3) Lesson - Synthesis, Decomposition, and Combustion

Question 1

Chemists group reactions into categories to…

Answer 1

make the prediction of reaction products much simpler

Question 2

The reaction of a substance with oxygen, producing oxides and energy is called a…

Answer 2

combustion reaction

Question 3

Misconception of combustion?

Answer 3

CO2 (g) and H2O (g) are always produced

Question 4

Complete Combustion

Answer 4

The complete combustion of a hydrocarbon occurs when the oxygen supply is plentiful.

Question 5

What are the products of complete combustion?

Answer 5

The products are energy, carbon dioxide, and water vapour

Question 6

What are the reactants of complete combustion?

Answer 6

CH +O2–> CO2 + H2O(g) + energy

Question 7

Why is complete combustion the ideal way to burn fuel?

Answer 7

ideal way to burn a fuel because it releases the most energy from the fuel molecules

As a result, complete combustion produces the cleanest (least sooty) and hottest flames (blue)

Question 8

How to balence complete combustion reaction?

Answer 8

Start by balancing the C atoms, then the H, then the O

Question 9

Incomplete combustion

Answer 9

Incomplete combustion of hydrocarbons occurs when the supply of oxygen is limited (“fuel-rich” conditions)

Question 10

What may be the products of Incomplete Combustion

Answer 10

carbon dioxide, carbon monoxide, soot (carbon-rich molecules), water, and energy

Question 11

Can incomplete combustion be repped by 1 equation?

Answer 11

Because so many reaction products are possible, incomplete combustion cannot be represented by a single chemical equation

Question 12

EX of incomplete combustion equation (it is balenced, this is just for refrence. Both equations rep the hydrocarbon for heptane)

Answer 12

C7H16 (l) + 7 O2 –> 3 C (s) + 2 CO2 (g) + 2 CO2 (g) + 8 H2O (g) + energy

OR

2 C7H16 (l) + 15 O2 (g) –> 14CO (g) + 16 H2O (g) + energy

Question 13

What are the three conerns with incomplete combustion

Answer 13

1. releases only a portion of the energy that may be obtained from hydrocarbon fuels! Thia results in not producing and using the max amount of energy
2. Soot particles from incomplete combustion are an inhalation hazard. Many of the chemicals in soot are toxic.
3. Carbon monoxide produced during incomplete combustion is also an inhalation hazard – the “silent killer”

Question 14

Why shouldn’t you bbq inside or start your car inside the garage when the garage door is closed or barely open

Answer 14

• In a closed garage there will be limited O2 even with the garage door slightly open as a result if you’re bbq or starting up your car carbon monoxide will be produced. We know incompletet combustion starts with a lack of oxygen and when you’r epreforming these activites ina closed space with not much O2 carbon monoxide builds up

Question 15

synthesis reaction

Answer 15

two or more reactants combine to form one larger or more complex product

A + B –> AB

Question 16

What are the 5 types of synthesis reactions?

Answer 16

1) Metal/Non-metal + Oxygen
2) Metal + Non-Metal
3) Metal Oxide + Water
4) Non-Metal Oxide + Water
5) Non-Metal Oxide + Metal Oxide

Question 17

Metal/Non-Metal and Oxygen 🡪 Oxide

Answer 17

Synthesis Reactions

(these can also be classified as combustion reactions)

Metal + Oxygen 🡪 Metal Oxide
Criss-cross charges to form products

Ex: 4Al (s) + 3O2 (g) –> 2 Al2O3 (s)

Question 18

Metal/Non-Metal and Oxygen 🡪 Oxide
(non-metal version)

Answer 18

Synthesis Reactions

Non-metal + Oxygen 🡪 Non-metal Oxide

These form covalent molecules, so you must draw Lewis structures to determine number of atoms

EX: 2 S (s) + 3 O2 (g) 🡪 2 SO3

Question 19

2) Metal + Non-Metal 🡪 Binary Ionic Compound

Answer 19

Criss-cross charges to form products

Ex. 2 Al (s) + 3 S (s) 🡪 2 Al2S3 (s)

Question 20

3) Metal Oxide + Water 🡪 Base (Metal + OH-)

Answer 20

Criss-cross charge of metal from the oxide with hydroxide

Li2O (s) + H2O(l) 🡪 2LiOH

Question 21

Basic (Metallic) Oxides
- calcium oxide

Answer 21

CaO (s) + H2O (l) –> Ca(OH)2 (aq)

Used to counteract the effects of acid rain by adding it to acidified lakes or soil!
- By addung the basice and acid together it neutralizes the impatc, the calcium oxide being the base

Question 22

Use of Na2O (s) + H2O (l) –> 2 NaOH(aq) + energy

Answer 22

• most commonly known and sued bases in cleaning products

Question 23

4) Non-Metal Oxide + Water 🡪 Oxyacid

Answer 23

Criss-cross charges of hydrogen w/ “-ate” polyatomic

EX: CO2 (g) + H2O(l) 🡪 H2CO3 (aq)

Question 24

SIGNIFGANCE OF EX: CO2 (g) + H2O(l) 🡪 H2CO3 (aq)

Answer 24

Ocean Acidification!

The CO2 (g) comes from the combustion of fuel which then reacts with the H20 (such as rain, rain is slightly acidic) as a result it causes H2CO3 (the ocean acidifcation

Question 25

Whats the signifgance of SO3 (g) + H2O(l) 🡪H2SO4 (aq) and the type of synthesis reaction?

Answer 25

• 4) Non-Metal Oxide + Water 🡪 Oxyacid

Signifgance is that H2SO4 is Acid Rain!

-Sulfur comes from industries and then reacts with O making SO3 which then combines with H20 (Rain) to make H2SO4 (acid rain)

Question 26

Acidic (Non-Metallic) Oxides

Example: nitrogen oxides

Answer 26

1. N2 + O2 = 2 NO <— occurs in the engine of cars
2. 2 NO + O2 = 2 NO2 <—- No2 contributes to smog
3. 2 NO2 + H2O (l) = HNO3 (aq) + HNO2 (aq)

Question 27

How do catlytic convertors help with limiting smog?

Answer 27

Converter is coated with beads of platinum, palladium, or rhodium catalyst

2 NO – (catalyist speeds up reaction and breaks 2 NO down) –> N2 + O2

Question 28

Acidic (Non-Metallic) Oxides

Example: sulfur oxides

Answer 28

1. S (s) + O2 (g) –> SO2 (g)
2. 2SO2 (g) + O2 (g) –> 2 SO3 (g)
3. SO3 (g) + H2O (l) –> H2SO4 (aq) ( extra acidic rain, which is an enviromental issue)

Question 29

Oxides can be either….

Answer 29

acidic or basic

Question 30

Acidic Oxide

Answer 30

An oxide that forms an acidic solution when dissolved in water; a non-metallic oxide

ex. CO2, NO, NO2, SO2, SO3, etc.

Question 31

Basic Oxide

Answer 31

An oxide that forms a basic solution when dissolved in water; a metallic oxide

ex: MgO, Na2O, CaO, etc.

Question 32

5) Non-Metal Oxide + Metal Oxide 🡪 Salt of Oxyacid

Answer 32

Synthesis Reactions

Note: This reaction is similar to #4 (non-metal oxide + water), except that the metal takes the place of hydrogen in the previous examples
Criss-cross charges of metals w/ the “-ate” polyatomic

Ex. CO2 (g) + Na2O (s) 🡪 Na2CO3

Question 33

Decomposition Reactions

Answer 33

chemical reaction in which one large compound breaks down or decomposes into two or more smaller substances is called a decomposition reaction

AB–> A + B

If you know all the types of synthesis reactions, then you know all the types of decomposition reactions!