Reactions

__ **Types of Chemical Reactions** __
Synthesis Reaction

A synthesis reaction is defined as the combining of 2 or more elements/compounds to form a single compound.

A + B -->C

In this cartoon the skinny bird (reactant) and the worm (reactant) combine to make a product, the fat bird.

Common Synthesis reaction · Element + Element --> Compound · Metal oxide + Water --> Metallic Hydroxide (base) · Non metal oxide + Water --> Non binary acid · Metal oxide + Non Metal oxide --> Non binary Salt But others types of synthesis reactions include: · Metal + Non metal --> Ionic compound

**Decomposition Reaction**

A Decomposition Reaction is defined as the breaking down of a single compound into 2 or more compounds/Elements. Decomposition reactions are the reverse of Synthesis reactions, so they work both ways.

C --> B + A

In this cartoon the egg (reactant) which contained the turtle at one time, cracked open and the turtle (product) and eggshell (product) are now two separate substances.

· Common Decomposition Reaction · Binary compound --> Element + Element · Metallic Hydroxide --> Metal oxide + Water · Non Binary Acid --> Non Metal oxide + Water · Non Binary Salt --> Metal oxide + Non Metal oxide · Metallic Chlorates --> Metallic Chlorides + Oxygen · Hydrogen Peroxide --> water + Oxygen · Metallic Carbonate --> Metal oxides + Carbon dioxide

**Single Displacement Reaction**

A single displacement reaction is a displacement of an element in a compound. Element + Compound --> Compound + Element



In this cartoon The Guy in the orange shirt steals the other guys date at the dance. So apart of one of the reactants trades places and is in a different place among the products.

Type 1 Single Displacement reactions with Metals/ Hydrogen BC + A --> AC + B  Element A has replaced B (in the compound BC) to form a new compound AC and the free element A. Remember that B and A are both cations (positively-charged ions) in this example. A forms a cation ( A is a metal).

In order for a single displacement reaction to happen it must be more active than the metal it is set to replace. In order to determine whether this is the case we must consult the activity series of metals. Activity Series of metals ranks metals in order of relative reactivity.

Type 2 Single Displacement reactions with Non metals. A + BC --> BA + C  Element A has replaced C (in the compound BC) to form a new compound BA and the free element C. Remember that A and C are both anions (negatively-charged ions) in this example. A forms an anion ( A is a non metal) Most frequently with Halogens (F, Cl, Br, I). As the elements become more electronegative they become more active.

Single Displacement Reactions are a type of redox reaction. In reactions, the element being displaced, is always reduced.

**Double Displacement Reaction**

A double displacement reaction is displacement of two elements in two different compounds. Compound + compound --> Compound + compound

In this cartoon our part of our two reactants are the big face and wide hat, and the skinny face and tall hat are switching there hats to form two new compounds, the big face with the tall hat and the skinny face with the wide hat.

AB + CD --> AD + CB  A and C are the cations (positively-charged ions), with B and D being the anions (negatively-charged ions). In a double displacement reaction the cations switch places and two new compounds are formed. When new compounds are formed there charges add up to zero.

A typical double replacement reaction can occur when two ionic compounds are mixed together. In water these ionic compounds split apart into their respective anions and cations. The cations now have an opportunity to swap anions. A reaction occurs if, by swapping anions, a product is formed that cannot split apart into anions and cations.

The reaction must be driven by one of three driving forces: Formation of a solid, formation of a gas or formation of a weakly-ionizing compound such as water.

**Combustion Reaction**

A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat.

Combustion reactions always involve molecular oxygen O2. Anytime anything burns, it is a combustion reaction. Combustion reactions are almost always exothermic (meaning they give off heat). For example when wood burns, it must do so in the presence of O2 and a lot of heat is produced.

Wood as well as many common items that combust are organic meaning they are made up of carbon, hydrogen and oxygen. When organic molecules combust the reaction products are carbon dioxide and water (as well as heat).

** Balancing Equations **

An important part to understanding reactions is having a correctly balanced equation. A balanced equation means that both the left and right sides are equal, or that there is the same number of reactants as products. This balance is based on the law of conservation of mass which states that in a chemical reaction all matter is conserved by rearranging atoms. For example, if you take the synthesis of water from hydrogen and oxygen gas.

** H **** 2 **** + O **** 2 **** --> H **** 2 **** O **

The reactants are hydrogen and oxygen which combine to make water, the product. To start there are 2 hydrogen and 2 oxygen on the reactant’s side, and 2 hydrogen on the product side, but only one oxygen. There is a missing oxygen atom, and since it cannot be destroyed, this reaction has not been balanced.

Due to the Law of Conservation of Mass which states that there is no loss of mass, there must be the same amount of each type of element before and after the reaction, either as a reactant or product. Since you cannot create or destroy matter, you must write an integer coefficient in front of (to the left of) each element, or compound, in the reaction to make sure every type of atom has the same number on each side of the reaction.

** __H__ **__** 2 **** + **__ **O** ** 2 **** --> __H__ **__** 2 **** O **__

__ To start balancing the equation, change the coefficient of water from a blank, which represents one, to a 2. __

** _H **** 2 **** + **
 * _O**** 2 **** --> 2H **** 2 **** O **

Still the reaction is not balanced. If all of the H’s are added up there are 2 on the reactant side, but 4 on the product side. In order to balance it, you must add hydrogen molecules to the reactant side of the reaction so that they are equal. This can be done by placing 2 in front of the hydrogen on the reactant side.

** 2H **** 2 **** + __O__ **__** 2 **** --> 2H **** 2 **** O **__

__ The reaction is now balanced, on the reactant side we have 4 Hydrogen and 2 Oxygen and on the product side we have 4 Hydrogen and 2 Oxygen. The reaction equation is: __

** 2 H2O --> 2 H2 + O2 **

__** Hints for balancing equations **__

__ The example is very simple, but the procedure stays the same for more complicated equations too. Some hints for balancing equations are listed below: __ __ · **Treat standard groups and polyatomic ions as an item** __ __ o Many equations have polyatomic ions like sulfates or phosphates, and if you can recognize a standard group, such as sulfate, phosphate, nitrate // etc //., then you should treat it as an individual item; treating groups as special items makes life a little easier. You can even replace the group with a neutral letter, like X to make it easier to see. Take the reaction where iron (III) oxide is put in sulfuric acid: __ Fe2O3 + H2SO4 Fe2(SO4)3 + H2O __ Let's make life easier by replacing **SO4** with **X**: __ Fe2O3 + H2X Fe2X3 + H2O __ Now we can balance the equation fairly easily: __ Fe2O3 + 3 H2X Fe2X3 + 3 H2O __ Replacing **X** with **SO4** gives the final equation: __ Fe2O3 + 3 H2SO4 Fe2(SO4)3 + 3 H2O __ *** This approach only works if the standard group remains unscathed throughout the reaction** __

__**o**__ __**You should leave the elements that appear //as// elements anywhere in the equation until last. This is because you can balance these elements without affecting any other elements.**__
__ Things to remember: __
 * 1) __**You may only put numbers in front of molecules, never altering the formula itself.**__
 * 2) __**Coefficients can be fractions, you can always double or treble all the numbers at a later stage.**__
 * 3) __**Balance complicated molecules with lots of different atoms first. Putting numbers in front of these may mess up other molecules, so use the simpler molecules to adjust these major changes.**__
 * 4) __**Use polyatomic ion groups such as sulfates, nitrates, phosphates, ammonium //etc.// that survive unscathed throughout the chemical reaction as single units to be balanced as a whole.**__
 * 5) __**Leave molecules representing elements until last. This means that any numbers you put in front of those molecules won't unbalance any other molecule.**__

**//__ Synthesis Reactions __//** Synthesis reactions take place when two or more elements or simple compounds form a single compound. There are five different types of synthesis reactions: **element + element**, **metal oxide + water**, **nonmetal oxide + water**, **metal oxide + nonmetal oxide**, and **metal chloride + oxygen**.

**__ Element + Element __** When two elements react, they will form a single compound. Common reactions between two elements are when hydrogen and oxygen form water (2H2 + O2 → 2H2O) or when sodium and chlorine react together to form sodium chloride (2Na + Cl2 → 2NaCl). These compounds are called **binary compounds**. In order to predict what the product of a reaction is, we need to know the **oxidation numbers** of the elements/compounds that are reacting together. To review, oxidation numbers help you keep track of the electrons in a reaction and what the charge of an element/compound is in the reaction. Consider the following reaction: ** 2Na + Cl2 → ???? ** The result of this reaction is 2NaCl. We know this because when we look at a periodic table, Na is in the IA column, which always has a charge of +1 (with H being an occasional exception). Cl is in the VIIA column which always has a -1 charge. The Cl has an extra electron, making it negatively charged, while the Na is missing an electron, making it positively charged. When the two react, the extra electron from the Cl goes to the Na and results in NaCl. As we learned earlier, reactions need to be balanced; we had two Na when we started and a Cl2 so have exactly enough to make 2NaCl.
 * Predicting the Product **

**__ Metal Oxide + Water __** When water and a metal oxide react, they will form what is called a **metallic hydroxide**. A metal oxide is a compound consisting of a metal and oxygen, such as calcium oxide (CaO) or barium oxide (BaO). In the below periodic table, the red area shows all of the metals that can form with oxygen (O2) to make a metallic hydroxide. Consider the following: ** CaO + H2O → ???? ** We know this is will result in a metallic hydroxide because we are combining water with a compound consisting of a metal and oxygen, a metal oxide. The product will always be composed of a metal, followed by any number of OH or hydroxide. Following this formula, the product turns out to be Ca(OH)2. We got this because we only have one of the metal elements, Ca, so we placed that first. Now all that’s left is an O and H2O; we need to make OH and we have two O and two H so we can make (OH)2. We put the hydroxide in parentheses to imply that the two is distributed to both the O and H.
 * Predicting the Product: **

**__ Nonmetal Oxide + Water __** When a nonmetal oxide and water react, they will form what is called a **nonbinary acid**. A nonmetal oxide is like a metal oxide only it is a nonmetal combined with oxygen, such as sulfur monoxide (SO) or carbon dioxide (CO2). The blue region of the previous periodic table shows the nonmetals. Consider the following reaction: ** Br2O + H2O → ???? ** We know that this will result in a nonbinary acid since we are reacting water with a compound consisting of a nonmetal and oxygen, a nonmetal oxide. The format of the product will begin with any number of H, followed by the nonmetal and oxygen. In this case, the product is 2HBrO because there is a common factor, 2, when we finish with H2Br2O2 so we simplify be “factoring” out a 2. When a metal oxide and a nonmetal oxide react, they will form what is called a **nonbinary salt**. The product of this reaction is a salt because in the previous reaction we had hydrogen where there is now a metal. Consider this reaction: ** Li2O + N2O5 → ???? ** Now for these products, you should know your polyatomic ions. The products are generally set up as the metals followed by a polyatomic ion. In this reaction, we first take the Li2 and place it in front, leaving us with O and N2O5. We can form the polyatomic ion NO3 out of these; in fact we can make two. In the end, we will have Li2(NO3)2 which can be reduced to 2 LiNO3 by the common factor of 2.
 * Predicting the Product **
 * __ Metal Oxide + Nonmetal Oxide __**
 * Predicting the Product **

When a metal chloride and oxygen react, they form what is called a **metal chlorate**. A metal chloride is a compound consisting of a metal and chlorine, such as sodium chloride (NaCl) or calcium chloride (CaCl2). Consider the following: ** 2NaCl + 3O2 → ???? ** Keep in mind the “chlorate” part of what we expect to be the product; remember that chlorate is ClO3. The final product should be a metal followed by chlorate. In this reaction, we have Na so we will place that in front, leaving us with 2Cl and 3O2. From this, we can make two ClO3. As we already have two Na, the product will come out to be 2 NaClO3.
 * __ Metal Chloride + Oxygen __**
 * Predicting the Product: **

**//__ Decomposition Reactions __//** Decomposition reactions are the reverse of synthesis reactions in a nutshell. They occur when a compound will divide into separate elements or simpler compounds. Recall from the previous section that **binary compounds** are composed of two elements, **metallic hydroxides** are composed of metal oxides and water, **nonbinary acids** are composed of nonmetal oxides and water, **nonbinary salts** are composed of metal oxides and nonmetal oxides, and **metal chlorates** are composed of metal chlorides and oxygen. Two reactions not discussed previously are **hydrogen peroxide** and **metallic carbonates**. Hydrogen peroxide is simply made up of water and oxygen (H2O2 → H2O and O2). Metallic carbonates are made up of metal oxides (the combination of a metal and oxygen) and carbon dioxide (CO2).

It is important to be able to recognize the formats of the various products formed by synthesis reactions so you know what the compound should break up into.

= Single Displacement = = = ...With Metals...  (One metal replaces another) **Generic Formula:** **AX + Y ---> YX + A** l__> Cation (+ ion) “Y” replaces__ __cation “A” to form new compound “YX”__

__//For Example...//__ __Fe + Cu(NO3)2 ---> Fe(NO3)2 + Cu Iron replaces Copper to form Iron IV Nitrate__ __Zn + 2HCl ---> ZnCl2 + H2 Zinc replaces Hydrogen to from Zn II Chloride__ __l__> (Don’t forget those diatomic elements!)

**Activity Series of Metals** As mentioned, the activity series lists metals ranked by their relative reactivity. We use this to see if the metal trying to replace the one in the compound is even strong enough. Take, for example, this reaction: Zn + 2HCl ---> ZnCl2 + H2 Zinc is way more reactive than hydrogen (see below), so it kicks out the hydrogen!

SHAPE \* MERGEFORMAT = Single Displacement = = = ...With Nonmetals...  (One nonmetal replaces another)

**Generic Formula:** **A + XY ---> XA + Y** l__> Anion (- ion) “A” replaces anion “Y”__ __to form new compound “XA”__ __//For Example://__ __Cl2 + 2NaBr ---> 2NaCl + Br2__ __Br2 + 2KI ---> 2KBr + I2__ __The most common situations of single displacement with nonmetals involve the halogens (F, Cl, Br, and I), because of their high reactivity.__

__...__ __Now that we know what we’re looking for, let’s give it a try!__

__Predict the products of these reactions:__ __ZnS + O2 ---> ??__ __Step 1- What will the free element replace? --> O2 replaces S__

__Step 2- Is the free element more reactive than the element in the compound? --> Yes.__

__Step 3- Do some criss-crossing to predict the new compound. -->__ __O-2 + Zn+2 --> ZnO__ __Step 4- Add in the free element (S8- Sulfur as a free element) and balance the final equation. -> 8ZnS + 4O2 ---> 8ZnO + S8__

__K + H2O ---> ??__ __Step 1- What will the free element replace? ---> K replaces H__

__Step 2- Is the free element more reactive than the element in the compound? (This is what that chart is for!)---> Yes.__

__Step 3- Do some more criss-crossing! (Careful Here! The H2O compound is a product of H+ and OH-)__ __K+2 + OH- ---> KOH__ __Step 4- Add in the free element (H2) and balance the final equation. --->__ __2K + 2H2O ---> 2KOH + H2__

= __Double Displacement__ =

= = __ The cations and anions of two different compounds __ __ switch places. __

__ **Generic Formula:** __ __ **AB + CD ---> AD + CB** __ __ ↕ ____↕ (“B” and “D” switch to form new compounds__ __“AD” and “CB”)__

__Keep in mind that, when it comes to writing actual formulas, you MUST write chemically correct formulas. DO NOT assume from the AD and CB examples that the product formulas will always be one-to-one in terms of positive and negative. The compounds will follow the same rules of ionic bonding we have been using all along, i.e. the total charge of the compound will equal 0.__

__A typical double replacement reaction can occur when two ionic compounds are mixed together. In water these ionic compounds split apart into their respective anions and cations. The cations now have an opportunity to swap anions.__

__A reaction occurs if, by swapping anions, a product is formed that cannot split apart into anions and cations.__

__//For example://__ __In the reaction of silver nitrate and potassium chloride, the silver, nitrate, potassium and chloride ions all begin in solution. When a silver ion combines with a chloride ion, it leaves the solution and becomes a solid. This drives the reaction to completion!!__ __……__ __AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)__ __l_____l__ __The reaction must be driven by one of three driving forces: Formation of a solid, formation of a gas or formation of a weakly-ionizing compound such as water. Let’s see what happens when the driving forces are not there.__ __……__ __NaNO3(aq) + KCl(aq) → NaCl(aq) + KNO3(aq)__ __Nothing happens!! Without a driving force there is no change in the solution so we say no reaction has taken place. Note that even though we can write an equation for the reaction, no reaction takes place without a driving force!!__

__**Precipitation in Double Displacement Reactions**__ __When a double displacement reaction occurs, the cations and anions switch partners, resulting in the formation of two new ionic compounds AD and CB, one of which is in the solid state. This solid product is an insoluble ionic compound called a precipitate. To decide whether a compound is soluble or not, we consult the Solubility Rules.__ __Take a look at this reaction:__ __Pb(NO3)2 (aq) + 2 NaCl (aq) → ??__ __l_____l The predicted products are lead(II) chloride (insoluble) and sodium nitrate (soluble). Since one of the predicted products is insoluble, a precipitation reaction is will occur. So....Pb(NO3)2 (aq) + 2 NaCl (aq) → 2 NaNO3 (aq) + PbCl2 (s)

This kind of reaction occurs when "AB" is an acid (possessing H+ ions) and "CD" is a base (possessing OH- ions). When these compounds switch their cations and anions, water (H2O) and a ionic compound are created. (Later on you will learn more about why this reaction is caused "neutralization" when you learn about pH and pOH in the Acids and Bases section.) Neutralization reactions are generally accompanied by a noticeable release of heat, making them...yes, exothermic. Take a look at this reaction: HSO(aq) + 2 LiOH (aq) ---> ?? The predicted products are water and lithium sulfate. Reaction Equation: HSO(aq) + 2LiOH (aq) → LiSO(aq) + 2 HO (l)
 * Neutralization Reactions**

In these reactions one of the products (AD or CB) after the double displacement is in the gaseous state, such as hydrogen sulfide (H2S) or ammonia (NH3). One of the products could also be carbonic acid (H2CO3) or sulfurous acid (H2SO3). Both carbonic acid and sulfurous acid are unstable and will decompose to form carbon dioxide and sulfur dioxide gases, respectively:
 * Gas Forming Reactions**

Carbonic acid................H2CO3 (aq) → H2O (l) + CO2 (g)

Sulfurous Acid...............H2SO3 (aq) → H2O (l) + SO2 (g)

Basically, this means that you have to watch out for these unstable compounds, because leaving them in your final balanced equation is WRONG. You MUST further break down these compounds, resulting in more products.

//For Example:// 2HNO3 (aq) + Na2SO3 (aq) → ?? The predicted products are sulfurous acid and sodium nitrate. However **sulfurous acid** So.... Reaction Equation: 2HNO3 (aq) + Na2SO3 (aq) → 2NaNO3 (aq) + **H2SO3 (aq) decomposes**
 * decomposes to sulfur dioxide and water**:

Final Equation: 2HNO3 (aq) + Na2SO3 (aq) → 2NaNO3 (aq) + **H2O (l) + SO2 (g)**

= Combustion Reactions = = = (boom)

These reactions occur when oxygen combines with another compound to create water and carbon dioxide. Anytime anything burns, it’s a combustion reaction, and obviously exothermic (produces heat). When it come down to predicting products of reactions, it doesn’t get any easier than this. Try one. I’m sure you’ll see what I mean.

//Example:// CH4 + O2 ---> ??

Because the compound on the reactants side contains carbon (C), you know that one of the products is going to be carbon dioxide (CO2). In addition, water will for created. So this gives you CH4 + O2 ---> CO2 + H2O

Now just balance the equation and you’re done!

CH4 + 2 O2 ---> CO2 + 2 H2O

Let’s try one that’s a little bit trickier....

C2H5NH2 + O2 ---> ??

Use the same idea as before. Every different element that is in the compound will show up in the products combined with O2. This will give us....

C2H5NH2 + O2 ---> CO2 + H2O + NO2

Now just balance the equation and...

4 C2H5NH2 + 15 O2 ---> 4 CO2 + 14 H2O + 4 NO2

...FIN.

Check this out for more practice!

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