3) Lesson - Synthesis, Decomposition, and Combustion Flashcards
Chemists group reactions into categories to…
make the prediction of reaction products much simpler
The reaction of a substance with oxygen, producing oxides and energy is called a…
combustion reaction
Misconception of combustion?
CO2 (g) and H2O (g) are always produced
Complete Combustion
The complete combustion of a hydrocarbon occurs when the oxygen supply is plentiful.
What are the products of complete combustion?
The products are energy, carbon dioxide, and water vapour
What are the reactants of complete combustion?
CH +O2–> CO2 + H2O(g) + energy
Why is complete combustion the ideal way to burn fuel?
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)
How to balence complete combustion reaction?
Start by balancing the C atoms, then the H, then the O
Incomplete combustion
Incomplete combustion of hydrocarbons occurs when the supply of oxygen is limited (“fuel-rich” conditions)
What may be the products of Incomplete Combustion
carbon dioxide, carbon monoxide, soot (carbon-rich molecules), water, and energy
Can incomplete combustion be repped by 1 equation?
Because so many reaction products are possible, incomplete combustion cannot be represented by a single chemical equation
EX of incomplete combustion equation (it is balenced, this is just for refrence. Both equations rep the hydrocarbon for heptane)
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
What are the three conerns with incomplete combustion
- 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
- Soot particles from incomplete combustion are an inhalation hazard. Many of the chemicals in soot are toxic.
- Carbon monoxide produced during incomplete combustion is also an inhalation hazard – the “silent killer”
Why shouldn’t you bbq inside or start your car inside the garage when the garage door is closed or barely open
- 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
synthesis reaction
two or more reactants combine to form one larger or more complex product
A + B –> AB
What are the 5 types of synthesis reactions?
1) Metal/Non-metal + Oxygen
2) Metal + Non-Metal
3) Metal Oxide + Water
4) Non-Metal Oxide + Water
5) Non-Metal Oxide + Metal Oxide
Metal/Non-Metal and Oxygen 🡪 Oxide
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)
Metal/Non-Metal and Oxygen 🡪 Oxide
(non-metal version)
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
2) Metal + Non-Metal 🡪 Binary Ionic Compound
Criss-cross charges to form products
Ex. 2 Al (s) + 3 S (s) 🡪 2 Al2S3 (s)
3) Metal Oxide + Water 🡪 Base (Metal + OH-)
Criss-cross charge of metal from the oxide with hydroxide
Li2O (s) + H2O(l) 🡪 2LiOH
Basic (Metallic) Oxides
- calcium oxide
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
Use of Na2O (s) + H2O (l) –> 2 NaOH(aq) + energy
- most commonly known and sued bases in cleaning products
4) Non-Metal Oxide + Water 🡪 Oxyacid
Criss-cross charges of hydrogen w/ “-ate” polyatomic
EX: CO2 (g) + H2O(l) 🡪 H2CO3 (aq)
SIGNIFGANCE OF EX: CO2 (g) + H2O(l) 🡪 H2CO3 (aq)
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
Whats the signifgance of SO3 (g) + H2O(l) 🡪H2SO4 (aq) and the type of synthesis reaction?
- 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)
Acidic (Non-Metallic) Oxides
Example: nitrogen oxides
- N2 + O2 = 2 NO <— occurs in the engine of cars
- 2 NO + O2 = 2 NO2 <—- No2 contributes to smog
- 2 NO2 + H2O (l) = HNO3 (aq) + HNO2 (aq)
How do catlytic convertors help with limiting smog?
Converter is coated with beads of platinum, palladium, or rhodium catalyst
2 NO – (catalyist speeds up reaction and breaks 2 NO down) –> N2 + O2
Acidic (Non-Metallic) Oxides
Example: sulfur oxides
- S (s) + O2 (g) –> SO2 (g)
- 2SO2 (g) + O2 (g) –> 2 SO3 (g)
- SO3 (g) + H2O (l) –> H2SO4 (aq) ( extra acidic rain, which is an enviromental issue)
Oxides can be either….
acidic or basic
Acidic Oxide
An oxide that forms an acidic solution when dissolved in water; a non-metallic oxide
ex. CO2, NO, NO2, SO2, SO3, etc.
Basic Oxide
An oxide that forms a basic solution when dissolved in water; a metallic oxide
ex: MgO, Na2O, CaO, etc.
5) Non-Metal Oxide + Metal Oxide 🡪 Salt of Oxyacid
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
Decomposition Reactions
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!
