UNIT 12: CLASSIFICATION OF CHEMICAL REACTIONS

1

Chemical Reactions• a process that involves changes in the structure and energy content of atoms, molecules, or ions but not their nuclei.

2

Most reactions occur in the aqueous phase (in water) because the particles can move about and interact with each other.

3

Remember This?

• Dissolving- a solvent

surrounds a solute.

Watch This

4

Formation of Solutions -Dissolving• A solute dissolving in a solvent requires energy.

• It can be an endothermic or exothermic process.

Is it a chemical reaction?

5

Formation of Solutions- DissolvingCovalent molecules … • DO NOT break apart when dissolved.

•Ionic Compounds… • DO break apart when dissolved

• (this is considered a chemical change)

6

Molarity• A unit of concentration The number of moles of solute

dissolved in 1.00 L of solution.

Molarity (M) = Moles of solute• Liter of solution

7

Practice Problem• What is the molarity if 2.0 moles of glucose are added to

5.0 L of solution?

8

Practice Problem

• Molarity (M) = Moles of solute Liter of solution

2.0 moles =.40 M

5.0 L

9

How to prepare a solution

10

Grams = Molarity X Liter X Molar Mass of Solutesolute

Watch This

How to prepare a solution

11

To make a concentrated solution more dilute use this formula M1V1 = M2V2

M1 = concentrated solutionV1 = amount of concentrated solution need to make dilute solutionM2= dilute solutionV2 – amount of diluted solution wanted.

Law of Conservation of Matter• matter cannot be created or destroyed, it can only change forms.

• Therefore, in a chemical reaction the number of

atoms, the mass and the charge must be conserved.

Watch Thisreactants

products

Activated complex

12

EQUATIONS

Balancing Equations –

In order to be balanced, the type and number of atoms must match on the reactant and product side

13

Balancing Equations-Taking inventory

(l)22(g)2(g) OH2O H2 Reactants

• 4 hydrogen

•2 oxygen

Products

•4 hydrogen

•2 oxygen

In order to be balanced, the type and number of atoms must match on the reactant and product side

14

Tutorial and Practice

• Tutorial• Watch This

• Practice

15

• __H2S(g) + __SO2(g) __S(s) + __H2O(g)

Reactants Products

16

__Fe2O3(s) + __H2(g) __Fe(s) + __H2O(g)

Reactants Products

17

Types of Reactions• Combination/Synthesis/Composition A + B AB

• Decomposition AB A + B

• Single Replacement C+ AB AC + B

• Double Replacement AB + CD AD + CB

• Combustion CxHy + O2 CO2+ H2O

• Redox – any of the above where the oxidation number of two species changes

18

+

Watch This

19

20

21

22

Double ReplacementClue: Do-See-DohAB + CD AD + CB

23

Combination 1• Also known as composition or synthesis; one product

http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm

___K (s) +___Br2 (l) ___KBr (s)

24

Combination 2

____Zn (s) + ___I2 (l)____ ZnI2 (s)

http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm

25

Decomposition

• Single reactant breaks down into two or more simpler substances

26

Single Replacement• A single element replaces another element in a compound.• Must use activity series to determine if reaction will take place.

More active will replace less active.

___Cu (s)+ __AgNO3 (aq) __Cu(NO3 )2 (aq)+ ___Ag (s)

Remember:

Metal can only replace

metal (or hydrogen)

Nonmetal can only replace

nonmetal

SR animation

27

Using the activity series: Watch This

.For a single replacement to occur, the solo metal must be more reactive than the metal it replaces.

The higher up on the list, the more reactive it is.

28

Single Replacement• For a single replacement to occur, the solo nonmetal must be more reactive than the nonmetal it replaces.

• The higher up on the list, the more reactive it is.

29

Double Replacement• Two reacting compounds, with metals trading places.

• A precipitate (insoluble solid) is formed.

___AgNO3 (aq)+ ____NaCl (s) ____NaNO3 (aq)+ ____AgCl (s)

30

Determining solubility of products

• Use the solubility rules on the back of the periodic table.• The solubility rules are organized by the anion in the

compound.• Find the anion. * this is the negative ion *• Determine if, based on the cation, the compound is

soluble (aq) or insoluble (s) in water.• Write the (aq) or (s) after the compound• Practice:• AgCl

• K(NO3)

• PbS

31

• Solubility Shortcuts – here’s all you need to remember:

• All group 1 metals

• All nitrates (NO3- )

• All acetates (C2H3O2- )

• All ammonium (NH4+ )

ARE ALWAYS SOLUBLE (aq)

Remember HAPStands for Mercury (Hg), Silver (Ag) and Lead (Pb)

Compounds with these elements are usually

INSOLUBLE (s)

32

Try these:NaC2H3O2

Hg(OH)2

MgBr2

(NH4)2SO4

33

Combustion

• _C3H8 + _O2 _ CO2 + _H2O + energy

• A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide.

• It is highly exothermic

.

34

OXIDATION-REDUCTION REACTIONS• a reaction where electrons are transferred between

reactants and products

• Watch This

35

OXIDATION-REDUCTION REACTIONS a. Loss of Electrons is OXIDATION

i. oxidation number increases across the arrow.

b.Gain of Electrons is REDUCTION

i. oxidation number decreases across the arrow.

*LEO the Lion Says GER- These must occur together. Can’t have one without the other.

36

OXIDATION-REDUCTION REACTIONS Oxidation Number (Oxidation State) – a method of

keeping track of electrons gained (reduced) and lost (oxidized).

37

OXIDATION-REDUCTION REACTIONS

Rules for assigning oxidation numbersa. Atoms in their elemental form have an oxidation number of

zero. Cu = 0b. Monatomic ions have an oxidation number equal to their

charge. K+1= +1.c. Nonmetals have negative oxidation numbers.

i. Oxygen is -2 in all compounds with the exceptions of peroxides in which it is -1

ii. Hydrogen is usually +1 with nonmetals Hydrogen is usually -1 with metals

d. The sum of the oxidation number in an neutral compound is zero.

38

OXIDATION-REDUCTION REACTIONSHow to identify a redox reaction.

a. Determine the oxidation number of each element in each compound.

b. Compare the reactants and products.

c.If there is a change in the oxidation number of any species, then it is redox.

d.Number increases across arrow = oxidation LEO

e.Number decreases across arrow = reduction GER

39

OXIDATION-REDUCTION REACTIONSPractice- are the following redox reactions?

______ a. NaCl + AgNO3 --> NaNO3 +AgCl

______ b. FeCl2 + Cl2 FeCl3

40