SYNTHESIS, DECOMPOSITION, AND COMBUSTION Flashcards
Categorizing Chemical Reactions
There are millions of known chemical reactions!
Chemists group reactions into categories to make the prediction of reaction products much simpler
With some exceptions, most reactions can be classified as one of five types, three of which we will cover in this lesson
Combustion
The reaction of a substance with oxygen, producing oxides and energy is called a combustion reaction
Misconception – CO2 (g) and H2O (g) are always produced
Complete Combustion of Hydrocarbons
The complete combustion of a hydrocarbon occurs when the oxygen supply is plentiful.
The products are energy, carbon dioxide, and water vapour
CxHy + O2 –> CO2 + H2O + energy
Complete combustion is the 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)
Balancing Complete Combustion Reactions
Start by balancing the C atoms, then the H, then the O
Balancing Complete Combustion Reactions
Fractions
Sometimes using fractions will save you!
But remember to remove a fraction by multiplying the entire equation by the denominator of the fraction, which will most likely always be 2!!
Incomplete Combustion of Hydrocarbons
Incomplete combustion of hydrocarbons occurs when the supply of oxygen is limited (“fuel-rich” conditions)
Products may include carbon dioxide, carbon monoxide, soot (carbon-rich molecules), water, and energy
Because so many reaction products are possible, incomplete combustion cannot be represented by a single chemical equation
Concerns Related to Incomplete Combustion
Incomplete combustion releases only a portion of the energy that may be obtained from hydrocarbon fuels!
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”
Synthesis Reactions
In a synthesis reaction, two or more reactants combine to form one larger or more complex product
A + B = AB
We can use this pattern to predict the products of a synthesis reaction
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!!!
*Note: these can also be classified as combustion reactions
Metal + Oxygen –> Metal Oxide
Criss-cross charges to form products
These form covalent molecules, so you must draw Lewis structures to determine number of atoms
Metal + Non-Metal –> ?
Binary Ionic Compound!
Criss-cross charges to form products
Metal Oxide + Water…
Base (Metal + OH)
Ionic compounds are usually–> (state)
solid
When a metal carbonate is heated,
it breaks down to produce a metal oxide and carbon dioxide gas.
When a metal nitrate is heated
it breaks down to produce a metal nitrite and oxygen
