chapter8_akdb



=**Chemical Reactions and Equations **=

Introduction
Chemical reactions are necessary for our daily lives, from the burning of gas to run our cars to lighting a match. Equations are used to explain these reactions in a scientific form and to understand it on a molecular level. On technical terms, a chemical reaction is the process by which one or more substances are changed into one or more different substances. (Textbook) The initial chemicals are reactants and the chemicals after the reaction are the products. A chemical equation represents, with symbols and formulas, the reaction taking place and the amounts in both the product and reactant.

 **Chapter 8, Section 1 **

**Chemical Reaction?**
Even though one cannot know for certain whether a reaction has taking place without analysis, there are four indications a person can look for to see if a chemical reaction is probably taking place. 1. Evolution of energy as heat or light, if there is fire or any kind of bright light emitting, most likely a reaction took place. 2. Production of a gas, if there are bubbles, a visible gas, or a smell of some sort, most likely a reaction took place. 3. Formation of a precipitate, which is a solid that is produced as a result of a chemical reaction in a solution and that separates from the solution (Textbook) 4. Change in color



**Rules **
There are also three rules that must be followed when writing, and reading, a chemical equation. 1. The equation must represent known facts, in other words every part of the formula must have been proved in an earlier theory in someway. 2. The equation must contain the correct formulas for the reactants and products, for this step one must have previous knowledge of chemical formulas and elements. An example of this would be that one should know that nitrogen, oxygen, fluorine, chlorine, bromine, iodine, hydrogen, are all diatomic, which means they almost always exist in pairs. An easy way to remember this is **__Br__ __I__ __N__ __Cl__ __H__ __O__ __F__** (brink-el-hof) which is all of the diatomic. The letters in the name represent the elements that always exist in pairs. 3. The law of conservation of mass basically states that atoms can’t be destroyed or created as a reaction of the equation. Instead, a person can use a coefficient, a small or whole number that appears in front of a formula in a chemical equation (Textbook), to help them form formulas.

Helpful Hints
When you are doing the first step it helps to write out the word equation, where all the chemicals and compounds are written in word form. An example of this is sodium oxide + water à sodium hydroxide. Next you want to write out the formula using the symbols and formulas representing the parts of the formula. This is where it can get a little tricky the first few tries. In our example it would be Na2O + H2Oà NaOH. For this next part of the step ignore the subscripts. You get the result on the right side by balancing using the charges of the elements, Na is +1, Oxygen is -2, and hydroxide is 1-, so by having NaOH, Na is +1, OH is -1 so it is electronically balanced. The only problem with this is that the two sides of the equation are not chemically balanced. They aren’t balanced because there is 2 hydrogen, 2 oxygen, and 2 sodium on the left while only 1 of each on the right When you are balancing you are NOT allowed to alter the subscripts. Instead you use coefficients. Coefficients can __only__ be added at the beginning of a compound or element! So, if we add 2 in front of the product (NaOH) it multiplies all of the chemicals in the product so now there are 2 hydrogen, 2 oxygen, and 2 sodium on the right, balancing the equation.

Other Symbols
-An arrow pointing to the right means to yield, which is used in normal chemical reactions. -One arrow pointing to the right and one under that pointing to the left is used to indicate a reversible reaction, which is a chemical reaction in which the products re-form the original reactants (textbook). -(s) means that the certain reactant or product is in a solid state. -(l) means the reactant or product is in a liquid state. -(g) means the reactant or product is in a gas state. -(aq) means the reactant or product is dissolved in water [aqueous]. -An up arrow indicates a gaseous product. -A down arrow indicates a precipitate. -A right arrow with the symbol delta, or heat, means the reactants are heated -A right arrow with x (variable) atm above it indicates the pressure at which the reaction is carried out -A right arrow with the word pressure above it indicates the reaction is carried out exceeds pressure normally in our atmosphere. -A right arrow with the x (variable) degrees C indicates the temperature the reaction should be carried out at -A right arrow with a catalyst above it indicates the reaction uses this catalyst to alter the rate of the reaction.



<span style="color: #0fa3e6; font-family: Tahoma, Geneva, sans-serif;">More Hints
1. Al + Br2 --> AlBr3 (this first step is pretty simple, Al has a charge of +3, while Br has a charge of -1 so all you have to do is add a third Br to balance the product.) 2. 2Al+ 3Br2 --> 2AlBr3 (in this step __remember__ you can only use coefficients! Since you added a Br in the first step to balance, you’ll need to balance the two sides. If you add 2 in front of the product you’ll have 2 Al’s and 6 Br’s. So, you add 2 in front of the reactant Al you’ll balance the Al’s and you if you add 3 in front of the reactant Br you’ll have 6, so the Br’s will be balanced)

1. Ca+O2 --> CaO (once again, this first step is very easy, Ca has a charge of -2 and O has a charge of +1 but since there are 2 of them the total charge is +2 which balances the product) 2. 2Ca+O2 --> 2CaO (Since there is only 1 oxygen in the product, you’ll have to use coefficients to balance the product and the reactants. Since you want 2 oxygen in the product, you’ll put a 2 in front of the product, balancing the oxygen in both parts. But, now the calcium is unbalanced because there are 2 in the product and 1 reactant. So, you’ll put a 2 in front of the reactant calcium, making 2 calcium in the reactants and 2 in the products, balancing the equation.

<span style="color: #00070a; font-family: Tahoma, Geneva, sans-serif;"> ** Chapter 8, Section 2: Types of chemical reactions **

<span style="color: #0fa3e6; font-family: Tahoma, Geneva, sans-serif;">
<span style="font-family: Tahoma, Geneva, sans-serif;">**Synthesis Reactions** (A + X --> AX) **-** at least two substances A and X are either elements or compounds but AX has to be a compound because of the two elements. Reactions of elements with oxygen and sulfur. When an element is combined with oxygen it produces an oxide. Most metals are able to form oxides. Most elements will act similarly with sulfur and will produce sulfides. Non metals can also form oxides but when they react the product is a dioxide. Reactions with metals and halogens. the halogens can react with most metals to from either ionic or covalent compounds. Group one and two on the Periodic Table will react to form ionic compounds. Reactions with oxides. Oxides that are made with an active metal will react with water from a metal hydroxide.


 * Decomposition reaction** (AX --> A + X) **-** One compound is broken apart by a reaction to form at least two simpler substances. As in the synthesis AX must be a compound but A and X can be either element or compounds. Most decomposition reactions will only occur if energy is added. The most common ways of adding energy are by heat and electricity. When you use electricity to break down a substance it is called electrolysis. Of all the decomposition reactions the most simple one is the decomposition of a binary compound into the elements that it is made of. Oxides that are less active must be heated to decompose. When you heat a metal carbonate it will always break down into a metal oxide and carbon dioxide gas. But when Metal Hydroxide is heated the result is always at least one metal oxide and water. Metal chlorate decomposes and creates a Metal Chloride and oxygen. Some acids will decompose to form a nonmetal oxide and water.

Displacement of hydrogen in water by a metal. Metals that have an extremely high activity will react with water to form a metal hydroxide and hydrogen. Less active metals will react to steam and will create a metal oxide and a hydrogen gas. Displacement of hydrogen in an acid is by a metal. Some acids will react with an active metal to produce an metal compound and hydrogen. Displacement of Halogens is where one halogen can replace a different halogen in a compound. The halogens can each replace any halogen below it, but not above it. This is because the halogen group is most reactive at the //top// of the periodic table.
 * Single displacement** (A + BX --> AX + B) reactions happen when one element replaces a similar element in a compound. Not a lot of energy is required in a single displacement reaction. It is displacement of a metal in a compound by a different metal. In this reaction the more active metal is placed in the less active aqueous solution the solid metal will change its place with the metal in the solution.


 * Double displacement** (AX+BY --> AY+ BX) reactions are where ions of both compounds change places when they are in an aqueous solution. One of the compounds will be a gas and be released from the solution and the other will be dissolved in the solution. The precipitate is formed when the cation of one compound and the anion of the other react and form a insoluble compound. Sometimes a stable compound like water can be formed.

<span style="font-family: Tahoma, Geneva, sans-serif;">**Combustion Reactions -** when a substance and **oxygen** combine and create enough energy that it produces light and heat. Ex: The burning of fossil fuels is a combustion reaction.

** Now for some example problems: ** ~On a separate piece of paper write down these problems, then balance and tell what type of reaction it is. The answers are at the bottom.

­ **Na + Cl2 --> NaCl**

­ //Fe + O2 --> Fe2O3//

­ **Na2O + H2O --> NaOH**

­ //SO3 + H2O --> H2SO4//

­ **HCl + Mg(OH)2 --> MgCl2 + H2O**

//­ Zn + CuSO4 --> Cu + ZnSO4//

** Chapter 8, Section 3: Activity Series of the Elements **

<span style="font-family: Tahoma, Geneva, sans-serif;">**Activity** is the elements capability to react to other substances.

<span style="color: #0fa3e6; font-family: Tahoma, Geneva, sans-serif;">Activity Series
<span style="font-family: Tahoma, Geneva, sans-serif;">An activity series is a list of elements which are arranged in the order of the elements willingness to form a certain reaction. They are used to tell whether a reaction can take place or not. The order of the activates series is typically based on their single-displacement reactions. The element with the most activity goes at the //top// of the list. It is able to replace every element with a lower activity in a single-displacement reaction. Once the elements get farther down, they can only replace the less active elements but not the ones above it.

<span style="color: #0fa3e6; font-family: Tahoma, Geneva, sans-serif;">Hints
<span style="color: #0fa3e6; font-family: Tahoma, Geneva, sans-serif;"> With **metals** a greater activity will mean that it will be easier to **lose** an electron so it can be a positive ion. With **nonmetals** a greater activity means that they can more easily **gain** electrons to make them negative ions.


 * REMEMBER:** activity series are supposed to __help__ you find the outcomes but are only based on experiment.

<span style="display: block; font-family: Tahoma, Geneva, sans-serif; text-align: center;">Answers:


 * 2Na + Cl2 --> 2NaCl (synthesis Replacement)**

­ 2//Fe + 3O2 --> Fe2O3 (synthesis replacement)//

­ **Na2O + H2O --> 2NaOH (synthesis replacement)**

­ //SO3 + H2O --> H2SO4 (synthesis replacement)//

­ 2**HCl + Mg(OH)2 --> MgCl2 + 2H2O (double replacement)**

//­ Zn + CuSO4 --> Cu + ZnSO4// //(double replacement)//