Presentation on theme: "1 Chapter 7 Chemical Reactions. 2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end."— Presentation transcript:
1 Chapter 7 Chemical Reactions
2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end up with l The reactants turn into the products. Reactants Products
3 In a chemical reaction l The way atoms are joined is changed l Atoms arent created or destroyed. l Can be described several ways l In a sentence –Copper reacts with chlorine to form copper (II) chloride. l In a word equation Copper + chlorine copper (II) chloride
4 Symbols used in equations l the arrow separates the reactants from the products l Read reacts to form l Yields l The plus sign = and l (s) after the formula -solid l (g) after the formula -gas l (l) after the formula -liquid
5 Symbols used in equations l (aq) after the formula - dissolved in water, an aqueous solution. used after a product indicates a gas (same as (g)) (products only) used after a product indicates a solid (same as (s)) (products only)
6 Symbols used in equations l indicates a reversible reaction (More later) l shows that heat is supplied to the reaction l is used to indicate a catalyst used in this case, platinum.
7 What is a catalyst? l A substance that speeds up a reaction without being changed by the reaction. l A catalyst lowers the activation energy l Activation Energy- minimum amount of energy required by reacting particles in order to form the activated complex and lead to a reaction
8 Skeleton Equation l Uses formulas and symbols to describe a reaction l doesnt indicate how many. l All chemical equations are sentences that describe reactions.
9 Balancing Chemical Equations
10 Balanced Equation l Atoms cant be created or destroyed l All the atoms we start with we must end up with l A balanced equation has the same number of atoms of each element on both sides of the equation.
11 C + O 2 CO 2 l This equation is already balanced l What if it isnt already? C + O O C O O
12 C + O 2 CO l We need one more oxygen in the products. l Cant change the formula, because it describes what actually happens + O C O O C O CC
13 l Must have started with two C 2 C + O 2 2 CO + O CC O CC l Must be used to make another CO l But where did the other C come from? O O
14 Rules for balancing Write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) Check to make sure it is balanced.
15 Never l Change a subscript to balance an equation. –If you change the formula you are describing a different reaction. –H 2 O is a different compound than H 2 O 2 l Never put a coefficient in the middle of a formula –2 NaCl is okay, Na2Cl is not.
16 Example H 2 +H2OH2OO2O2 Make a table to keep track of where you are at RP H O Need twice as much O in the product H 2 +H2OH2OO2O2 2 2 Changes the OAlso changes the H 4 Need twice as much H in the reactant 2 Recount 4 The equation is balanced, has the same number of each kind of atom on both sides
17 Example H 2 +H2OH2OO2O2 RP H O This is the answer Not this
18 Examples CH 4 + O 2 CO 2 + H 2 O
19 Examples AgNO 3 + Cu Cu(NO 3 ) 2 + Ag
20 Examples Al + N 2 Al 2 N 3
21 Examples P + O 2 P 4 O 10
22 Examples Na + H 2 O H 2 + NaOH
23 Techniques l If an atom appears more than once on a side, balance it last. l If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there. l C 4 H 10 + O 2 CO 2 + H 2 O
24 Types of Reactions Predicting the Products
25 Types of Reactions l There are too many reactions to remember l Fall into categories. l We will learn 5 types. l Will be able to predict the products. l For some we will be able to predict whether they will happen at all. l Must recognize them by the reactants
26 #1 Combination Reactions l Combine - put together l 2 elements, or compounds combine to make 1 compound. Ca +O 2 CaO SO 3 + H 2 O H 2 SO 4 l We can predict the products if they are two elements. Mg + N 2
27 Write and balance Ca + Cl 2
28 Write and balance Fe + O 2 iron (II) oxide
29 Write and balance Al + O 2 l Remember that the first step is to write the formula l Then balance l Also called synthesis reaction
30 Combining two compounds l If they tell you it is combination, you will make one product l Two compounds will make a polyatomic ion. l CO 2 + H 2 O l H 2 O + Cl 2 O 7
31 #2 Decomposition Reactions l decompose = fall apart l one reactant falls apart into two or more elements or compounds. l NaCl Na + Cl 2 l CaCO 3 CaO + CO 2
32 #2 Decomposition Reactions l Can predict the products if it is a binary compound l Made up of only two elements l Falls apart into its elements lH2OlH2O
33 #2 Decomposition Reactions l HgO
34 #2 Decomposition Reactions l If the compound has more than two elements you must be given one of the products l The other product will be from the missing pieces l NiCO 3 NiO + H 2 CO 3 (aq) CO 2 +
35 #3 Single Replacement l One element replaces another l Reactants must be an element and a compound. l Products will be a different element and a different compound. Na + KCl K + NaCl F 2 + LiCl LiF + Cl 2
36 Na + KCl K + NaCl Na K Cl
37 F LiCl 2 LiF + Cl 2 F Li Cl F Li Cl Li
38 #3 Single Replacement l Metals replace metals (and hydrogen) Al + CuSO 4 Zn + H 2 SO 4 l Think of water as HOH l Metals replace one of the H, combine with hydroxide. Na + HOH
39 #3 Single Replacement l We can tell whether a reaction will happen l Some are more active than other l More active replaces less active l There is a list on page 333
40 #3 Single Replacement l There is a list on page 333 l Higher on the list replaces lower. l If the element by itself is higher, it happens, l if element by itself is lower, it doesnt
41 #3 Single Replacement l Note the * l H can be replaced in acids by everything higher l Only the first 4 (Li - Na) react with water.
42 #3 Single Replacement Al + HCl
43 #3 Single Replacement Fe + CuSO 4
44 #3 Single Replacement Pb + KCl
45 #3 Single Replacement Al + H 2 O
46 #3 Single Replacement l What does it mean that Ag is on the bottom of the list?
47 #3 Single Replacement l Nonmetals can replace other nonmetals l Limited to F 2, Cl 2, Br 2, I 2 l The order of activity is that on the table. l Higher replaces lower. F 2 + HCl Br 2 + KCl
48 #4 Double Replacement l Two things replace each other. l Reactants must be two ionic compounds or acids. l Usually in aqueous solution NaOH + FeCl 3 l The positive ions change place. NaOH + FeCl 3 Fe 3+ OH - + Na + Cl - NaOH + FeCl 3 Fe(OH) 3 + NaCl
50 #4 Double Replacement l Will only happen if one of the products –doesnt dissolve in water and forms a solid –or is a gas that bubbles out. –or is a covalent compound usually water. l Polyatomic ions dont change from side to side
51 Complete and balance l assume all of the reactions take place. CaCl 2 + NaOH CuCl 2 + K 2 S KOH + Fe(NO 3 ) 3
52 Complete and balance KOH + Fe(NO 3 ) 3 H 3 PO 4 + Ca(OH) 2
53 How to recognize which type l Look at the reactants l E for element l C for compound l E + E Combination l CDecomposition l E + CSingle replacement l C + CDouble replacement
54 Last Type l Combustion l A compound composed of only C H and maybe O is reacted with oxygen l If the combustion is complete, the products will be CO 2 and H 2 O. l If the combustion is incomplete, the products will be CO and H 2 O. l or just C and H 2 O. l O 2 will always be the second reactant
55 Examples l Complete combustion of C 4 H 10 l Incomplete combustion of C 4 H 10
56 Examples l Complete combustion of C 6 H 12 O 6 l Incomplete combustion of C 2 H 6 O
57 Ionic Compounds and acids l Fall apart into ions when they dissolve l Thats why they conduct electricity when dissolved. l So when we write them as (aq) they are really separated l NaCl(aq) is really Na + (aq) and Cl - (aq) l K 2 SO 4 (aq) is really K + (aq) and SO 4 2- (aq)
58 Reactions in aqueous solutions l Many reactions happen in solution l Makes it so the ions separate so they can interact. l Solids, liquids, and gases are not separated, only aqueous
59 Chapter 7 Summary
60 An equation l Describes a reaction l Must be balanced to follow the Law of Conservation of Mass l Can only be balanced by changing the coefficients. l Has special symbols to indicate state, and if catalyst or energy is required.
61 Reactions l Come in 5 types. l Can tell what type they are by the reactants. l Single Replacement happens based on the activity series l Double Replacement happens if the product is a solid, water, or a gas.
62 The Process 1. Determine the type by looking at the reactants. 2. Put the pieces next to each other based on type 3. Use charges to write the formulas –Elements get 2? 4. Use coefficients to balance the equation.