Type of Reactions PART DEUX

Double Replacement
 
What is double replacement?
It's a reaction with two ionic compounds usually in a solution. It's like a switch partners dance! The ions switch partners. The positive ions switch places.
 
General Formula: 
AB + CD ---> CB + AD
 

In this case, the positive ion (or A) is the brunette girl, the brown-haired guy is B, the blonde girl is the other positive ion (C), and the blonde guy is D. The girls = positive ions. The guys = negative ions. In a double replacement reaction, the positive ions, in this case the two girls, would switch positions and will therefore have different partners. Now, the brunette girl is paired up with the blonde guy (AD), and the blonde girl with the brunette (CB).
 
For ex:
Na2CO3 + CaCl2 ---> CaCO3 + 2NaCl
(remember to balance your equations!) 


BUT how can we find out if the double replacement even occurs???
During the reaction, if the reactants changes its state, then there is a reaction occurring. So if a precipitate (formation of a solid in a solution) forms, then a double replacement reaction occurs. AND IF there is no change of state then obviously that means that there is no reaction.
 
REMEMBER to use your "Table of Solubilities"!! This will determine the states - (s) or (aq)
 
In case you don't know how to use this "Table of Solubilities", i'll just do a little review on that!
 
First: Find the negative ion on the left side of the column.
Second: Look for the positive ion on the second column.
Third: Follow its presence or absense to the word "soluble" or "not soluble''
Fourth: If it's soluble, the compound = aq
Fifth: If it's not soluble, the compound = s
 
Net Ionic Equations
 
??? What is this????
When you have a precipitation that occurs, we write a net ionic equation for the reaction in ionic form to indicate the ionic components that exists in a solution.
(aq) ions that are the same on both sides gets cancelled!
 
For ex:
2Na3Po4(aq) + 3Ca(NO3)2(aq) ---> 6NANo3(aq) + Ca3(PO4)2(s)
the aqueous ions that are equal are cancelled, leaving the ions that forms the precipitate.
Net Equation
3Ca2+(aq) + 2PO43-(aq) ---> Ca3(PO4)2(s)
 
Combustion
 
A combustion is a reaction when a burner in the air is involved. The reactants are the chemical to be burned and the oygen that it reacts with. Oxygen atoms end up combined with more than one type of atom as products.
 
General Formula:
AB + O2 ---> AO + BO
 

 
For ex:
C4H8 + 6O2 ---> 4CO2 + 4H2O
 
Neutralization
 
This is a special DR reaction when acids react with bases to produce water and an ionic salt as a product.
The acids have an H+ as the positive ion and the bases have OH- as the negative ion. Both should be (aw) solutions.
 
General Formula:
HA + BOH ---> H2O + BA
 

 
For ex:
2HBr(aq) + Sr(OH)2(aq) ---> SrBr2(aq) + 2H2O(l)
 
 
 
 
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And that's it!!! 
 
- Melody