BALANCING
EQUATIONS!
And so much more!
Chemical Reactions
◦ A chemical reaction happens when chemicals come in contact with one another & collide together with
enough energy to cause the breaking of “old” bonds and the formation of “new” bonds with greater
stability.
◦ A chemical reaction can be written as a sentence
◦ The starting materials are called the reactants.
◦ The new substances created during the chemical change are called products.
◦ Because matter can not be created or destroyed during a chemical reaction, all chemical reactions must be
balance. A BALANCED EQUATION means there are the same number and type of atoms on both sided
of the arrow.
REACTANTS ----------- PRODUCTS
Chemical Reactions
◦ Chemical reactions can be written as sentences!
◦ Example:
◦ Two moles of Hydrogen gas plus one mole of Oxygen gas react to produce two moles of Water
◦ Chemical reactions more often are written in symbol form because it is shorter and simpler to read from the
chemistry point of view!
◦ 2 H2
+
1O2 -----
2 H 2O
◦ THE COEFFICIENTS IN A BALANCED EQUATION REPRESENTS MOLES!
Diatomic Gases
◦ To write correct Balanced Equations (you will be PRO in no time!)
◦ You need to be able to correctly write and name chemical formulas and know the 7 Elemental gases on the
Periodic Table that are DIATOMIC GASES.
◦ Diatomic Gases are elemental gases that always travel with a partner!
◦ F2, Cl2, N2, O2, H2, Br2, I2
◦ When I was a student in high school we learned a “saying” to remember these gases:
◦ Flunk Chemistry NNNOOOHHHHH! Because I’m intelligent
◦ You just have to know that the list of the seven diatomic gases is on the back of your Periodic Table!
Types of Reactions
◦ Chemists are happiest when everything is well organized and clearly described! Its who we are!!!!!
◦ Sooooo……chemical reactions are placed into 5 general Types of Reactions.
◦ Synthesis,
Decomposition,
◦ Double Displacement.
Combustion,
Single Displacement,
Synthesis
◦ Synthesis is the type of reaction where simple substances bond together to create something more complex.
◦ Simple +
simple ------- complex
◦ Or
◦ Element +
Element ----- compound
◦ Examples:
◦ 2 H2 +
1 O2 ------- 2 H2O
◦ 1 N2 +
3 H2 -------
2NH3
Decomposition
◦ Decomposition is the type of reaction where complex substances break down into simpler substances. (yes it
is the opposite of synthesis!)
◦ Complex
------
simple
+
simple
◦ Compound
------ element
+
element
◦ Example: 1 C6H12O6
+ 6 O2 ------
6 CO2
◦ Example: 2 Fe2O3
-------- 4 Fe
+
+
3 O2
6H2O + heat
Combustion
◦ Combustion reactions are the easiest to recognize ( And this type is my personal favorite reaction so….expect
many example of these on tests and quizzes!)
◦ Carbon containing substance plus oxygen gas will produce carbon dioxide plus water plus heat!
◦ These reactions always release energy and in case you forgot that is a.k.a. an EXOTHERMIC reaction.
◦ Example:
◦ 1 CH4
+ 2 O2 -------- 1 CO2
+
2 H 2O
+ Heat:
◦ 1 C4H10
+ 6.5 O2 ------ 4 CO2
+
5 H 2O
+ Heat (2,13,8,10)
+ 12.5 O2 ------ 8 CO2
+
9 H2O
+ Heat (2,25,18,16)
1 C8H18
That’s right three beautiful combustions! The combustion of methane. The combustion of butane. And the
combustion of octane.
Single Displacement
◦ Single displacement reactions have the format:
◦ element
+
compound ------ “new” element
+
“new” compound
◦ Two similar substances are competing for the “attention” of the opposite substance……
◦ Example two metals competing to be with a non-metal or two non-metals competing to be with a metal….
◦ This crazy scenario can be likened to yes…….. a “LOVE” triangle……
◦ The activity Series on the back or your periodic table will allow you to predict who the lucky chosen
substance is that wins the hand of the desired substance and gets to be part of the compound………….
More: Single Displacement
◦ Zinc
+
CuCl2
---- ? (Yes) ZnCl2
+
Cu
◦ Zinc and copper are both metals! They both are very attracted to chloride…… because Zn is “higher” on
the activity table chloride will choose to bond with zinc and leave poor copper alone again as an element
◦ Fe
+
NaCl
----------- no reaction. Sodium is most reactive and already in a compound!
◦ Mg
+
ZnCl2
------------ MgCl2
+
Zn
Double Displacement
◦ Double Displacement Reaction - compound plus compound reacts to create a new compound plus new
compound. It is important to remember to keep the “new” positive w\ negative and that you check charges
and put in correct subscripts.
◦ compound
+ compound
◦ 1HCl
1NaOH ---------
1HOH water
+
1Al2O3
3K2O
1Al2S3
+
◦ 3 K 2S +
-------
------------
“New” compound
+
+“New” compound
1NaCl
Molarity
◦ Important information
◦
◦ * There are 1000 ml in 1 liter.
◦ * The higher the molarity value, the stronger the solution.
◦ * Solute refers to the substance being dissolved.
◦ * You should wear goggles when preparing solutions.
◦
◦ FORMULA
MOLARITY = moles of solute/ liters of solution
“From Scratch” Formula
◦ Example: Molarity= moles solute / liters of solution
◦ Describe how to prepare 2.00 liters of .75 M MgSO4 solution.
◦ M=moles MgSO4/Liters of solution
◦ M= .75= X/2.00 liters cross multiple and solve for “x”.
◦ “x” = 1.5 mole MgSO4
◦ Change moles to grams using dimensional analysis, so you know how much to scoop out of the bottle!
◦ 1.5x 120.38 grams (the molar mass of MgSO4)= 180.57 grams MgSO4 are needed for the solution.
Suit up with goggles and apron! Place 180.57 grams MgSO4 into a clean dry container, add enough water to
create 2.00 liters of solution. DONE!
Dilution Formula
◦ The “1” in the formula represents the initial or strong solution/ the “2” represent the new weaker solution
that you are trying to make.
◦ The symbol M stands for the word Molarity.
◦ Molarity is defined as the strength of a solution in moles of solute per liter of solution.
◦ The symbol V stands for the word volume of solution.
◦ Volume can be measured in milliliters or liters but both volumes in one example must be the same units.
◦ * There are 1000 ml in 1 liter.
To find the water that must be added you do a simple subtraction!
◦ V2 –V1= H2O needed
◦ * Always pour Acid into Water
* You should wear goggles when preparing solutions.
◦
◦ FORMULA
(M1) (V1) = (M2) (V2)
◦
Dilution Example:
◦ Example: Explain how to prepare 3.0 liters of 1.75M Ca(OH)2 form a Stock bottle labeled 6.0 M Ca(OH)2.
◦ (M1) (V1) = (M2) (V2) (6.0M) (X) = (1.75M) (3.0L) so…6x = 5.25 solve for x by dividing both side of the
expression by 6.
“x” = .875 liters of 6.0M Ca(OH)2.
◦ Final step! V2 – V1 = volume of water needed so…..3.0 liter- .875 liters = 2.125 Liters of Water!
◦ Wear goggles and apron. Label container the appropriate label. Pour 2.125 liters of water into the container
then carefully and slowly add .857 liters of 6.0 M Ca(OH)2. Wash your hands! DONE!
Thank you for working hard!
◦ Chapter 8 and Molarity TEST will be before vacation!