Chem Equations
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Transcript of Chem Equations
Chemical EquationsThat’s what it’s ALL about
Grooooovey baby…yeah!!
What is a chemical equation? It is a symbolic representation of a chemical
reaction, that is balanced and represents the states of matter
That’s soooo exciting!…yeah ok, not really
And I want to know this because…… It is good to know whether a reaction will
take your face off BEFORE you actually throw the chemicals together
Still not sure I get the concept
Think of chemical equation in the
same way that you might think of
a recipe for chocolate chip cookies.
You have ingredients, then you
prepare them, then you get cookies
Can I get my cookies with some Frikin’
Chocolate “chunks?”
Yummy!!!
Ingredients -----------> Bake ----------->Cookies
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
2 1/2 (1 ounce) squares unsweetened chocolate
1/2 cup butter
2 cups all-purpose flour
1/2 teaspoon baking soda
1 teaspoon baking powder
1/4 teaspoon salt
1 1/4 cups white sugar
2 eggs
1 teaspoon vanilla extract
2/3 cup sour cream
2 cups semisweet chocolate chips
--------------------->
It isn’t different in Chemistry… You just don’t eat the cookiesIngredients -----------> Bake -----------> Cookies
Chemistry:
Reactants ------------------------------> Products
Example: O2 + H2 ----------------> H2O (+ enough energy to melt your face)
What happened to the other Oxygen????
yields
Law of conservation of matter
Matter can not be created nor destroyed by ordinary chemical processes
So we have to balance the previous equation
Using coefficients OONNLLYY!!!!!!!!!!!!O2 + H2 ----------------> H2O
ONCE AGAIN….
COEFFICIENTS
ONLY!!!!!!!!!
Here is how this equation looks balanced:
O2 + 2H2 ----------------> 2H2O
How do I balance an equation?The basic concept is to use coefficients ONLY to
be sure that there are the same number of moles of stuff on the left side as there are on the right.
This can be done by counting single elements on both sides and look for lowest common factors
This could get a bit tedious…are there some shortcuts?
Yes: Look for polyatomic ions common on both sides
and treat them as one element Look for lowest common factors to determine
the correct coefficients ALWAYS double check when you are done!!!!
Anything else I need to know about equations??
Oh YEEEES! States of matter of each reactant and
product Reaction types and other CRAPO(N) Metal activity Nonmetal activity Solubility Endo/Exothermic
STATES OF MATTER OF REACTANTS AND PRODUCTS
Since some chemicals react differently (or are more dangerous) when they are liquids, solids, or gasses, it is useful to determine this ahead of time Greenhouse solids would
be a lot better than greenhouse gasses
HERE ARE THE MOST COMMON WAYS TO EXPRESS STATES OF
MATTER
SOLID (s) LIQUID (l) GAS (g) AQUEOUS (DISSOLVED IN WATER) (aq) CRYSTALLINE (cr)There are one or two other obscure ones but these are the
real important ones
Here is how they are used
O2(g) + 2H2(g) ----------------> 2H2O(l)
That is sooo clever!!!
THIS IS A BUNCH OF….
CRAP!!!!
ACTUALLY…IT’S:C R A P O (N)O E C R R UM D I E G CP O D C A LL X B I N EE A P I AX S I C R
I E TO AN T
E
THAT’S RIGHT….ALL CHEMICAL REACTIONS CAN ACTUALLY BE CLASSIFIED AS
CRAPO
(NUCLEAR IS NOT CLASSIFIED AS CHEMICAL)
UNFORTUNATELY, THIS IS NOT THE TRADITIONAL WAY TO CLASSIFY EQUATION TYPES….
I KNEW IT!!
EQUATION (REACTION) TYPES SYNTHESIS
To Put Together or Produce
A + B -------> AB
Example:
H2 + O2 -----------> H2O
Can you see that this is a “putting together” process?
DECOMPOSITION
TO BREAK DOWN
AB -----------> A + B
EXAMPLE:
H2O2 -----------> H2O + O2
CAN YOU SEE THAT THIS IS BREAKING DOWN?
SINGLE DISPLACEMENT (REPLACEMENT)
TO REPLACE A SINGLE ION WITH ANOTHER
AB + C ------------> AC + B (OR CB + A)
EXAMPLE:
HCl + Mg ----------> MgCl2 + H2
Can you see that C has replaced A in the equation?
DOUBLE DISPLACEMENT (REPLACEMENT)TO SWAP TWO CATIONS OR TWO
ANIONS AB + CD ----------> AD + CB
EXAMPLE:
NaOH + H2SO4 -------> HOH + Na2SO4
Can you see that the two cations have switched places?
(ORGANIC) COMBUSTIONTO COMBUST A CARBON-BASED COMPOUND
(USUALLY HYDROCARBON) WITH O2 TO FORM CO2 AND H2O
CXHX + O2 ---------> H2O + CO2
EXAMPLE:
C2H6 + O2 ---------> H2O + CO2
CAN YOU SEE THE HYDROCARBON REACTING WITH OXYGEN AND MAKING CARBON DIOXIDE AND WATER?
From now on… We will refer to CRAPO(N) as Classes of
reactions
And Synthesis, Decomposition, Single displacement, Double displacement, and combustion as equation types
ACTIVITY SERIES!!!!!
Do reactions occur every time chemicals are put together?
Of course not…if they did we would change every time we came in contact with another chemical
Help me!!I’m melting
When a single element is reacting with a compound
The reaction can only occur if the single element is more active than the anion or cation in the compound that it is replacing
Bottom line: the most active elements will be in the bond.
Example
NaOH + Pb -----------> ?
Na is more active than Pb
Will Pb replace Na?
NO!!!!!!!!
Remember the most active elements will be in the bond
Example
K + Cu(OH)2 ----------->?
K is more active than Cu
Will THIS reaction occur?
You Bet!!!!
K + Cu(OH)2 -----------> KOH + Cu
Now we balance it and add the states of matter:
VOILA!!!
2K(s)+ Cu(OH)2(aq) ---------> 2KOH(aq) + Cu(s)
Do I need to memorize the activity series?
NO: Cation activities (mostly metals) are determined experimentally, so you will have a chart, and anion activity series is mostly determined by electronegativity, and this is mainly with the Halides (Halogens) only.
Activity series for metals
LiKBaSrCaNaMgAlMnZnFeCdCoNiSnPbHCuAgHgAu
The metals on top Are more active Than the onesBelow it
Activity series for nonmetals
Simple: Since halides are involved in most replacement type reactions, just remember that the halide higher up on the periodic table will replace the one below it, or in other words the higher, the more active
SOLUBILITY
Have you noticed, in some reactions, that solids form when you mix 2 aqueous chemicals? How is this possible?
Easy: Sometimes chemicals form in a reaction that don’t dissolve in water…they are insoluble-solid
Solubility Definitions
Soluble: Will or is dissolved in a solvent (usually water)
Insoluble: Will not or isn’t dissolve in a solvent
Precipitate: A solid formed from the mixing of two aqueous liquids
More Definitions
Solute: A substance which is dissolved in a solvent
Solvent: A substance which dissolves another substance
Saturation: The formation of more soluble product than a solution can hold at a particular temperature and pressure
How do I know what makes a precipitate?
Compounds containing the following are generally soluble in water
1) Alkali metal ions, and ammonium ions2) Acetate ions3) Nitrate ions4) Halide ions except with: Ag+, Hg2+, and Pb2+
5) Sulfate ions, except with: Sr2+, Ba2+, Pb2+
More Solubility RulesCOMPOUNDS WITH THE FOLLOWING ARE GENERALLY INSOLUBLE IN WATER
6) Carbonate ions (Unless any are paired with those in rule one, which makes these soluble)
7) CrO42- Chromate ions (Unless any are paired with those in rule one,
which makes these soluble)8) Phosphate ions (Unless any are paired with those in rule one,
which makes these soluble)9) sulfide ion (Unless any are paired with those in rule one, which
makes these soluble, as does CaS, SrS, BaS)10) Hydroxide ions (Unless any are paired with those in rule one,
which makes these soluble, as does Ca(OH)2, Sr(OH)2, and Ba(OH)2 here)
PRACTICE-Write the products and predict the precipitate
AgNO3 + NaOH ----->
NH4OH + Na2CrO4------->
ANSWERS
AgNO3 + NaOH -----> AgOH + NaNO3
NH4OH + Na2CrO4-----> (NH4)2CrO4 + NaOH
Blue indicates the insoluble precipitate
CONGRATULATIONS
YOU ARE NOW EXPERTS IN CHEMICAL EQUATIONS!!!
You can use this information for Evil…
Release the “CO2” to start the “global Warming”
Or For Good…. Green is Groovey Baby…Yeah!!!!