Types of chemical reactions
AB -> A + B
decomposition
Single replacement reaction aka single displacement reaction
A + BC -> AC + B So A is a pure element and it reacts with a compound BC and typically A will pair up with either B or C. If it pairs up with C, it will kick B out of the solution. So now B is a pure element by itself and AC is a compound. What are some examples? Let's say if we have zinc metal reacting with a solution of copper chloride which is going to be in aqueous state. Zinc metal will replace copper. Zinc will enter solution and kick out copper will pair up with chlorine. So now Cu in solid metallic form while zinc dissolved in solution of zinc chloride. Zn(s) + CuCl2 (aq)-> ZnCl2 (aq) + Cu(s) Typically a metal displaces another metal in a solution. Sometimes it can be a nonmetal displacing another nonmetal in a solution. 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 is going to displace iodide out of the solution. So you will have bromine in a solution and elemental iodide outside of solution. At room temp I2 is a solid. Br2(l) + NaI(aq) -> NaBr(aq) + I2(s) Sometimes a metal can replace a nonmetal for in this case hydrogen. Let's say we have a metal like Fe. Fe can displace the hydrogen in hydrochloric acid. So Fe is going to pair up with Cl and it is going to form FeCl2 which is an aqueous state. It will displace H. This is one of those rare instances where a metal displaces a nonmetal but for the most part metals displace metals and non-metals displace non-metals. Fe(s) + HCl(aq) -> FeCl2(aq) + H2(g)
Zn(s) + NiCl2(aq) -> ZnCl2(aq) + Ni(s)
A pure element reacts with a compound to produce another compound and a pure element. This is a single replacement reaction.
Cl2(g) + NaBr(aq) ---> NaCl(aq) + Br2(l)
Br2 is red liquid We have a pure element, chlorine, it reacts with solid compound when you see that you know that it is a single replacement reaction. By the way, all single replacement reactions are redox reactions. Also, 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 you have reduction which is a gain of electrons. A double replacement reaction is never a redox reaction. As for decomp and synthesis... if you have, let's say, in a decomp reaction a compound breaking down into pure elements, then it is a redox reaction and the reverse is true too in a synthesis reaction if you have two pure elements combining to form a compound it is a redox reaction. Now, if you have a large compound breaking into two smaller compounds in a decomposition reaction, chances are it is probably not a redox reaction. The reverse is true for a combination reaction. If you have two smaller compounds reacting to form a larger compound, chances are it is not a redox reaction. Back to this- so A + BC, A pairs up with C, in this case A pairs with B, B is sodium A is chlorine C is by itself. We have a non-metal displacing another non-metal in a solution. So chlorine displaces bromine. And chlorine pairs up with sodium to form sodium chloride.
Double replacement reaction aka double displacement reaction
Differs from a single replacement reaction by one key fact. In a single replacement reaction, an element usually reacts with a compound. For example A reacts with compound BC. But in a double replacement reaction compound AB reacts with another compound CD. A pairs up with D and B with C, so double displacement. AB + CD -> AD + BC There are different kinds 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 are reacting with silver nitrate which is in aqueous phase, that means that it is soluble in water, it dissolves in water, and let's mix it with sodium chloride which also dissolves in water so is aq phase. Silver will pair with chloride forming silver chloride- a white, insoluble product, so it is a solid. Sodium chloride on the other hand does dissolve in water that is why it is aqueous. Sodium is going to pair with nitrate and you will get sodium nitrate which is aqueous/soluble in water. AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq) So this is known as a double displacement reaction, but when you mix two aqueous solutions, and if you get a solid product, this double displacement reaction now has another name, it is called a precipitation reaction. So you mix two aqueous/clear solutions and a solid forms, then you have a precipitation reaction. Let's say you mix hydrochloric acid which is in aqueous phase, with sodium hydroxide, what is going to happen? As you can see we have a double displacement reaction. We have a compound reacting with another compound. Hydrogen will pair up with hydroxide to form water and water is in a liquid phase. Sodium will pair up with chlorine and we get sodium chloride which will be in aqueous phase. So this double displacement reaction has another name. HCl is an acid- hydrochloric acid. Sodium hydroxide is a base. When you mix a strong acid with a strong base, you will get salt and water. Sodium chloride is found in table salt. This is known as an acid base neutralization reaction. You're mixing two aqueous solutions: one is an acid one is a base, and you get a neutral water and salt. HCl(aq) + NaOH(aq) -> H2O(l) + NaCl(aq) Sodium sulfide in the aqueous state reacts with hydrochloric acid also in aqueous state and it is going to produce... sodium pairs up with chlorine to make sodium chloride which is also in 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 solutions and you get a gas, is known as a gas evolution reaction. Na2S(aq) + HCl (aq)-> NaCl(aq) + H2S(g) Let's say we have sodium chloride, in the aqueous phase, and it reacts with potassium nitrate in the aqueous phase. This is another double replacement reaction, we have a compound reacting with a compound. Sodium will pair up with nitrate, and it is going to form sodium nitrate which is also soluble. Potassium pairs with chlorine forming KCl which dissolves in water. We mixed two aqueous solutions and still got aqueous products. Even though this is a double replacement reaction, no reaction actually takes place. There is no change in phase. The only way that 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. NaCl(aq) + KNO3(aq) -> NaNO3(aq) + KCl(aq)
Mg(s) + N2(g) -> Mg3N2(s)
If you burn a magnesium ribbon in air it produces this really bright light. You have to be careful. This is the reaction happening when you burn magnesium in air it will react with N in air. Two pure elements combine to form compound. This is called a synthesis reaction aka a combination reaction. This particular reaction is a redox reaction. So, if you see a pure element on one side, and that same element inside a compound, for the most part it's a redox reaction.
Combustion reaction
In a combustion reaction something is typically burning and it releases a lot of heat energy. So for example let's say we react octane (found in gasoline) with oxygen. Octane produces CO2 and water when it reacts with ai. C8H8(l) + O2(g)-> CO2(g) + H2O(g) CO2 is a gas, water is a gas at high temp. At normal temp it is 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 produces a lot of gas molecules which expand at high temp and all that energy can be used to drive pistons and to drive a car forward. So combustion reactions are very useful for generating a lot of heat. Let's say if we react ethanol, which is found in alcohol products, if we react it 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 its products. If you see CO2 and water as its products you know that it is a combustion reaction. On the left typically you will have a hydrocarbon which is a molecule made up of hydrogen and carbon but sometime there might be some oxygen there too. But the end result is the same- you have some hydrocarbon reacting with oxygen gas and it produces carbon dioxide and water.
Mini quiz
Let's say we have a metal hydroxide in this case calcium hydroxide. What do you think will happen if we add heat to it? If you add heat to calcium hydroxide, very similar to magnesium carbonate, anything that is volatile will leave the reactant. This is going to produce calcium oxide and water vapor. Ca(OH)2(s) -heat--> CaO(s) + H2O(g) If the temp is higher than 100 degrees celsius water is going to be in vapor form- a gas. If lower than 100 it will be in liquid form. Let's say we have reverse reaction- we react magnesium oxide with water this can produce magnesium hydroxide. MgO(s) + H2O -> Mg(OH)2 What kinds of reactions do we have? First one is AB -> A + B therefore decomp reaction Second one we have two compounds turning into a larger compound therefore synthesis/combination
CH4 + O2 -> CO2(g) + H2O(g)
Methane aka natural gas Any time you see CO2 and water, and you have a hydrocarbon on the left, this is a combustion reaction aka redox reaction.
Pb(NO3)2(aq) + NaCl (aq)-> PbCl2(s) + NaNO3(aq)
Notice that lead paired with chlorine to form lead (II) chloride. Nitrate paired up with sodium to form sodium nitrate. This is a double displacement reaction. Lead replaced nitrate to pair up with chlorine. Sodium replaced chlorine to pair up with nitrate. We have a double replacement. We have 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.
KClO3-heat->KCl + O2
So here we have a complex compound, AB, and upon heating it it breaks down into two smaller compounds A and B. In this case B is a pure element and A is a compound. This type of reaction is also a redox reaction. Any time you can produce a pure element from a compound, it is going to be a redox reaction. Particularly the name we are looking for is a decomposition reaction. We are taking a complex compound and breaking it down into two smaller points: A and B. Potassium chlorate is undergoing thermal decomposition to produce oxygen gas and potassium chloride.
NaHCO3(aq) + HCl(aq) -> NaCl(aq) + H2O(l) + CO2(g)
Sodium bicarb It turns out that there are multiple classifications for this reaction because there is a lot that is happening. First and foremost, we are mixing two aqueous solutions and 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 HCl, initially you can 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. NaHCO3 + HCl -> NaCl + H2CO3 So if you view it this way, this appears to be a double replacement reaction. So the first step is a double replacement reaction. Now the second step carbonic acid it is unstable, an intermediate, so it breaks down into water and carbon dioxide. So the second step is a decomposition reaction. But overall you could think of this as a gas evolution reaction because you do get a gas by mixing two aqueous solutions.
H2SO4(aq) + KOH(aq) -> H2O(l) + K2SO4(aq)
Sulfuric acid Sulfuric acid is a compound, potassium hydroxide is also a compound, we have two compounds reacting with each other. This is called a double replacement reaction. Hydrogen paired up with hydroxide to produce water. Then, potassium pairs up with sulfate. There is another name for this type of reaction in addition to being called a double displacement 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, almost all ionic compounds are considered salts, so it is producing salt and water. So this is called an acid base neutralization reaction. So when you mix two aqueous solutions, and you get a liquid product, and this is an acid and this is a base, then typically it is going to be an acid base neutralization reaction.
H2SO3(aq) -heat-> H2O(l) + SO2(g)
Sulfurous acid Sulfur dioxide is a non-metal oxide Decomposition reaction. We have a complex compound and it is breaking down into two smaller compounds. Is this a redox reaction? Notice that we have no pure elements on either side of the reaction. All the elements are in the form of a compound and when you see that is usually not a redox reaction. If there are no pure elements anywhere, chances are is not a redox reaction.
BaO(s) + CO2(g) -> BaCO3(s)
Two compounds combine to make a more complex compound. This is known as a synthesis or combination reaction.
Ca(OH)2(s) --heat-->CaO(s) + H2O(g)
We have a complex compound that we are breaking down into two smaller compounds, so this is a decomposition reaction.
Synthesis reaction aka combination reaction
What are some features of this reaction. In this reaction typically you're combining two smaller things to make something larger. It could be an element reacting with another element to produce a compound. Or you could have two compounds that form a larger compound. A + B -> AB Examples (not balanced): Mg(s) + O2(g) -> MgO(s) Magnesium plus oxygen gas will create magnesium oxide. Here you have a pure element, oxygen, combining with another pure element, magnesium, to form a compound. MgO(s) + CO2(g) -> MgCO3(s) So if you react a metal oxide like magnesium oxide with carbon dioxide, it could form into another larger compound, magnesium carbonate.
CxHy + O2 --> CO2 + H2O
You have some hydrocarbon, may have oxygen, reacts with oxygen in the air to produce CO2 and H2O. Combustion.
AB + CD --> AD + CB
double replacement 3 types: 1. precipitation- 2 aqueous solutions react to form solid product 2. acid base neutralization reaction- you mix acid and a base and you get liquid water and salt 3. gas evolution reaction- you mix two aqueous solutions and you get a gaseous product
H2O2 -> H2 + O2
hydrogen peroxide converts to hydrogen gas and oxygen gas We have a compound breaking down into two pure elements. This is called a decomposition reaction.
C5H12(l) + O2(g) -> CO2(g) + H2O(g)
pentane This reaction releases a lot of energy, so water most likely will be in vapor phase. Any time you have a hydrocarbon on the left, and you produce CO2 and water on the right, then you know that you have a combustion reaction. is this a redox reaction? Is there a transfer of electrons taking place? Notice that oxygen is in its elemental form on the left side, but on the right side it is found in a compound, so just by looking at that you can see that this is also a redox reaction. All combustion reactions are redox reactions.
decomposition reaction
reverse of synthesis or combination reaction. You're taking something larger/more complex and breaking it down into smaller components. AB -> A + B We talked about forming magnesium carbonate. But it turns out that if you ahve a metal carbonate and you add heat to it, you can get the metal oxide back. Heat will cause the volatile component (CO2) of mag carbonate to escape into the air. Heat will drive away CO2. MgCO3(s) --heat--> MgO(s) + CO2(g) Let's say you have mercury oxide. 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 will generate oxygen gas which is going to leave, especially if you heat it up too. HgO(s) --heat--> Hg(l) + O2(g) If you add electricity to water, if you run an electric current thru it, it can decompose into hydrogen gas and oxygen gas. H2O--electricity--> H2(g) + O2(g) So in a decomposition reaction you can 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.
A + BC -> AC + B
single replacement
A + B -> AB
synthesis