1 Chapter 6 Chemical Reactions

2 Indications of a Chemical Reaction? l Color change l Odor change l Precipitate formed l Energy change (temperature/light) l Gas released

3 Chemical Reactions l Reactants - the substances you start with l Products- the substances you end up with l The reactants turn into the products.

4 In a Chemical Reaction… l The way atoms are joined is changed l Atoms aren’t created or destroyed. In a sentence: l Copper reacts with chlorine to form copper (II) chloride. In a word equation: l Copper + chlorine  copper (II) chloride

5 Symbols Used in Equations l Arrow  –“reacts to form” l Plus sign + –“and” l (s), (g), (l)after the formula l (aq) after the formula

6 Diatomic elements l H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2, and At 2 (The –gens and the –ines)

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8 Practice l Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.

9 Practice l Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

10 Practice - The Other Way Fe(g) + O 2 (g)  Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq)  Ag(s) + Cu(NO 3 ) 2 (aq)

11 Balancing Chemical Equations

12 Conservation of Matter l Atoms cannot be created or destroyed l A balanced equation has the same number of each element on both sides of the equation.

13 C + O 2  CO 2 C + O O  C O O

14 C + O 2  CO Cannot change the formula C + O  C O O

15 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.

16 Never NEVER change a subscript to balance an equation! NEVER add a coefficient to the middle of a formula!

17 Example H 2 + O 2  H 2 O Make a table

18 Examples 1. CH 4 + O 2  CO 2 + H 2 O 2. AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag 3. Mg + N 2  Mg 3 N 2 4. P + O 2  P 4 O 10

19 Types of Reactions Predicting the Products

20 #1: Synthesis Reactions l synthesize - put together 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  ?

21 Write and balance 1. Ca + Cl 2  2. Fe + O 2  iron (II) oxide 3. Al + O 2 

22 #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

23 #2: Decomposition Reactions l Can predict the products of a binary compound l Made up of only two elements l Falls apart into its elements l H 2 O l HgO

24 #2: Decomposition Reactions l If the compound has more than two elements, you must be given one of the products l NiCO 3 CO 2 + ? l H 2 CO 3 (aq)  O 2 + ?

25 #3: Single Displacement l One element replaces another l Reactants must be an element and a compound. Na + KCl  K + NaCl F 2 + LiCl  LiF + Cl 2

26 #3: Single Displacement Exceptions for transition metals: l Zinc, Zn, always forms a +2 ion l Silver, Ag, always forms a +1 ion

27 #3: Single Displacement l Metals replace metals (and hydrogen) K + AlN  Zn + HCl  l Think of water as HOH l Metals replace one of the H, combine with hydroxide. l Na + HOH 

28 #3: Single Displacement l We can tell whether a reaction will happen using Activity Series. l More active replaces less active l If the element by itself is higher, it happens, if its lower it doesn’t

29 Activity Series of common metals l K l Na l Ca l Mg l Al l Zn l Fe l Sn l Pb l H 2 l Cu l Ag l Au

30 #3: Single Displacement Will it even happen? l Fe + CuSO 4  l Pb + KCl  l Al + HCl 

31 #3: Single Displacement l Nonmetals can replace other nonmetals - Limited to F 2, Cl 2, Br 2, I 2 l F 2 + HCl  l Br 2 + KCl 

32 #4: Double Displacement l Two things replace each other. l Reactants must be two ionic compounds or acids. l Usually in aqueous solution l The positive ions change place

33 #4: Double Displacement NaOH + FeCl 3  Fe +3 OH - + Na +1 Cl -1 NaOH + FeCl 3  Fe(OH) 3 + NaCl

34 #4 Double Displacement l Will only happen if one of the products : –doesn’t dissolve in water and forms a solid –is a gas that bubbles out. –is a covalent compound (usually water)

35 Complete and Balance assume all of the reactions take place. l CaCl 2 + NaOH  l CuCl 2 + K 2 S  l KOH + Fe(NO 3 ) 3  l (NH 4 ) 2 SO 4 + BaF 2 

36 How to Recognize Which Type Look at the reactants: l E + E Synthesis l CDecomposition l E + CSingle displacement l C + CDouble displacement

37 Examples l H 2 + O 2  l H 2 O  l Zn + H 2 SO 4  l HgO  l KBr +Cl 2  l AgNO 3 + NaCl  l Mg(OH) 2 + H 2 SO 3 

38 #5: Combustion A compound composed of only C, H (sometimes O) 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.

39 `Examples l C 4 H 10 + O 2  (complete) l C 4 H 10 + O 2  (incomplete) l C 6 H 12 O 6 + O 2  (complete) l C 8 H 8 +O 2  (incomplete)

40 Chapter 6 Summary

41 An equation l Describes a reaction l Must be balanced because to follow Law of Conservation of Energy l Can only be balanced by changing the coefficients. l Has special symbols to indicate state, and if catalyst or energy is required.

42 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 using activity series. l Double Replacement happens if the product is a solid, water, or a gas.

43 The Process l Determine the type by looking at the reactants. l Put the pieces next to each other l Use charges to write the formulas Use coefficients to balance the equation.