Now in this video we're going to talk about how to identify the different types of chemical reactions. So the first type of chemical reaction that you need to be familiar with is something called a combustion reaction. In a combustion reaction, something is typically burning and it releases a lot of heat energy.
So for example, let's say if we react... Octane, which can be found in gasoline with oxygen. Octane produces carbon dioxide and water when it reacts with air.
Now, CO2 is a gas. Water, it's a gas at high temperature. At normal temperatures, it's a liquid, but because in a combustion reaction, a lot of heat is being generated, typically water is going to be in a vapor phase.
So this reaction generates a lot of heat and also produce a lot of gas molecules which expand at high temperature and all that energy can be used to move pistons and can drive a car forward. And so combustion reactions are very useful for generating a lot of heat. Here's another example of a combustion reaction.
Let's say if we react ethanol which is found in alcohol products. If we react with oxygen, it's going to produce the same thing, carbon dioxide and water. So you can easily identify a combustion reaction just by looking at the products. If you see CO2 and water as products, you know it's a combustion reaction.
On the left, typically you'll have a hydrocarbon, which is a molecule made up of carbon and hydrogen, or sometimes there might be some oxygen there too. But the end result is the same. You have some hydrocarbon reacting with the oxygen gas in air, and it produces carbon dioxide and water.
So those are the main features of a combustion reaction. The next kind of reaction that you need to know is known as a synthesis reaction. also called a combination reaction. So what are some features of this reaction? How can we identify it?
In a synthesis reaction or combination reaction, typically you're combining two smaller things to make something larger. It can be an element reacting with another element to produce a compound. Or you can have two compounds coming together to form a large compound.
But the idea is you're taking two small things and combining them into something larger. And so you're producing something, you're synthesizing it. Well, basically you're just combining A and B to make AB.
And that way you can see it's a combination reaction. Either case, you're building something more complex. So what are some examples of a combination reaction?
Let's say if you're reacting magnesium with oxygen gas. This will create magnesium oxide. So here we have a pure element, magnesium, reacting with another pure element to make a compound.
So that's one example. Now these reactions are unbalanced. I'm not going to focus on balancing the reactions.
I want to focus on identifying the type of reaction. So as you'll see, I'm not going to balance the majority of these reactions. Another example of a synthesis reaction is this one.
Let's say if we have magnesium oxide and we react it with carbon dioxide gas. Magnesium oxide is a solid, by the way, and the same is true for magnesium metal. They're solids. So if you react a metal oxide like magnesium oxide with carbon dioxide, it could form into another larger compound, magnesium carbonate. Both examples are synthesis reactions.
So here we have a small compound reacting with another small compound to form a more complex, larger compound. So that's a combination reaction. The next type of reaction that we need to talk about is called decomposition. So when you hear the word decomposition, what do you think of? A decomposition reaction is simply the reverse of a synthesis or combination reaction.
You're decomposing, you're taking something larger or complex and breaking it down into smaller components. So let's say if you have a product, or I mean a reactant, AB, you're going to break it down into A plus B. In a synthesis reaction...
It's the opposite of that. In the synthesis, you want to combine A and B to form a larger compound, AB. So, just think of a decomposition as the reverse of a synthesis or a combination reaction. So, what are some examples of a decomposition reaction?
Now, we talked about forming magnesium carbonate, but it turns out that... If you have a metal carbonate and if you add a heat to it, you can get the metal oxide back. Heat will cause the volatile element, which is CO2, it's going to cause the volatile component of magnesium carbonate to escape into the air. So when you add heat, you're going to cause the gas to leave the magnesium carbonate system.
So heat will drive away CO2. Here's another example. Let's say if you have mercury oxide, and if you add heat to it, any volatile component in this compound will leave. So this will create liquid mercury, which is a metal, and it's going to generate oxygen gas, which is going to leave, especially if you heat it up too.
Another example of a decomposition reaction. is water. If you add electricity to water, if you run an electric current through it, it can decompose into hydrogen gas and oxygen gas. So that's the decomposition reaction.
So in a decomposition reaction, you could take a complex compound and break it up into two smaller compounds, or you can take a compound and decompose it into two simpler elements. So that's a decomposition reaction, and here is the general equation for it. AB turns into A plus B. Now let's say if we have a metal hydroxide.
In this case, calcium hydroxide. What do you think is going to happen if we add heat to it? If you add heat to calcium hydroxide, very similar to magnesium carbonate, Anything that's volatile will leave the reactant.
This is going to produce calcium oxide and water vapor. If the temperature is higher than 100 degrees Celsius, water is going to be in its vapor form. It's going to be a gas. If it's lower than 100, then it could still be in its liquid form. So let's say we have the reverse reaction.
If we react magnesium oxide with water. This can produce magnesium hydroxide. Now which one is, rather, what kind of reactions do we have here?
The first one, is it a combustion reaction? Is it a synthesis reaction? Or is it a decomposition reaction?
So the first one, we can call this AB and it turns into A plus B. So therefore, this is a decomposition reaction. Now looking at the second example, we have two compounds turning into a larger compound.
And that's the general structure of a synthesis or a combination reaction. So the first reaction is a decomposition, and the second reaction where magnesium oxide reacts with water to produce magnesium hydroxide, that's a synthesis reaction. Now the next type of reaction that we need to talk about is the single replacement reaction.
This is also known as a single displacement reaction. So here's the general equation for this reaction. A reacts with B plus C.
So A is a pure element and reacts with a compound, BC. And typically, A is going to pair up with either B or C. If it pairs up with C, it's going to kick B out of the solution. So now B is a pure element by itself, and AC is within a compound. So that's the general formula for a single replacement reaction.
So what are some examples of this? Let's say if we have zinc metal reacting with a solution of copper chloride, which is going to be in the aqueous state. So, Zinc Metal is going to replace... the copper metal in the solution.
So zinc is not in the solution, it's in its metallic form. Copper is in the solution. So zinc is going to go into the solution and kick out copper, which means zinc is going to trade places with the copper. So zinc is going to pair up with chlorine and copper has been kicked out. So now copper is in its solid metallic form, while zinc chloride is now dissolved into the solution.
So that's an example of a single replacement reaction. Typically, a metal displaces another metal in a solution. Sometimes it could be a nonmetal displacing another nonmetal in a solution.
So here's an example. Let's say if we have elemental bromine, which is a liquid in its natural state, and it reacts with aqueous sodium iodide. In this example, bromine is going to pair up with sodium.
So it's going to displace iodide out of the solution. So you're going to have sodium bromide in the solution and elemental iodine out of the solution. I2 is a solid at room temperature.
Sometimes a metal can replace another non-metal, in this case hydrogen. So for example, let's say if we have a metal like... Fe it can displace the hydrogen in hydrochloric acid so Fe is going to pair up with Cl And it's going to form Fe Cl2 Which is an aqueous state and it's going to displace hydrogen so this is one of those rare examples where a metal displaces a nonmetal but for the most part metals tend to replace metals and nonmetals tend to displace other nonmetals. Now let's move on to a double replacement reaction. In a double replacement reaction, also known as a double displacement reaction, it differs from a single replacement reaction by this one key fact.
In a single replacement reaction, an element usually reacts with a compound. So for example, A, the element, reacts with the compound BC. But in a double replacement reaction, the compound AB reacts with another compound, CD.
Now A is going to pair up with D, and B pairs up with C. So it's a double replacement. So we're going to have AD plus BC.
And so that's the general formula of a double replacement reaction. Now there's different types of double replacement reactions. You have precipitation reactions, you have acid-base neutralization reactions, gas evolution reactions, just to name a few.
So for example, let's say if we're reacting with silver nitrate, which is in the aqueous phase, that means it's soluble in water, it dissolves in water. And let's mix it with... sodium chloride, which also dissolves in water.
So that's an aqueous phase. If we want to draw the products of this reaction, silver is going to pair up with chloride and it's going to form silver chloride, which is a white insoluble product. So it's a solid. Silver chloride is an ionic compound that doesn't dissolve in water.
It's insoluble. Sodium chloride on the other hand is a soluble compound. It dissolves in water, so we write aqueous. Sodium is going to pair up with nitrate, and you're going to get sodium nitrate, NaNO3, which is also soluble in water.
So this is going to be in the aqueous phase. So this whole thing is known as a double replacement reaction. But when you mix two aqueous solutions, and if you get a solid product, This double replacement reaction now has another name.
It's called a precipitation reaction. So by mixing two aqueous solutions, these could be two clear solutions, and if you get a solid product that forms, and if you can see the solid product in the solution, then you have a precipitation reaction. Now here's another example. Let's say if we mix hydrochloric acid. which is an aqueous phase with sodium hydroxide.
What's going to happen? As you can see, we have a double replacement reaction. We have a compound reacting with another compound.
Hydrogen is going to pair up with hydroxide to form water. And water is in a liquid phase. Sodium.
is going to pair up with chlorine and you're going to get sodium chloride, which is going to be in the aqueous phase. So this double replacement reaction has another name. HDL is an acid, it's hydrochloric acid. Sodium hydroxide is a base. When you mix a strong acid with a strong base, you're going to get salt and water.
Sodium chloride is found in table salt. This is known as a neutralization reaction, particularly an acid-base neutralization reaction. You mix in two aqueous solutions, one is an acid, one is a base, and you get a neutral water and salt.
So that type of double replacement reaction is an acid-base neutralization reaction. So what about this one? Sodium sulfide in the aqueous state reacts with hydrochloric acid, which is also in the aqueous state.
And it's going to produce, so sodium is going to pair up with chlorine to make sodium chloride, which is also in the aqueous state. And then hydrogen is going to react with sulfide to produce H2S. Hydrosulfuric acid is a gas.
So this particular type of double replacement reaction, when you mix two aqueous solution and you get a gas, is known as a gas evolution reaction. So that's another type you need to be familiar with. Now what about this one? Let's say if we have sodium chloride in the aqueous phase, and let's say it reacts with potassium nitrate in the aqueous phase. Now this is another double replacement reaction.
We have a compound reacting with a compound. To draw the products, sodium is going to pair up with nitrate, and it's going to form sodium nitrate, which is also soluble. And potassium is going to pair up with chlorine, or chloride, forming casein, which dissolves in water.
So we mix two aqueous solutions, and we've still got aqueous products. Even though this is a double replacement reaction, No reaction actually takes place. There's no change in phase. The only way a reaction takes place is if you get a solid product, a liquid product, or a gaseous product.
If everything remains in the aqueous phase, no reaction took place. So now let's take a brief quiz. I'm going to write down a few reactions and I want you to classify each reaction based on the names that we've went over so far. So here's the first one. Let's say if calcium hydroxide is exposed to a heat source.
and produces calcium oxide and water what kind of reaction is this is this a single replacement double replacement is it a combination reaction decomposition reaction is it a combustion reaction which one is it So we have a complex compound on the left and we're breaking it down into two smaller compounds. So this is known as a decomposition reaction. So now let's move on to the next question. So let's say zinc metal reacts with aqueous nickel chloride. to produce Zinc chloride and nickel metal.
What type of reaction do we have here? So an element, a pure element, reacts with a compound to produce another compound and a pure element. This is known as a single replacement reaction. Zinc replaced nickel in the reaction, so only one replacement actually took place. Here's another one.
Barium oxide reacts with carbon dioxide to produce barium carbonate. So what type of reaction do we have here? So we have two compounds joining up together to form a larger compound. This is known as a synthesis reaction or a combination reaction.
So that's the answer for that one. Now what about when hydrogen peroxide converts into hydrogen gas and oxygen gas? What kind of reaction do we have here?
So we have a compound breaking down into two pure elements. This is called a decomposition reaction. By the way, hydrogen peroxide will naturally do this. If it's exposed to air and sunlight, it can naturally break down into hydrogen gas and oxygen gas.
Try this one. Lead nitrate, or rather lead 2 nitrate, reacts with sodium chloride to produce lead 2 chloride and Sodium Nitrate. Lead Nitrate is soluble. It's in the aqueous phase and the same is true for Sodium Chloride and Sodium Nitrate. Lead Chloride doesn't dissolve in water.
It's insoluble. So what we have here is two aqueous solutions mixed into form a solid product. So notice that lead paired up with chlorine to form lead chloride. Nitrate paired up with sodium to form sodium nitrate.
So this is a double replacement reaction. In this example, lead replaced nitrate to pair up with chlorine. and sodium replaced chlorine to pair up with nitrate.
So we have a double replacement going on here. And as we can see, you can also see it this way. We have a compound, AB, which is lead nitrate. It reacts with another compound, CD, that's sodium chloride, to produce. So A got together with D to form AD, that's lead chloride.
The two in the middle B and C got together to form B C or in this case actually CB Where C is for sodium? And so whenever you see that general reaction, you know it's a double replacement reaction, or you can call it a double displacement reaction if your textbook uses that term. So that's a quick way to identify it.
You have a compound reacting with another compound. Now, there's another name for this double replacement reaction. Whenever you mix two aqueous solutions, and if you get a solid product that forms, This double replacement reaction is also called a precipitation reaction. So that's another name for it.
Now what about this reaction? Chlorine reacts with sodium bromide to form sodium chloride and bromine. Chlorine is a gas. Bromine is a red liquid. Sodium bromide and sodium chloride dissolve in the solution.
What kind of reaction do we have here? So we have a pure element which is chlorine and it reacts with a compound sodium bromide. When you see that you know it's a single replacement reaction.
By the way, all single replacement reactions are redox reactions, and all combustion reactions are redox reactions. A redox reaction is a reaction where you have a transfer of electrons. You have oxidation, which is a loss of electrons.
and reduction, which is the gain of electrons. We won't go into it much, but I just want to let you know that all single replacement reactions are redox, and all combustion reactions are redox. A double replacement reaction is never a redox reaction. Now, as for decomposition reactions and synthesis reactions, if you have, let's say, in a decomposition reaction, a compound break it down into pure elements, then it's a redox reaction. And the reverse is true.
In a synthesis reaction, if you have two pure elements combined to form a compound, it's a redox reaction. Now, if you have a large compound breaking into two smaller compounds in a decomposition reaction, chances are it's probably not a redox reaction. And the reverse is true for a combination reaction.
If you have two smaller compounds reacting to form a larger compound, chances are it's not a redox reaction. So that's for those of you who are also studying redox reactions, if you need to know that. So now let's get back to this, A plus BC.
So A is going to pair up with C. In this case, rather, A pairs up with B. B is sodium and A is chlorine, so here we have BA. and then see it by itself.
So in this example we have a nonmetal displacing another nonmetal in the solution. So chlorine displaces bromine, and chlorine pairs up with sodium to form sodium chloride. So that's a single replacement reaction.
Now what about this one? Methane, also known as natural gas, reacts with oxygen gas to produce carbon dioxide and water. What type of reaction do we have here?
Anytime you see CO2 and water, and if you have a hydrocarbon on the left, this is a combustion reaction, which is also a redox reaction. Now what about this one? Potassium chlorate is exposed to heat, and then it forms potassium chloride. and oxygen gas. What type of reaction do we have?
So here we have a complex compound, AB, and upon heating it, it breaks down to two smaller compounds, A and B. But in this case, B is a pure element and A is a compound. So this type of reaction is also a redox reaction. Anytime you can produce a pure element from a compound, it's going to be a redox reaction.
But this particularly, the name that we're looking for, is a decomposition reaction. We're taking a complex compound and we're breaking it down to two smaller components, A and B. So potassium chlorate is undergoing thermodecomposition to produce oxygen gas and potassium chloride. Now what about this one? Sulfuric acid reacts with potassium hydroxide to produce water and sodium sulfate.
So what kind of reaction do we have here? Sulfuric acid is in the aqueous phase, and the same is true for potassium hydroxide. They dissolve in water, and water is in the liquid phase. Sodium sulfate is soluble.
It dissolves in water, so it's in the aqueous phase. Sulfuric acid is a compound, AB. Potassium hydroxide is also a compound.
So we have two compounds reacting with each other. This is called a double replacement reaction. Whenever you have two compounds reacting with each other, it's a good indication that you have a double replacement reaction.
So in this example, we can see that hydrogen paired up with hydroxide to produce water. So that's A. Getting together with D to form AD.
And then potassium pairs up with sulfate. And for some reason I wrote sodium sulfate, so that's my mistake. That was supposed to be potassium sulfate. Let me just put that here.
K2SO4. That's what the product should have been. But it's still a double replacement reaction.
And so C... pairs up with B. producing CB. Now there's another name for this type of reaction, in addition to being called a double replacement reaction. Sulfuric acid is a strong acid.
Potassium hydroxide is a strong base. These two are getting together to form salt, which is potassium sulfate. It's a type of salt.
Almost all ionic compounds are considered salts. So it's producing salt and water. So this is called acid-base neutralization reaction.
So when you mix two aqueous solutions and if you get a liquid product and if this is an acid and this is a base then typically it's going to be an acid-base neutralization reaction. Now let's move on to our next example. Magnesium metal reacts with nitrogen gas in the air to form magnesium nitride.
Perhaps you perform this experiment in class. If you take a strip of magnesium metal or one of those magnesium ribbons, if you burn it in air, it produces this very, very bright, brilliant light. You got to be careful because ultraviolet light also is produced from it.
And this is the reaction that's happening. When you burn magnesium metal in air, you're burning magnesium nitride. it can react with the nitrogen gas in air and so it produces magnesium nitride.
So this type of reaction, how would you classify it? So we have a pure element, magnesium, reacting with another pure element, nitrogen gas, to produce a compound. So we have two small things combining to form something that's larger or more complex.
So this is called a synthesis reaction, also known as a combination reaction. By the way, this particular reaction, is it a redox reaction? Here's a quick and simple technique to know if you have an oxidation reduction reaction, also known as a redox reaction. If you see a pure element on one side, and that same element inside of a compound, then for the most part... It's a redox reaction.
So this particular type of synthesis reaction is an oxidation reduction reaction. But the answer we'll focus on today is the synthesis reaction or combination reaction. Now let's say if we have pentane, C5H12, and we react it with oxygen gas in the air, and it produces carbon dioxide. and water. So what kind of reaction do we have?
Pentane is a liquid and oxygen, CO2, and water will be in the gaseous state. This reaction releases a lot of energy and so water will most likely be in the vapor phase. So what kind of reaction do we have? So anytime you have a hydrocarbon on the left and if you produce CO2 and water on the right, then you know you have a combustion reaction. So that's the answer.
Now is this reaction a redox reaction? Is there a transfer of electrons taking place in this reaction? Notice that oxygen is in its elemental form on the left side.
On the right side it's found within the compound. So just by looking at this you can see that this is also a redox reaction. It's an oxidation reduction reaction.
So all combustion reactions are redox reactions. Now what about this one? Let's say if we have sulfurous acid and upon heating it, it turns into liquid water and sulfur dioxide which is a nonmetal oxide. and it's also a gas and this is an aqueous phase.
What kind of reaction do we have here? So this is a decomposition reaction. So we have a complex compound AB and it's breaking down into two smaller compounds.
So it's a decomp reaction. Now this particular decomposition reaction Is it a redox reaction? Notice that we have no pure elements. on any side of the reaction. All the elements are in the form of a compound.
And when you see this, typically, this is not a redox reaction. If there's no pure elements anywhere, chances are it's not a redox. Now let's move on to our next example.
We're going to react sodium bicarbonate with hydrochloric acid and in this reaction we're going to get sodium chloride, water, and CO2. So these two are in the aqueous phase. Water is in the liquid phase and CO2 is in the gas phase. So how would you classify this reaction?
And have you seen anything like this? It turns out that there's multiple classifications for this reaction, because there's a lot that's happening. First and foremost, we're mixed in two aqueous solutions, and we are getting a gaseous product. When you see that, you can classify it as a gas evolution reaction. At the same time, sodium bicarbonate...
can act as a weak base and hydrochloric acid is a strong acid and we do get water which is a feature of an acid-base neutralization reaction. Now before we get water and carbon dioxide we get something else. So when we react sodium bicarbonate which is also called sodium hydrogen carbonate with HDL Initially, you could think of this as a double replacement reaction.
Sodium is going to pair up with chlorine to form sodium chloride. And hydrogen pairs up with HCO3 bicarbonate to produce carbonic acid. So if you view it this way, this appears to be a double replacement reaction.
I wrote that wrong. AB reacts with CD to produce. AD and CB.
So the first step is a double replacement reaction. Now the second step, carbonic acid, it's unstable. It's an intermediate and it breaks down into water and carbon dioxide.
The two things that we see here. So the second step is a decomposition reaction. But overall, you can think of it as a gas evolution reaction because we do get a gas by mixing two aqueous solutions.
So as you can see, there's multiple classifications for this type of reaction. It's a complex reaction. Now let's review the main types of reactions that we've run over so far.
So if you have a compound AB and you break it up into two smaller components, this is known as a decomposition reaction. So I'm going to write decomp for short. Now the reverse of a decomposition reaction, let's say if you mix two smaller components and get a larger component, this is known as a synthesis reaction, or you can call it a combination reaction.
If you react an element with a compound, Then these two will switch places. A is going to pair up with C, kick out B. This is known as a single replacement reaction. And if you react two compounds together, this is called a double replacement reaction. And there's three types of double replacement reactions.
You have precipitation reactions, which occur when mixed in two aqueous solutions to form a solid product. You have an acid-base neutralization reaction, when you mix an acid and base, you get liquid water and a salt. And then you have the gas evolution reactions, where you mix two aqueous solutions and you get a gaseous product. And finally, combustion.
So typically you'll have some hydrocarbon and may have oxygen within. It reacts with oxygen in the air to produce CO2 and water. So that's a combustion reaction. So those are the main types of reactions that you need to be aware of. Thanks for watching.