Lesson 29 Types of Reactions

Objectives:

-         The student will list the five types of reactions.

-         The student will classify reactions as one or more of the five types.

-         The student will apply an activity series to determine if a reaction will take

place.

 

PA Science and Technology Standards: 3.4.10.A; 3.4.12.A; 3.1.10.C; 3.4.12.B; 3.4.10.B

I.     Combustiona.      Most reactions used for energy are combustion

reactionsb.      Combustion – exothermic reaction that usually

involves oxygen to form the oxides of the elements in a reactant.

c.      Example

                        i.      S8(s) + 8O2(g) 8SO2(g) + energy – this is the reaction which occurs on a match head when it lights

                        ii.      CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + energy – this is the reaction when methane burns

iii. (C6H10O5)20 + 120O2 120CO2 + 100H2O + energy – this is the reaction when

the rest of the paper in the match burns.

d.   Often in combustion reactions, the products listed are not formed, because the reaction doesn’t progress to completion

          i.      Sometimes CO is formed instead of CO2

          ii.     Sometimes all of the carbon is not converted to carbon containing gases – this leaves ashes.

Complete combustion usually requires extremely high temperatures.

Combustion

Hydrocarbon + Oxygen Carbon dioxide + Water

II. Synthesis

a.      Synthesis – the process of building compounds from elementary substances through one or more chemical reactions

b.      The key feature of synthesis reactions is that they are used in building more complex molecules

from simpler ones.

c.      Some reactions, such as the match head lighting above, fit more than one kind of reaction type – this one is both a synthesis reaction and a combustion reaction.

d.     One specific type of synthesis reaction is polymerization

              i.      To make cellulose or starch, a bunch of glucose molecules are attached together in a long chain.

              ii.      Polymerization – a chemical reaction in which many simple molecules combine in chains to form a very large molecule.

               iii.      Repeating simple units are called monomers, and the chains or molecules are called polymers.

               iv.      Plastics, DNA, and the compounds mentioned above are examples of polymers.

               v.      In some cases, the monomers are identical, like in most plastics – in other cases, the monomers are

different, such as in DNA.

Synthesis

A + B AB

III. Decomposition

a.      Decomposition - chemical reaction in which a single compound is broken down to produce two or more simpler substances.

b.      Common products of decomposition reactions are CO2, O2, H2, and N2.

c.      The key feature of decomposition reactions is that the reactant compound is broken down into two or more simpler compounds

Decomposition

AB A + B

III. Single Displacement

a.      Elements trade places in single-displacement reactions (also sometimes known as single replacement reactions)

i.      Single-displacement reaction – chemical reaction in which one element replaces another element in a compound

                        ii.      Examples

      Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

      2Al(s) + 3CuCl2(aq) 2AlCl3(aq) + 3Cu(s)

      2K(s) + 2HOH(l) 2KOH(aq) + H2(g)

b. An activity series summarizes and predicts reactions

         i.      Two examples

      2K(s) + 2HOH(l) 2KOH(aq) + H2(g)

      Cu(s) + 2H2O no reaction

   ii.      Being able to write a chemical equation does not necessarily mean that the reaction will actually take place.

               iii.      In order to determine if a reaction will take place, you must use an activity series.

               iv.      Activity series – an arrangement of elements in the order of their tendency to react with water and acids.

               v.      If an element higher up on the activity series is brought into contact with a compound containing a less active

element, it will replace it in that compound in a single-displacement reaction.

vi.    Example

     * Potassium will replace hydrogen in water because it is higher up on

the list than hydrogen

* Copper will not replace hydrogen in water because it is lower than hydrogen on the list.

vii. The activity series can be used to determine if a reaction will take place.

It is not completely correct, but the exceptions are not worth noting.

viii. You do not need to know the activity series – you need to know how to use it.

c.     Controlling reactions with the activity series

           i.      In general, the farther apart two elements are on the activity series, the more likely the higher

one will replace the lower one in compounds.

            ii.      Also, the greater the difference, the more violent the reaction.

iii. This allows us to control specific reactions by coating certain metals such as iron with

other metals like zinc, since zinc will react faster than iron

Single Displacement

A + BC AC + B

Or

A + BC BA + C

V. Double Displacementa.       In double-displacement reactions, atoms are

exchanged between compounds.

b.      Double-displacement reaction – chemical reaction in which two elements in different compounds exchange places.

c.       Example

i.      2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

d.      The main reason why this reaction occurs is because one of the products, PbI2, is not soluble in water, and falls out of solution.

e.       You can treat these reactions as if the ions are all separated in solution, since this is what happens when these compounds are placed in solution.

f. It would be better to show this reaction as follows:

         i.      2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq)

PbI2(s) + 2K+(aq) + 2NO3-(aq)

            ii.      Note that the K+ and NO3- ions do not actually

participate in the reaction, because they appear in the same form on the left and the right of the reaction.

            iii.      These non-participatory ions are called spectator ions.

            iv.      Often, these reactions can be simplified by not showing the spectator ions, writing what is known as a net ionic equation.

g.  Double displacement reactions always involve the formation either of a molecular compound such as water, or the creation of a gas or a precipitate.

            i.      Combining acids and bases results in a double-displacement reaction

1.      Example

a.       Mg(OH)2(aq) + 2HCl(aq) MgCl2(aq) + 2H2O(l)

b.      This is an example of Mg(OH)2, a base, neutralizing HCl, an acid.

2.      Acid/Base reactions always produce water and a salt.

a.       Net ionic equation – OH-(aq) + H+(aq) H2O(l)

Double Displacement

AB + CD AD + CB

Reaction Summary

Five Classes of Reactions Virtual Lab 2 video

Questions: 1. List the five types of reactions, and define each.2. Indicate which of the five types each of the following reactions is:

a. Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)

b. C6H12O6 + 6O2 6CO2 + 6H2O

c. 2H2 + O2 2H2O

d. 2KI (aq) + Pb(NO3)2 (aq) PbI2 (s) + 2KNO3 (aq)

e. 6CO2 + 6H2O C6H12O6 + 6O2

f. A reaction in which two element exchange places.g. A reaction in which something is burned in oxygen.h. A reaction in which something more complex is built up from several less complex

things.i. A reaction in which one more reactive element replaces one less reactive element in a

compound.j. A reaction in which a complex molecule is broken down into several simple

compounds.k. Having a campfire.l. Plants converting oxygen and water, with energy from the sun, into sugar molecules.m. Humans transforming sugar, in the presence of oxygen, into carbon dioxide and water.

1. Indicate whether a reaction will occur or not in each of the following cases:

a. Li + ZnCl2 ?

b. Ni + CuSO4 ?

c. Cu + AlBr3 ?

d. Ca + KNO3 ?

e. Ba + HgOH ?

f. Au + AgNO3 ?

g. Mg + Ca(OH)2 ?

Reaction Prediction Problems For each of the following reactions, write a complete WORD equation. Beneath the word

equation write a complete balanced equation, substituting chemical symbols for the words.

 Some of the examples will have substances which do not react. Indicate this by writing NR. 1.      potassium plus fluorine 2.      hydrogen plus oxygen 3.      magnesium plus hydrochloric acid 4.      calcium hydroxide plus hydrogen nitrate 5.      sulfur dioxide plus water 

6.      methane (CH4) plus oxygen 7.      copper plus sulfuric acid

8.      aluminum plus hydrochloric acid 

9.      sodium chlorate (heated) 

10.      aluminum plus magnesium 

11.      magnesium plus zinc periodate 

12.      mercury plus oxygen (mercury (II) product formed) 

13.      zinc chloride plus hydrogen sulfide 

14.      silver chloride plus sodium perchlorate 

15.      barium nitrate plus sodium chromate 

16.      sodium bromide plus silver nitrate 

17.  calcium phosphate plus aluminum sulfate 

18.  zinc carbonate (heated)

19.      mercury I sulfate plus ammonium thiocyanate

 

20.      potassium sulfite plus zinc phosphate

 

21.      lithium oxide plus water

 

22.      sodium chloride (electrolysis)

 

23.      iron (II) hydroxide plus phosphoric acid

 

24.      dinitrogen pentoxide plus water

 

25.      sodium plus nitric acid

 

26.      iron (III) iodide plus copper (II) fluoride

27.      lead plus potassium chlorate 

28.      sulfur plus oxygen 

29.      sodium sulfate plus barium chloride 

30.      ammonium phosphate plus lithium hydroxide 

31.      mercury plus nitric acid (mercury (II) product is formed) 

32.      sodium oxide plus water 

33.      mercury (I) sulfate plus hydrochloric acid 

34.      calcium carbonate plus lithium iodide 

35.      bromine plus chlorine 

36.  mercury II nitrate plus sodium dichromate 

37.  water (electrolysis)

38.      cobalt (II) nitrate plus barium hydroxide

 

39.      ammonium sulfate plus calcium hydroxide

 

40.      mercury (II) oxide (heated)

 

41.      ammonium bromide plus aluminum chloride

 

42.      barium oxide plus water

 

43.      tin (IV) hydroxide plus nitric acid

 

44.      calcium plus oxygen

 

45.      magnesium plus phosphoric acid

46.      cadmium chloride plus ammonium hydroxide

 

47.      aluminum sulfide plus acetic acid

 

48.      strontium plus sulfur

 

49.      calcium plus aluminum bromide

 

50.      potassium hydroxide plus sulfuric acid

DEMONSTRATIONS!!

DOUBLE DISPLACEMENT

Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(s)

DECOMPOSITION

2H2O2 2H2O + O2

SINGLE DISPLACEMENT

Zn + 2HCl ZnCl2 + H2

SYNTHESIS

2H2 + O2 2H2O

COMBUSTION!

2C3H8O + 9O2 6CO2 + 8H2O

CH4 + 2O2 CO2 + 2H2O