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Types of Reactions - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

So your teacher asked you to memorize the different types of reactions and to be able to look at a reaction and predict what type of reaction it actually is. Here are some tricks really to actually help you determine that really quickly.

The first type of reaction is you're looking at this reaction, looking at number 1. You see two things and that the key thing in this one is that it's one compound there, one product. This should be a bell in your head right away. This is a synthesis reaction. I am making something. When you synthesise something you're making something. This case you're making a new compound. So we have a single product. Anytime you see a single product, in your head you should know right away, it's synthesis.

I'm not doing great quite yet on how to predict what the products are, that's going to be a different video. Right now we're just asking what type of reaction it is. Looking at the next one, we have a single reactant with the two products. Our key thing that we should be looking for is interesting, we have a single reactant. This is one reactant and notice below it's actually one reactant; this and this.

Now notice it can break up into elements, like the second one did; Aluminium and Nitrogen, or it can break down into compounds like the first one did; Nickel 2 oxide and water. It does not matter what the products are, as long as there's one single compound. And I don't even care there's a 2 here as long as there's a single reactant, one type of reactant. It is called a decomposition. You're decomposing something. So you know right away it's a single reactant. You're taking something and breaking it down into simpler forms. Again I don't care what the simpler forms are right now, but I do care this is single reactant, therefore this is decomposition. I'm decomposing.

The next type of reaction you can see, is whenever you see an element A, and a compound BY yields a compound but notice they've basically swapped partners. If you think about dancing, if you think you're at a dance. Let's pretend we're at a school dance and A is kind of dancing and jamming by himself and B and Y are a couple. Well A is going to come to BY and say, "Hey I want to cut in." Here's one thing. We want to make sure he cuts in and dances with the right partner and we'll talk about that again at a predicting products video. Nonetheless he's going to change and he's going to cut in and then he's going to dance with Y and B is going to be by himself. If you have an element and a compound yielding an element and a compound, we know right away this is single replacement; element compound combination.

So notice in the first one, Potassium is going to take the place of the Zinc these guys are going to swap places. In this case the Lead is going to swap places with the Iron. And notice they have swapped places. Initially the Potassium was single, now the Zinc is single. Initially the Iron was single, now the Lead is single. So notice they're switching places, that is called a single replacement.

Something similar is number 4 and this is when if two compounds yielding two compounds. If you notice and all these are going to be ionic compounds. So if you again think about that dance scenario. You're at a school dance and you have A and X dancing and B and Y are dancing. What's going to happen is, they're going to just switch partners. So A is now going to dance with Y and B is now going to dance with X. All they're doing is switching partners. So sodium is originally with Hydroxide, Copper is originally with Chloride, now these two are going to dance together and these two are going to dance together. So notice our products. Same thing here Aluminium and Hydrogen are going to switch partners. So now Aluminium is going to dance with Sulphate and Hydrogen is going to dance with Nitrate, notice our products here.

We call this instead of single replacement, we're calling it double replacement. It's when two compounds switch partners.

And the last type of reaction is anything that reacts with Oxygen. If you see Oxygen in the reactants side, most likely it's going to be, well actually almost all the time, it's going to be this type of reaction. It's actually a combustion reaction. When you think of combustion reaction you think of heat. They're very exothermic, just a side note, meaning they give off a lot of heat.

Combustion reactions react with Oxygen gas. Notice, we have this Hydrocarbon Methane reacting with Oxygen. Anytime you have a Hydrocarbon reacting with Oxygen, you're always going to get these products. This being there, those products CO2 and H2O should also be very big indicator that it's combustion reaction. Even if I had a different Hydrocarbon, let's say I had C2H6, this would also be CO2 plus H2O, but that's for another video.

But also it doesn't have to be a Hydrocarbon, Magnesium when it reacts with Oxygen gives Magnesium Oxide. This being here tells me it's combustion reaction. It also finds itself in another category. What other type of reaction is this? One it's combustion, because it's reacting with Oxygen gas, but it also falls in the category of synthesis. How did I know that? It has a single product.

Just because something is in one category, doesn't mean it can't be in another category. But most likely it's only going to be combustion and synthesis, it's the only two that actually can overlap. Anytime you see O2, know it's combustion but also it might be synthesis. Anytime you see CO2 and H2O it's always; I can't emphasize enough, it's always combustion.

These are the five different types of reactions you'll see in class. Redox reactions are something completely different; if your teacher is talking about that, but it falls into these categories as well. We'll talk about that another time too. But these are the main five types of reactions; Synthesis, decomposition, single replacement, double replacement and combustion. Hope these hints helps you determine what type of reaction is what.