chapter8_nocfav

=CHAPTER 8: Chemical Equations and Reactions =

//Describing Chemical Reactions //

Chemical Reactions are processes by which one or more substances are changed into one or more different substances.

· The original substances are known as the reactants · The resulting substances are known as the products (what the reactant is converted to)


 * The Law of Conservation of Matter** relates to chemical reactions and equations because this law states that in ordinary chemical reactions matter is neither created nor destroyed.

· mass can't be created or destroyed in any ordinary chemical reaction. Chemical Equation · represents with symbols and formula, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction Example:
 * Law of Conservation of Mass**

(NH4)2Cr2O7(s) N2(g)+Cr2O3(s)+4H2O(g)

Indications of a Chemical Reaction To know for certain that a chemical reaction has taken place requires evidence that one or more substances have undergone a change in identity. After analysis of the products you can have absolute proof of a change. There are easily observed changes that indicate that a chemical change has occurred.

1. Evolution of energy as heat and light: · If the matter releases energy both of heat and light then that is pretty strong evidence that a chemical change has occurred. But if they heat or light by themselves it occurs that is not necessarily a sign of a chemical change.

2. Production of a Gas · The evolution of gas bubbles when two substances are mixed is often evidence of a chemical reaction. An example of this is when you mix baking soda and vinegar. 3. Formation of a Precipitate · A precipitate is a solid that is produced as a result of a chemical reaction in a solution and that separates from the solution. If this occurs when two substances are mixed then a reaction has most likely occurred. -A formation of a Precipitate is often from the mixing of two soluble compounds. -These reactions usually occur in //**aqueous**// solutions

4. Color Change · A color change often indicates a chemical reaction ex: when you mix together the iodinate ion (IO3) and the bisulfate ion (HSO3) they will combine and after mixing turn black.

(To see a color change in a chemical reaction with Potassium Permanganate go to this link: http://www.youtube.com/watch?v=QRSBchx81pg )


 * A balanced Chemical Equation is a description of the reaction that is taking place. Every atom that appears on the left side(reactant) MUST appear o the right side(products). For instance, if 5 Carbons are on the left side of the equation, 5 Carbons MUST be on the right side. This is established by adding coefficients. (information from [])
 * A balanced Chemical Equation shows information such as which chemical species are the reactants and which species are the products. It may also indicate in which state of m atter the reactants and products exist. Special conditions of heat, temperature, and catalysts may also be in the balanced chemical equation.
 * The coefficients(the number in front of the products and reactants) indicate the number of each reactant that is used and the number of each product is formed. (The coefficients will balance your equation based on the Law of Conservation of Matter)

Characteristics of Chemical Equations A properly written chemical equation can summarize any chemical change. 1. The equation must represent known facts. 2. The equation must contain the correct formulas for the reactants and products. 3. The law of conservation of mass must be satisfied. 4.To balance numbers of atomes, add coeficients are necessary. A //**coefficient**// is a small whole number that appears in front of a formula in a chemical equation.

Word and Formula Equations Word Equations is an equation in which the reactants and products in a chemical reaction are represented by words. Ex: methane + oxygen carbon dioxide + water
 * The arrow is read as react to yield or just yield.

Formula Equations represent the reactants and products of a chemical reaction are their symbols or formulas. Ex: CH4(g) + O2(g) CO2(g) + H2O(g) (not balanced)
 * The g is parentheses after each formula indicates that the corresponding substance is in the gaseous state.

To make the equation complete one must balance the equation which is carried out by inserting coefficients. A coefficient multiplies the number of atoms of each element indicated in a chemical formula.

**Step-by-Step of Balancing an Equation** The equation is: Hydrogen gas and Oxygen gas combine to form water -The unbalanced equation is **H2 + O2 => H2O** -We look at the numbers of Hydrogens and Oxygens on each side and see that there are __2 Hydrogens on left side and 2 Hydrogens on the right side. The Hydrogens are balanced, for now.__ -We now look at the Oxygens. There are __2 on the left and 1 on the right, the Oxygens need to be balanced.__ -To balance the Oxygens, we place a coefficient of 2 on the right side of the equation in front of the water, which gives us: -We now see that the Hydrogens are unbalanced, and to balance them we place a 2 in front of the Hydrogen on the left side of our equation. -After this, our equation is: **2H2 + O2 => 2H2O** -There are now 4 Hydrogens on the left, 4 Hydrogens on the right, 2 Oxygens on the left, and 2 Oxygens on the right. -Our chemical equation is now balanced :)
 * H2 +O2 => 2H2O**

Significance of a Chemical Equation 1. The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products. 2. The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients. 3. The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction.

Balancing Chemical Equations 1. Identify the names of the reactants and the products, and write a word equation. 2. Write a formula equation by substituting correct formulas for the names of the reactants and the products. 3. Balance the formula equation according to the law of conservation of mass. · The different types of atoms should balance at one time. · Balance the atoms of elements that are combined and that only appear once on each side of the equation first. · Next balance the polyatomic ions that are single units on each side of the equation. · Finally balance H atoms and O atoms after atoms of all of the other elements have been balanced. 4. Count atoms to be sure that the equation is balanced. Br, I, N, Cl, H, O, F example: Oxygen- O**2** EXAMPLE: 2H2 (g) + O2(g) => 2H2O(g)
 * There are seven elements that are diatomics that are not by themselves.

-> and example of a chemical reaction. The equation for this is ** H2 + Cl2 => 2HCl ** (picture from [])

//Types of Chemical Reactions //

There are multiple types of chemical reactions under that heading, explained so clearly in Section 1. These are basic outlines only. The definitions themselves are, like all Chemistry, suspect to change upon future discoveries.

Single letter (A) refers to an element. Double letter (AX) denotes a compound.

1. A **//synthesis reaction //** is where two or more substances combine to form a new compound. a. Also known as compound reactions, the component “substances” can be elements or compounds. b. These equations are demonstrated as __A + X → AX__ c. The picture below demonstrates synthesis reaction. d. Non-metals undergo synthesis reactions with oxygen to form oxides. e. most metals react with halogens to form ionic or covalent compounds. ex. 2Na (s) + Cl2 (g) => 2NaCl (s)

ex: 2H2 + O2 => 2H2O

This is a picture of a synthesis reaction : https://reich-chemistry.wikispaces.com/file/view/IMG.jpg

2. A //**decomposition reaction** // takes place when one compound undergoes a change back to two of its parts. a. These are the opposite of synthesis reactions. b. Such a reaction is w ritten as __AX → A + X__ c. The picture below demonstrates decomposition reaction. d. simplest kind of decomposition reaction is the decomposition of a binary compund into its elements. ex:2KClO3 => 2Kl +3O2

3. A reaction seen most commonly in aqueous solutions, a **//single-displacement reaction //**<span style="color: rgb(0,128,128); font-family: Georgia, serif;"> causes one element to replace another in a compound. a. These reactions use less energy than the previous two. b. The equation can be written as __A + BX → AX + B__ or __Y + BX → BY + X__

ex: Cu + AgNO3 => Ag + CuNO3

This is a picture of what the reaction would look like in real life at a high school dance:

http://www.usoe.k12.ut.us/CURR/Science/sciber00/8th/matter/images/1REPLACE.GIF

4. <span style="color: rgb(128,0,128); font-family: Georgia, serif;">The next step would of course be **//<span style="color: rgb(128,0,128); font-family: Georgia, serif;">double-displacement reactions //**<span style="color: rgb(128,0,128); font-family: Georgia, serif;">. Despite the name, these are much more complex than the single-displacement variety. a. One involved compound is typically a //precipitate//, an insoluble gas that bubbles out of the solution, or a molecular compound like water. b. The other compound dissolves in the solution and is usually soluble. c. These are written in equation form as __AX + BY → AY + BX__ d. Formation of a percipitate occurs when the cations of one reaction combines with the anion of another reactant to form an insuoluble or slightly soluble compound. ex: Cu(NO3)2 + 2NaOH => Cu(OH)2(s) + 2NaNO3(aq)

This is a picture of a double-displacement reaction:

http://farm4.static.flickr.com/3481/3209937064_ac25afbc31.jpg

5. <span style="color: rgb(0,213,255); font-family: Georgia, serif;">The final type of reaction is the **//<span style="color: rgb(0,213,255); font-family: Georgia, serif;">combustion reaction //**<span style="color: rgb(0,213,255); font-family: Georgia, serif;">. The most visually thrilling form, these are caused by a substance to combine with oxygen and release energy as light and heat. Or you could just say it explodes. a. This reaction produces water vapor. b. Commonplace examples of this type are anything you would burn for light or heat, such as wood, gas, coal, or propane. c. These equations are written as __A + O2 → BOOM__ d. to be combined with oxygen (O2) e. There are two types of combustion reactions: 1) non-hydrocarbon ex. 2Ca+O2 => 2CaO 2)Hydrocarbon (C+H) ex. CH4+2O2 => 2H2O+CO2 f. Burning of natural gas, propane, gasoline, and wood are examples of a combustion reaction. ex:CH4 + 2O2 => 2H2O + CO2
 * water is always a product in a combustion reaction

//<span style="font-size: 140%; color: rgb(255,0,255); font-family: Georgia, serif;">Activity Series of the Elements //

List of elements organized according to how easy the elements undergo certain chemical reactions.

· Nonmetals gain electrons easier with more activity, while metals lose electrons easie

· More active elements on the activity series can replace elements below it in a single-displacement reaction

· According to the activity series, aluminum replaces zinc, so: - 2Al + 3ZnCl2 à 3Zn + 2AlCl3

· Cobalt can’t replace sodium, though, so: - Co + 2NaCl à no reaction

· Activity series are used to predict whether something will react, but just because an equation can be written doesn’t mean a reaction will occur.

<span style="font-size: 140%; color: rgb(255,0,255);">//Practice Problems://

Balance this equation. H2O2 (aq) => H2O (l) + O2 (g)

What are the 7 diatomics?

Write the word equation: Zn(s) + HCl(aq) => ZnCl2(aq) + H2(g) *<span style="background-color: rgb(255,255,0);">not balanced

Complete this mole equation: Lithium and nitrogen ( N2) react to form Lithium Nitrate (Li3N) Write equation and balance it to solve.

How many moles of H3PO3 are required to form 15 moles of H3PO4? How many moles of PH3 do you get as well? Balance the equation to get the answer. H3PO3 => H3PO4 + PH3

Solve this equation and say what type of reaction it is: Fe(NO3)3 +3NaOH => Fe(OH)3 (s) + 3NaNO3 (aq)

Solve this equation and say what type of reaction it is: Ammonium carbonate ( (NH4)2CO3 )and calcium chlorate (CaCl2) react