05A_Reaction Types.pdf

Reaction Types

Combination Reactions Decomposition Reactions Single Replacement Reactions Double Replacement Reactions

1. Combination Reactions

• Combination reactions occur when two

substances (generally elements) combine and form a compound. (Sometimes these are

called combination or addition reactions.)

reactant + reactant



• Basically: A + B



• Example: 2H₂ + O₂  2H₂O

Combination Reactions

2. Decomposition Reactions

• Decomposition reactions occur when a

compound breaks up into the elements or in a few to simpler compounds

• 1 Reactant



• In general: AB



• Example: 2 H₂O



Decomposition Reactions

3. Single Replacement Reactions

• Single Replacement Reactions occur when

one element replaces another in a compound.

• A metal can replace a metal (+) OR

a nonmetal can replace a nonmetal (-).

• element + compound product + product

A + BC  AC + B (if A is a metal) OR

Single Replacement Reactions

4. Double Replacement Reactions

• Double Replacement Reactions occur when

a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound

• Compound + compound



5. Combustion Reactions

• Combustion reactions

occur when a hydrocarbon reacts with oxygen gas.

• This is also called

Combustion Reactions

• In general:

C_xH_y + O₂  CO₂ + H₂O

• Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)

Identify the Reaction Type

 C₆H₁₂ + O₂



 Pb + FeSO₄



 P₄ + O₂



Identify the Reaction Type

 C₆H₁₂ + O₂



 Pb + FeSO₄



 P₄ + O₂



 MgCl₂ + Li₂CO₃



OXIDATION - REDUCTION

GAIN/LOSS OF OXYGEN LOSS/GAIN OF HYDROGEN LOSS/GAIN OF ELECTRONS

OXIDATION - REDUCTION

2 CO + O

----> 2 CO

 What happens to CO when it reacts to

form CO₂? It gains O, so it is oxidized.

 What happens to O₂ when it reacts to form CO₂? It loses being alone (it is combined), so it is reduced.

H

CO + H

O

--> H

CO

+ H

O

 Which reactant gains O? H₂CO gains O

to become H₂CO₂ , it is oxidized.

 Which reactant loses O? H₂O₂ loses O to become H₂O, it is reduced.

BURNING IS AN OXIDATION

 BURNING IS REACTING A

SUBSTANCE WITH OXYGEN.

 WOOD OR PAPER + OXYGEN --->

WATER + CARBON DIOXIDE

OXIDATION - REDUCTION

CO + 2 H

---> CH

O

 Which reactant gains hydrogen? CO

gains hydrogen to become CH₄O, so it is reduced.

 Which reactant loses hydrogen? H₂

loses being alone (is combined), so it is oxidized.

Oxidation-Reduction in

Biochemistry (Citric Acid Cycle)

 STEP 6 converts succinate to fumarate.  -OOC-CH₂-CH₂-COO- (succinate)+ FAD

---> -_{OOC-CH=CH-COO}-_{(fumarate)+ FADH}

2

 Succinate loses hydrogen, so it is oxidized.

Oxidation-Reduction

We’ll use this one for ionic compounds:

When a metal atom reacts to form a

metal ion - loss of electrons

Li Li

Any element

has an oxidation

number of

zero

The oxidation

number for a

monoatomic

ion is the

charge on the

ion.

When a metal ion reacts to form a

metal atom - gain of electrons

Li

Li

Li

gains

an electron

to become

a Li atom

reduction

The element

Li has an

When a nonmetal reacts to form a

nonmetal ion - electrons are gained.

F - F [ F ]

[ F ]

VE = 14

oxidation

number is

zero

VE = 16

ox. # is -1

for each ion

When a nonmetal ion reacts to form

a nonmetal - electrons are lost.

Fluoride ion

from ionic

compounds

i.e. KF or LiF

F

is the

normal

form of

fluorine.

Oxidation of F

[ F ]

[ F ]

F

2 Li + F

---> 2 LiF

Each Li loses an electron - oxidized.

The F₂ gains electrons - reduced.

F

+ 2 KBr ---> 2 KF + Br

What is oxidized? What is reduced?

F

+ 2 KBr ---> 2 KF + Br

F

is a nonmetal reacting

to form an ion -

reduced

Summary

OXIDATION REDUCTION

GAIN O (COVALENT) LOSE O (COVALENT)

LOSE H (COVALENT) GAIN H (COVALENT)

METAL ATOM TO ION METAL ION TO ATOM

Identify which is oxidized/reduced

 2Al +3Cl₂



 2NiS + 3O₂



AGENTS - causes something else

to make the change.

 Oxidizing agent -causes the other compound to be oxidized by being easily reduced itself.

O

is good oxidizing agent!

 CH₄ + 2 O₂ --->

CO₂ + 2 H₂O

 CH₄ is oxidized.

 O₂ is reduced.

 CH₄ is the

reducing agent.

Driving Forces

Exothermic or Endothermic Entropy (Disorder)

Energy

 Exothermic - when energy is released

by a chemical reaction FEELS HOT

 Endothermic - when energy is required to make the reaction go FEELS COLD

 THE NATURAL DIRECTION OF CHANGE IS EXOTHERMIC.

ENDOTHERMIC REACTION WON’T GO UNLESS ENTROPY IS

ENTROPY MEANS DISORDER

 Entropy increases when a gas is formed

from liquids or solids.

 Entropy increases when a large

compound breaks into many smaller compounds.

Entropy increases, disorder

rules!

 The natural direction of change is toward more disorder. You must do work to

build order.

 A brick wall over