Jan 27---Type of Reactions

 Six generalized types of reactions:

- Synthesis

- Decomposition

- Single Replacement

- Double Replacement

- Combustion

- Neutralization

Synthesis

-two or more reactants to form one product        

 Formula: A +B→C

Eg： Mg + Cl2 →MgCl2

Decomposition

-one reactant breaks down into two or more products

Eg: MgCl2 → Mg + Cl2

Single Replacement / Displacement

-an element replaces an ion in an ionic compound: 

Metal elements replace positive ions (cations), non-metal elements replace negative ions (anions)

Formula: A + BC →AC + B (A is metal)

              A + BC → BA + C (A is non-metal)

Eg: 2Li + MgCl2 →2LiCl + 2Al

      Cl2 +2 KF → F2 + 2KCl               

Predicting Single Replacement Reactions:

Some metals are more reactive than other metals, also there are some non-metals are more reactive     

“Active Series” help us to decide whether the equation can react or not.

An element higher up on the series replaces the ion below it on the table.

  

Feb.2--Types or Reactions (Part 2)

Double Replacement: a reaction between two ionic compounds (usually in solution).

AB + CD --> CB + AD

Note: Remember that a metal always combine with a non-metal!

Ex. Na₂CO₃ + CaCl₂ --> CaCO₃ + 2 NaCl

To determine if a double replacement reaction actually occurs, use your “Table of Solubility” to check if the reactants change state. If there is no change of state, the reaction won’t occur.

How To Use the Table of Solubility

Step 1. Find your anion (negative ion) in the left hand column.

Step 2. Find your cation (positive ion) in the second column.

Step 3. Check to see if the compound is soluble or not.

Step 4. If soluble, the compound is (aq); if insoluble, the compound is (s).

Net Ionic Equation

- There is a net reaction when you have a precipitation that occurs.

- (aq) ions that are the same on both sides get cancelled

Ex. 2 Na₃PO₄ + 3 Ca(NO₃)₂ --> 6 NaNO₃(aq) + Ca₃(PO₄)₂(s)

   net ionic equation: 3 Ca²⁺(aq) + 2 PO₄^3-(aq) --> Ca₃(PO₄)₂(s)

Combustion: a reaction where burning in air is involved. The reactants are the chemicals to be burned (organic compound) and the oxygen that it reacts with. They usually produce carbon dioxide and water.

AB + O2 --> AO + BO

Ex. C₄H₈ + 6 O₂ --> 4 CO₂ + 4 H₂O

Neutralization: acid react with base to produce water and an ionic salt. (Double Replacement)

Note: Both acid and base should be aqueous solutions!

HA + BOH --> H₂O + BA

Ex. 2 HBr(aq) + Sr(OH)₂(aq) --> SrBr₂(aq) + 2 H₂O(l)

Jan 25---Balancing Equations

To balance a chemical equation,

number of atoms on the left side = the number of atoms on the right side.

Ex.

             2 ScCl + 3 F2  --  2 F3Sc + 3 Cl2

Step 1. Balance the atoms first

Step 2. Balance the whole group

Step 3. Be systematic---in order

Step 4. elemental form ( K2,Cl2)