We all know that elements and compounds undergo reactions. In chemistry there are 6 main types of reactions. They are:

• Synthesis
• Decomposition
• Single Replacement
• Double Replacement
• Combustion
• Neutralization

Wow! It seems like it would be a lot to memorize, eh? Well, actually, it's pretty simple! Here's a breakdown of each reaction and a helpful diagram to help you remember!

Synthesis

-A combination of 2+ reactants into a single product. Think of it as a girl and a boy begin dating.
-General form: A + B --> AB

Ex. 2Na + Cl₂ --> 2NaCl
  
Decomposition

-A break down of a single compound into compounds or elements. Think of it as a the girl and the boy breaking up.
-General form: AB --> A + B

Ex. 2HgO --> 2Hg + O₂

Single Replacement

-An element replaces an ion in an ionic compound. Metal elements switch places with cations, which are the positive ions. Non-metals switch places with anions, which are the negative ions. Think of it as a woman stealing another woman's husband! Oh no!
-General forms: AB + C --> AC + B                                         A + BC --> AC + B
                 -this form applies when B & C are anions (-)         -this form applies when A & B are cations (+)

Ex. (metals) 2K + 1CaBr₂ --> 2KBr + 1Ca
    (non-metals) 2BeCl₂ + F₂ --> 2BeF + 2Cl₂

There's one more little rule you need to know about single replacement. Cations cannot replace cations willy nilly, and the same goes for anions. You must look at an activity series sheet to make sure that the replacement can take place.

 

As you can see on the activity series to the left, the elements fall in order. If the element that is doing the replacing is higher up than the element being replaced, the reaction will take place. If the element doing the replacing is lower than the element being replaced, the reaction will not take place.

Ex. 2Na + CaCl₂ --> 2NaCl + 1Ca

              = NO REACTION

You see how in the above reaction, the Na (replacer) is lower than Ca (replacee)? That means the reaction does not occur.

Double Replacement

-Occurs when two ionic compounds switch there cations (positive ions). Think of it as two couples switching their partners!
-General form: AB + CD --> CB + AD
Ex. Cs₂CO₃ + BeCl₂ --> 2CsCl₂ + BeCO₃

Similar to single replacement, there is a rule which must apply to the reaction for the reaction to occur. If a change in state occurs in the reaction, then the reaction will occur (usually a precipitate will form). We can find if there's a change in state by using a solubility sheet.



If the compound is soluble, then no reaction occurs. If the compound is not or low soluble the reaction occurs!

• soluble = bad
• non/low soluble = good

Ex.  2NH₄NO₃(aq) + 1BeBr₂(aq) --> 2(NH₄)Br(aq) + 1Be(NO₃)₂(aq)

You see how in the above example, all the products are aqueous? That means no solid has formed, which means there was no change of state that occurred, therefore there was NO REACTION.

Ex. 2NH₄Cl(aq) + Pb(NO₃)₂(aq) --> 2NH₄NO₃(aq) + PbCl₂(s)

Aha! We have an solid that has formed! That means the reaction has occurred!
Now that we know that reaction took place, we should write a net equation. This is how:

• First step is to write out each ion out seperately. Don't forget to write its charge, its quantity, and its state! The solid solution stays as a whole.

2NH₄⁺_(aq) + 2Cl_2(aq) + Pb^2-_(aq)+ 2NO₃^-_(aq) --> 2NH₄⁺_(aq) + 2NO₃^-_(aq) +  PbCl_2(S)

• Next step is to cross out the same ions that appear twice on the reactants and products side

2NH₄⁺_(aq) + 2Cl_2(aq) + 1Pb^2-_(aq)+ 2NO₃^-_(aq) --> 2NH₄⁺_(aq) + 2NO₃^-_(aq) +  1PbCl_2(S)

• Now that all the duplicates are crossed out, we see what's left. Then we make an equation out if them!

                                                       1Pb^2-_(aq)+ 2Cl_2(aq)--> 1PbCl_2(S)

                                                    And voila! There is our net equation!

Combustion

-When burning in air occurs. Reactants are burned and react with the oxygen in the air.The products are oxygen atoms that are usually combined with other atoms.
-General form: AB + O --> AO = BO

Ex. CH₄ + 2O₂ --> CO₂ + 2H₂O

Neutralization

-similar to double replacement, except the reactants, an acid and base, react and produce an ionic salt and water (H₂O)
Ex.1H₂SO₄ + 1Ba(OH)₂ --> 1BaSO₄ + 2H₂O

So we've covered the basics of the 6 types of reactions! Now you should try applying it to equations! These are great website to check out:
http://www.sciencebugz.com/chemistry/chprbbaleq.html

http://www.youtube.com/watch?v=ul4xRy8hcsQ