, 6 hydrogen, and 6 hydrogen. So I've balanced this equation. Again, every time I give you a chemical equation, the first thing you need to do, you need to balance it. Don't assume it's balanced. What that means is, you have to make sure that we have the same number of atoms on those side. And when we balance it, we balance it by adding the coefficient. Never change the compound. You cannot change the compound. That's the balanced compound equation.
3:50
You cannot mess with the formula, right? This is NH3, that's a balanced neutral compound? You can't mess with those. The only thing you can do, you can put a coefficient behind it. We're good so far? Okay. Yeah, let's do another easy one. Let's do another easy one, and I'll give you a hard one to balance. When you drive your car, N2 plus 02 goes to NO2, that's going on in your car engine. And then those are all gases. Now, quickly balance this for me.
4:28
Again, you have to have the same number of atoms on both side. N, so I have 2 nitrogen here, 1 here. What I'm going to do, I'm going to add a coefficients, so you don't change the compound. You cannot change the compound, right? This is NO2. This is my compound that I'm for. These are the reactants I'm using. You can never change the compound. The only thing you can do is to add the coefficients, okay? So you balance the equation by adding coefficients. Okay. So, I added a 2 here.
5:04
So now I have 2 nitrogen, 2 nitrogen. But how many oxygen do I have here now?
5:09
Here now you have 2NO2, so I have 4 oxygen all together. So what do I have to do? I have to add a 2 over here. I have to add a 2 over here. So far, so good? Okay, now I do want you to remember this that all chemical reactions are all around us. Chemical reactions are all around us. Now, just for fun, we're going to balance one more chemical reaction. And then we got to go over and categorize chemical reaction. So hopefully, you've had this before, and you're good at balancing chemical reactions.
5:50
But let's do one more, because I want to give you one.
5:56
Oh, my God, this is not coming up. Oh, all right. Sodium phosphate, plus magnesium fluoride goes to magnesium phosphate
6:22
plus NaCl.
6:24
It's a long one. I'm not going to put the state of phases on there, but that's okay. I want you to get a little practice on balancing chemical reaction. So I just gave you a chemical reaction, and pretty long one. Now the question is, this chemical reaction, how would you balance it? How would you balance this chemical reaction? And what did we talk about? What we said we have to have the same number of atoms on both sides, okay? Now, before you balance it, I want to give you a hint.
7:02
When you have reactions like this that have polyatomic ions, here's a hint. This is going to make your life much easier. Balance the polyatomic ion as one unit.
7:17
Balance the polyatomic ion as one unit. What do I mean by that? What I mean by that, don't try to say, "Oh, I have 1 phosphorus, 4 oxygen. I have 2 phosphorus, 8 oxygen. No no no no. PO4 is a polyatomic ion, right? So balance it as one unit. So here I have 1 phosphate here. What I have here, I have 2 phosphate over here. So taking that in, balance this chemical reaction. This is much harder than the first example. And remember, here's my hint, look at polyatomic ions
7:57
as one unit when you're balancing it. So you have 1 phosphate, you have 2 phosphate. That's how you should look at it. Don't say I have 1 phosphate, 4 oxygen. No, you have 1 phosphate, you have 2 phosphate. All right. Did you balance that? Now, if you balance this, let's see. Let's see if we can do it together. This is a hard one, but we can do this. So, like I said, here, you have 2 phosphate, and you have 1 phosphate here. So what am I going to do? I'm going to add a 2 over here.
8:33
So now I have 2 phosphate, and I have 2 phosphate here, right? Because PO42, I have two of these. So far, so good. Now because I added coefficient here, now that I have 2 phosphate, how many sodium do I have? 2 times 3 is 3. Now I have 6 sodium. If I look at over here, I only have 1 sodium. So I'm going to add a 6 over here, okay? Now that I added this, how many Cl do I have? I have 6 sodium, that's great because I have 6 sodium over there. But how many Cl I have? Now I also has 6 Cl, right?
9:14
Because when I add a 6 over here, now what I have, I have 6NaCl, 6Na and 6Cl. So here, I only have 2. What am I going to do? I'm going to add a 3 over here. Then 3 times 2 is 6. 6 and 6, this matches up. I know and we're almost there. Now, how many Mg? 3Mg, I have 3Mg over here. All right, this is balanced. This wasn't easy. This was a hard one, but I wanted to do a hard one. So my coefficient is 2, 3, 1, no coefficient, and 6 over here. So that was balancing chemical reaction. So practice.
9:54
Practice balancing reaction. And you are going to actually do a lot of practice because
10:01
we are going to do a lot of chemical reaction for next couple of lectures. But the key is balancing chemical reactions and balancing polyatomic ions as one unit. All right. So now, what am I going to do today? I'm going to categorize chemical reactions for you. I'm going to categorize chemical reaction reactions for you, okay? Ready for our first category? So I'm going to categorize chemical reactions for you. The first category is combination.
10:39
Combination. Now, combination is when you have A plus B goes to AB. You have A plus B, or you probably can't see that. You have A plus A goes to AB, that's a combination reaction. You combine it together. So combination reaction is A plus B going to AB. Give me an example. Here's an example. Let's say I have copper solid plus sulfur solid, goes to copper sulfide. That's a combination reaction. You're combining things together. Now, what do you think the opposite of combination is?
11:30
Every time I ask this, someone says uncombination. Uncombination is not a word. The opposite of combination would be decomposition. It's decomposition. Okay? What's decomposition? Decomposition, when you have AB going to A plus B, when you have AB going to A plus B. So you decompose. All right. Here's my favorite reaction to show. Calcium carbonate over time decomposes to calcium oxide solid, and carbon dioxide gas. it decomposes. One thing you decomposes. I like talking about this reaction.
12:17
Calcium carbonate, you've heard that word before. Statues, they used to make statues from calcium carbonate, okay? Now what happens with statues over time? What do you think? Over time, statues they get disfigured, right? And I read somewhere that in China, they spend so much money, billions and billions of dollars, to try to restore the Buddha statues. So, all the countries, they spend a lot of money trying to restore the old statues. And the reason the statues get disfigured is
12:56
because those people did not take care of [inaudible] because they used calcium carbonate to make the statues. Now what happens to calcium carbonate over time? It decomposes. Especially if you have a lot of rain, rains acidic, this is going to be happening all the time. Now here's the problem. As calcium carbonate decomposes, it forms calcium oxide and carbon dioxide gas. So this is a gas. What happens to the gas? It goes away.
13:30
The gas goes away, so you can never make this reaction to go back. So that's why statues get disfigured over time. So one day, if you get famous, and they want to make a statue of you, you're going to say, "No, I don't want calcium carbonate. Gold is the way to go." If you make your statue from gold, that's not going to get disfigured. You can't afford gold? Silver is good too, you know. We'll see, if we get that famous that they make a statue of you, you probably can afford gold or silver.
14:00
So far, so good? So, next time, you see a statue that is kind of falling apart, you'll say, "Hmm, calcium carbonate, that's what they made it from."
14:11
Okay, number three. Ready? Number three is single replacement reaction. Number three, single replacement reaction, okay? So, so far, we've done combination, decomposition, which is opposite, single replacement reaction. Yes, single replacement reaction, just like the name, basically, what's going to happen, you're going to have AB plus C. So you're going to have a couple and you're going to have a single guy, and the single guy breaks up the couple. You end up CD plus A. Yeah,
14:56
atoms have so much drama, you have no idea. So that's my single replacement reaction. To give you an example, I have zinc solid plus copper sulfate. Zinc is going to break this guy there. It will be zinc sulfate plus copper solid. Again, we are going to go over all this reaction in detail. I just wanted to give you an overview. Okay, number four. So we did single replacement reaction. The next one is double replacement, double replacement.
15:33
Now, what do you think the double replacement reaction is? Now, the single replacement reaction, you had a couple and you had a single, you have a compound, you have one male that's going to break them up. Now, for double replacement reaction, you have two compounds. What they're going to do, they're going to switch partners, okay? So what do you have? You have AB plus CD. So now you have two couples. And what's going to happen? They're going to switch partner. Again, no judgment.
16:11
Well, atoms have a lot of drama. So that's a double replacement reaction. What's going to happen is they're going to switch partner. Let me give you an example. An example would be silver nitrate plus sodium chloride. So you have two compound, they're going to switch partner. What you end up getting is silver chloride plus sodium nitrate. So far, so good? Okay. So al I'm asking you to do if you see a compound and see a reaction, be able to recognize what kind of reaction you have.
16:50
So combination, decomposition, single replacement, double replacement. Ready for last one? Okay. Our last one is combustion reaction. Our last one is combustion reaction.
17:09
So our last one, number five, is combustion reaction.
17:23
Now, combustion reaction, so our last one is combustion reaction. So combination, decomposition, and opposite single replacement, double replacement, and the last one is combination-- sorry, combustion, And in combustion, this is going on in your car as you're driving. So what we're going to have for combustion, we're going to have a hydrocarbon. I'll explain what that is in a second, you know some of it, plus oxygen, to to carbon dioxide plus water. So you're going to have a hydrocarbon.
18:02
What's a hydrocarbon? Hydrocarbon is a compound that is made of nothing but carbon and hydrogen. That's why you call it hydrocarbon. So it has same number of carbon, same number of hydrogen. So you have hydrocarbon plus O2 goes to CO2 plus H2O, and plus energy. It gives you energy. Okay, what do you put in your car? Gasoline right? So what do you think gasoline is? Hydrocarbon? Any type of fuel that you have minus the electric car, I don't know what those are,
18:40
those are different, they're hydrocarbon. So any kind of fuel that you use are hydrocarbon. It's kind of cool. So next time, instead of saying that, I'm going to go get gas, what can you say? I'm going to go and get some hydrocarbons. Don't say that. Don't talk like that people. I got to caution you just a little, but it's cool. Now, let me give you an example of combustion reaction, C3H8 plus O2 is going to give you carbon dioxide plus water.
19:19
Now this is cool, because C3H8, you guys know what that is? Barbecue. How do you make barbecue? How do you make the flame go? Propane. Propane is a hydrocarbon. So any type of fuel that you use, those are hydrocarbons. So next time, 1st of July, when you're barbecuing, what are you going to be thinking about? This is propane, this is a hydrocarbon, and this is a reaction that is going on. Kind of cool. Now, what I want you to do quickly, I want you to balance this equation, okay?
19:55
Now here's the hint for you. When you're balancing combustion reaction, balance carbon first, then balance hydrogen. The last thing that you should do is balance in oxygen. Otherwise, you're going to go crazy. So balance carbon, then hydrogen. The last thing you balance is carbon, okay? So let's do this. I have 3 carbons over there. I will add over here. So I have 3 carbons. That's good. I have 8 hydrogen. I add 4 here. So I have 8 hydrogen, okay?
20:31
Now the last thing you want to do is balancing oxygen. So 3 carbon, 3 carbon atom here. Then I had 8 hydrogen, I added a 4. 4 times 2, 8 hydrogen. Now, how many oxygen do I have here? I have 2 oxygen here. How many oxygen do I have here? Be careful.
20:51
3 times 2 is 6, 4 times 1 is 4. So I have 10 oxygen on this side. So this was 2. Now here, I have 3 times 2 is 6, and a 4 here. I have 10 oxygen over here. So 2 oxygen here, 10 oxygen here. What do I do? I add a 5 over here. Then I have 10 oxygen here. It matches oxygen over here. So far, so good. Okay. So then now we have a 5. Hopefully, you can see. I don't know if the lighting is that great. So I'm having 5O2, 3CO2 and 4 water. So balance carbon and hydrogen,
21:38
last thing you balance is balances oxygen. All right. Now the very, very last thing to talk about. So, combination, decomposition, single replacement, double replacement and combustion. There's one last thing to talk about, but I'm not going to give it number six. And that is, I'm not going to use number six,
22:01
because I'll tell you why. I want you to make a note of it, redox.
22:08
Now, redox reaction is a big umbrella. Redox reaction is a big umbrella, okay? Combination, decomposition, single replacement, and combustion, they are under redox reaction. So redox is a big umbrella. Combination, decomposition, single replacement and combustion, they're under redox. The only reaction that is not under redox is double replacement. So what are the category? Combination, decomposition, single replacement, double replacement, combustion, all of them are
22:45
on a bigger category called redox, I'm going to go over redox later, except double replacement reaction. Double replacement reaction is the only one that is your one redox. And that's the first one we're going to go over next time. So far, so good? Okay. So think about this. Until next time, everything you do, a lot of things that you do, are chemical reaction. You just don't think about it. All right, I'll see you guys next.
Here to help you learn
Sign in to keep a private conversation with your course tutor.
Ask me anything about the material…
Sign in to chat