Stoichiometry--By Nemo Jin

Definition:

--ratio between the amount of reactants and the amount of products produced by the reactants in a chemical reaction.

--it is based on the fact that all atoms are conserved in a chemical reaction.

Calculation:

Question: 

How many moles of Cl2 are needed to produce 3.4 moles of NaCl in the chemical reaction which sodium metal and chlorine gas combine to form solid sodium chloride?

Step 1:

Write a balanced equation.

2 Na(s) + Cl2(g) --> 2NaCl(s)

Step 2:

Find the ratio for NaCl to Cl

Cl2/NaCl = 1/2

Step 3:

Convert into NaCl

3.4 moles NaCl x 1 mole of Cl2/2 moles of NaCl = 1.7 moles of Cl2

Excess and Limiting Reactants By Sally Chen

The green reactant is the excess quantity,
whereas the red one is the limiting reagent.

- Reactions do not take place exactly as how they are described in balanced chemical equations.
       -Reason:  conditions necessary for the reaction to take place may not be present (ie. pressure, temperature, concentration, etc.)
- It is necessary to add more of one reactant than the amount we get from stoichiometry calculations.
       -Reason:  it is impossible for every atom/molecule of the reactants to come together.
- Limiting Reactant/Reagent:  the ONE reactant that is used up in a chemical reaction.
- Excess Quantity:  the reactants that are left over.

- How much of the excess quantity is left?
       Steps: 1. balance equation
                 2. convert grams of reactant #1 to grams/moles of product #1
                 3. convert grams of reactant #2 to grams/moles of product #2
                 4. compare the answer u get from 2 and 3, the lower one is the amount that will be produced.
                 5. calculate the grams of the excess reactant needed in this reaction.
                 6. calculate the difference between grams of the actual grams of the excess reactant provided and # you get form step 5.

Types of Reaction (including activity series and solubility) -- By Nemo Jin

Energy Diagrams and Calculations--By Tina Zhao

Energy Diagrams:
















Important Terms:








Energy of reactants: Total potential energy of all reactants in the reaction




Energy of product: Total potential energy of all products in the reaction




Energy of the activated complex: potential energy of the "transition state" between reactants




and products.




Activation energy: The energy that must be added to get the reaction to progress




Enthalpy: It is the energy of products - energy of reaction 




There are some examples




（http://www.sciencegeek.net/Chemistry/taters/energydiagram.htm）


















Energy in the Equation






- The energy absorption or release can be placed directly in the equation.




Exothermic : Reactions have the energy term on the right hand side and a negative H




example: CH4 + 2O2 ------CO2 + 2H2O + 812KJ






Endothermic: Reaction have the energy term on the left hand side and a positive H




example: I2 + Br2 + 81.5KJ -------2IBr










Energy Calculations




- The value of H change of a reaction and is expressed in KJ per mole of one of the chemical.
- We ignore the negative in conversion calculation because we use words




example: Using the follow reaction, how many moles of CH4 are needed to produce 2100KJ 




of energy? 










CH4 + 2O2 ------- CO2 + 2H2O + 812 KJ








2100KJ x 1mole of CH4 / 812KJ = 2.6moles of CH4

Endothermic/exothermic Reaction -- by Ria Park

All chemical reactions make changes in energy. Those are:

  Endothermic Reaction:

• This reaction absorbs energy.
• e.g. one ice pack melts. -> it absorbs energy so that ice becomes water.
• It takes more energy to break bonds.

  Exothermic Reaction:

• This reaction release energy.
• 2 explosion explode. -> it release energy.
• It takes takes less energy to break bonds.

> Chemical bonds hold molecules together.

• add energy to break bonds
• lose energy to to join together again.

> Enthalpy(H) is the heat contained in the reactions.

http://www.youtube.com/watch?v=1B3bb9d3WOk

Balancing Equation --By Tina Zhao

Balancing Equation:
- The aim of balancing equation is to make the number of atoms of each kind on the reactant side equal to those on the product side. 


Rule:
-Chemical formulas of reactants are listed on the lefthand side of the equation. 
-Products are listed on the righthand side of the equation. 
-Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions. 
- First balance the atoms which only occur in one molecule on each side of equation
Balance whole group whenever possible, rather than considering the atoms of groups separately
- Be systematic: do not jump all over an equation balancing a bit here and bit these
-balance atoms which occur in elemental from last. By elemental form we mean that the atoms are not combined with atoms of a different kind.

Example for balancing equation:

step 1:

step2:

step3:

step4:

http://www.files.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.htm

http://www.sciencegeek.net/Chemistry/taters/EquationBalancing.htm

http://misterguch.brinkster.net/PRA008.pdf

Open these links, these links may help you for balancing equation. 

Ionic Compound:

Ionic compounds are basically defined as being compounds where two or more ions are held next to each other by electrical attraction. One of the ions has a positive charge (called a "cation") and the other has a negative charge ("anion").I

example:

NaCI :  Sodium Chloride

K2SO4：potassium Sulphate

FE2O3:  Iron(III）Oxide

Covalent Compound:

-Bonding between non-metals consists of two electrons shared between two atoms. 

Mono: 1 Di:2  Tri:3 Tetra:4 Penta: 5 Hexa:6 Hepta:7 Octa:8 Nona:9 Deca:10 Hendeca:11 Dadeca:12

Translating word equations/naming compounds -- by Ria Park

Sometimes we need to translate balancing equations into word equations. There are some rules that they have to follow.

For ionic compounds:
NaCl -> Sodium Chloride
MgCl₃ -> Magnesium Chloride
Fe₂O₃-> Iron(Ⅱ) Oxide

• Put '-ide' at the and of the names of non-metals

For Covalent Compounds:
mono  1
di        2
tri        3
tetra    4
penta  5
hexa   6                      >> Put any of these infront of the names of non-metals
hepta  7
Octa   8
nona   9
deca   10
hendeca  11
dodeca    12

CO₂Carbon dioxide
CO   carbon monoxide


Acids:
HCl  Hydro chloric acid
H₂SO₄Sulfuric aicd
H₂SO₃Sulfurous acid
HNO₃Nitric acid

•  --ate -> --ic
• --ite -> --ous

E.g.

1.  Cu + 2AgNO₃-> Cu(NO₃)₂+ 2Ag  ==>> Copper + silver nitrate -> copper nitrate + silver
2. Cu + I -> CuI ==>> Copper + Iodine -> Copper Iodide
3. C₃H8 + O₂ -> CO₂+ H₂O ==>> Trioxide Octahydride -> Carbon dioxide + water