Chapter 6 Lecture Notes: Reactions - Saddleback College

1 Chemistry 108 Lecture notes Chapter 6: Reactions 1 Chapter 6 Lecture notes : Reactions Chapter 6 Educational Goals 1. Define the term "chemical reaction". 2. Given the reactants and products in a chemical reaction, the student will be able to write and balance chemical equations. 2. Identify oxidation, reduction, combustion, hydrogenation Reactions . 3. Identify hydrolysis, hydration, and dehydration Reactions of organic compounds. 4. Use stoichiometric calculations to determine the theoretical yield, and percent yield of a reaction. 5. Describe the difference in energy changes ( G) for spontaneous and nonspontaneous Reactions , and list the factors that affect the rate of a chemical reaction.

2 Reactions involve changes in matter resulting in new_____. In chemical Reactions , the covalent and ionic bonds that hold elements and compounds together are _____ and/ or _____ bonds are formed. Evidence of Chemical Reactions 1) The _____ changes 2) A _____ is formed. 3) A _____ is formed. 4) _____ is given off or the appearance of_____. Chemistry 108 Lecture notes Chapter 6: Reactions 2 5) _____is emitted. 6) A new _____ is emitted. 7) The _____ changes. 8) A permanent, new _____ is formed. Reactions and Energy Changes Energy can be _____ in a chemical reaction. Energy can be_____ in a chemical reaction. Chemical Equations Chemical changes are represented using_____.

3 (g) = _____ (l) = _____ (s) = _____ (aq) = _____ (dissolve in water) Chemistry 108 Lecture notes Chapter 6: Reactions 3 Things to remember when writing equations: Burning in air means reacting with _____. Identify the _____of each chemical Metals are solids, except for Hg which is liquid Identify elements that come as _____ molecules -The following elements come as diatomic elements: _____ _____ _____ _____ _____ _____ _____ Balancing Chemical Equations In a balanced chemical equation, the same _____ of each atom appears on each side. Matter is neither created or destroyed in a chemical reaction Method for Balancing 1) Make a table and count all atoms on each side of the equation If H2 or O2 is present, list them last.

4 A polyatomic ion may be counted as one element if it does not change in the reaction. 2) Balance an element in the table by adding coefficients to the equation (start with the first element on the list) 3) Recount each atom and Repeat step 2 for all atoms until balanced. Example: _____H2(g) + _____O2(g) _____ H2O(g) Chemistry 108 Lecture notes Chapter 6: Reactions 4 Example: _____N2 + _____O2 _____N2O Reactants Atom Products N O Example: _____N2 + _____O2 _____NO Reactants Atom Products N O Example: _____Mg(s) + _____O2(g) _____MgO(s) Reactants Atom Products Mg O Example.

5 A polyatomic ion may be counted as one element if it does not change in the reaction _____Al + ____FeSO4 _____Al2(SO4)3 + _____Fe (SO4) Al Fe Chemistry 108 Lecture notes Chapter 6: Reactions 5 Balance the following reaction for the combustion of propane: _C3H8(g) + ___O2(g) ___CO2(g) + __H2O(g) Avoiding Common Errors When Balancing Chemical Equations Chemistry 108 Lecture notes Chapter 6: Reactions 6 stoichiometry (Pronounced: STOY-KEE-AHM-EH-TREE) stoichiometry deals with calculations about the _____ of reactants and products involved in a chemical reaction.

6 stoichiometry allows a chemist or scientist to know how much of an element or reactant to use and how much product is expected to come out of the reaction. A _____ _____allows us to predict which reactant (if any) will run out first and how much product can be expected to form. Before we do calculations with chemicals, let s do something we are all familiar with: Food!!! Suppose you want to make as many cheese sandwiches as possible for lunch. If you have 20 slices of bread, how many slices of cheese do you need? 2 bread slices + 1 cheese slice 1 sandwich Let s do the same calculation for a chemical reaction now! Carbon monoxide reacts with oxygen to produce carbon dioxide: 2CO + O2 2CO2 How many CO2 molecules are produced from 2 CO molecules?

7 _____ How many O2 molecules are needed to produce 2 CO2 molecules? _____ How many CO molecules are needed to react with 1 O2 molecule?_____ How many moles of CO2 are produced from 2 moles of CO? _____ How many moles of O2 are needed to produce 2 moles of CO2? _____ How many moles of CO are needed to react with 1 mole of O2? _____ = Chemistry 108 Lecture notes Chapter 6: Reactions 7 Beginning with moles of CO, how many moles of CO2 will be made if all of the CO is used up? 2CO + O2 2CO2 How many moles of O2 will be needed to react with moles of CO? How many moles of CO are needed to produce moles of CO2? Assume that you have an unlimited supply of O2.

8 Since we can not measure the number of moles on a balance in the lab, we are usually given the number of grams of a reactant or product and need to determine the number of grams of other reactants or products in a reaction. These calculations only work with_____, not with mass (grams)! We will see why that is using our cheese sandwich example. If you have 20 grams of bread, how many grams of cheese do you need?..need more information!!!! Since the coefficients in an equation give us the ratio of _____, we must convert grams to moles in our calculations. = = = Chemistry 108 Lecture notes Chapter 6: Reactions 8 The re-breather units used by some firefighters convert exhaled carbon dioxide (CO2) into oxygen gas (O2).

9 How many grams of oxygen (O2) can be produced from grams of potassium superoxide (KO2)? 4KO2 (s) + 2CO2(g) 2K2CO3(s) + 3O2(g) How many grams of oxygen (O2) can be produced from grams of potassium superoxide (KO2)? How many grams of (CO2) will react with grams of potassium superoxide (KO2)? 4KO2 (s) + 2CO2(g) 2K2CO3(s) + 3O2(g) = = Chemistry 108 Lecture notes Chapter 6: Reactions 9 How many grams of (KO2) are needed to produce g of O2 4KO2 (s) + 2CO2(g) 2K2CO3(s) + 3O2(g) You try one: How many grams of silver will completely react with g of sulfur? 2 Ag(s) + S(s) Ag2S(s) In this course, we will always be given the amount of one reactant and we will assume an excess supply of all other reactants.

10 If you are curious as to how to do stoichiometric calculations with a limited amount of all reactants, read the section in the text about limiting reagents. (email me for worksheets) = Chemistry 108 Lecture notes Chapter 6: Reactions 10 Percent Yield The amount of product obtained from a reaction is called the actual yield. To indicate how well the actual yield agrees with the theoretical (calculated) yield, chemists report the_____ _____: x 100% Example: A drug company runs a large scale reaction to prepare the pain reliever acetaminophen.