Download Reactions (The Basics)

Warm Up: Determine the name and molar mass of the
following compounds.
MnO2
H2SO4
1
How did you do?
MnO2- 86.94 g/mol, Manganese (IV) oxide
H2SO4 98.09 g/mol, Sulfuric acid
Be sure you go back and review the
basics…
2
Warm Up Use percent composition to determine the
amount of chlorine produced in the
decomposition of 402.3 g of calcium
chloride.
BALANCING
EQUATIONS &
CHEMICAL REACTIONS
Evidence of Chemical Change





Changes in Energy (E)
Release of E as heat
Release of E as light
Production of sound
Reduction or increase of
temperature
Absorption or release of
electrical Energy
Formation of new
substances
 Formation of a gas
 Formation of a
precipitate
 Change in color
 Change in odor
Important stuff!
Four abbreviations are
used to indicate
physical states of
chemicals: shown as
subscripts in the chemical
equation
(s) = solid
(l) = liquid
(g) = gas
(aq)= aqueous solution
(dissolved in water)
Symbols over the arrow
indicate the conditions of
the reaction
Heat
Pressure
Temperature
Catalyst
Reversible reaction
REACTIONS
Synthesis Reaction
or Combination Reaction

Two or more simple substances react
to form a more complicated one
A + B  AB
Fe + S  FeS
Combination(synthesis) Reactions
We can predict the products of ionic compounds
by thinking about the charge!
Al (s) +
O2 (g) 
Al2O3
Cu (s) +
S(s)

CuS
Are there 2 possible products to these reactions?
How would we “say” these equations?
Decomposition Reaction

A decomposition reaction is the
opposite of a composition reaction a complex molecule breaks down to
make simpler ones.
AB  A + B
2 H 2O  2 H 2 + O2
Decomposition Reactions
Harder to predict the products…always
remember your diatomics.
Water is often a product!
HgO(s)

Hg
+
O2
NH4NO3

H2O
+
N2
Decomposition Reactions
HgO(s)
2HgO(s)


2Hg(l)
+
O2 (g)
NH4NO3
NH4NO3


N 2O
+
2H2O
The only way to really know is to do the
reaction!!
Single Replacement

This is when one element trades places
with another element in a compound.
A + BC  AC + B
Mg + 2H2O  Mg(OH)2 + H2
Single Replacement Reactions
Easy to predict the products. Look at the ions…
remember that a cation has to bond to an anion!!
Don’t forget about diatomics!
Zn(s) +
H2SO4(aq) 
Na(s) +
H2O 
Single Replacement Reactions
Zn(s) +
Zn(s) +
H2SO4(aq) 
H2SO4(aq)  ZnSO4(aq)
Na(s) +
Na(s) +
2Na(s)+
H 2O 
H+OH-(l) 
2H+OH-(l)  2NaOH + H2(g)
+ H2(g)
Single Replacement Reactions
Reactivity of a metal makes a
difference!
If a metal is more reactive than the
metal it is displacing a rxn will occur.
If the metal is less reactive than the
metal it is displacing, a rxn will not
occur.
Metal Reactivity
Increases down a group
Decreases across a period
Brainiacs-- Metal Reactivity
Reactivity in Single Displacement
Cs
Na
+
+
KMnO4  CsMnO4 + K
Will this occur??
KMnO4  NaMnO4 + K
Will this occur?
Double Replacement Reaction

This is when the anions and cations
of two different molecules switch
places, forming two entirely different
compounds
AB + CD  AD + CB
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
Generally take place between two ionic compounds in
aqueous solution
Generally 3 things happen:
1.
A precipitate (solid) occurs
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
2.
One product is a gas that bubbles
out of the mixture
2NaCN(aq) + H2SO4  2HCN(g) + Na2
SO4(aq)
Double Replacement Reactions
3.
One product is a molecule while the
other products are ions
Ca(OH)2(aq) + 2HCl(aq)  Ca+2 + Cl- + 2 H2O(l)
Combustion Reactions

A combustion reaction is when oxygen
combines with another compound or
element producing energy.
When hydrocarbons (C?H?) combust,
water, carbon dioxide and energy are
produced.
C10H8 + 12 O2  10 CO2 + 4 H2O + Energy

Combustion of Naphthalene
Combustion Reactions
Combustion of propane:
C3H8 +
O2

Combustion of methane:
CH4 +
O2

Combustion of butene (this one is tricky!)
C4H6 +
O2

Conservation of Mass
Law of Conservation of Mass
 In any physical or chemical reaction,
mass is neither created nor destroyed; it
is conserved!
Reactants
Products
Same number of atoms on both sides!
Balancing Equations
In every balanced equation
each side of the equation
has the same number of atoms
of each element
Balance this equation…
NaNO3 + CrCl3  NaCl + Cr(NO3)3
How would you “write” it?
Parts of a Reaction

Subscripts – tells how many atoms of each
element you have NH3 (one nitrogen, three
hydrogen)- DON’T mess with these!!

Coefficients – small whole number that
appears in front of a chemical formula in an
equation – you get to “mess” with these.
2NH3 (Two molecules of ammonia or two
moles of ammonia)

 the arrow means yields or reacts to produce
REACTANTS
PRODUCTS
You have to get the same number of
elements on each side of the reaction
The Rules
1.
2.
3.
4.
Never touch subscripts when balancing
equations, you will change the substance
Include all sources of the element
CH3CHOOH + NaOH
Polyatomic ions that appear intact on both
sides of the equation, can be balanced as a
group (PO4)
Coefficients in your balanced equation
contain the lowest possible ratio.
Balancing!
Aluminum + Oxygen  Aluminum Oxide
Al + O2  Al2O3
Until you get good at this, it is helpful
to write the number of atoms of each element on
both sides of the equation. It helps you to
keep track of the atoms.
Balancing!
Ethene + Oxygen  Carbon Dioxide + water
C2H4 + O2  CO2 + H2O
Balancing!
Hydrogen gas + nitrogen gas 
ammonia
Remember your diatomic molecules!!!
H2 + N2  NH3
Try this one!
NaNO3 + CrCl3  NaCl + Cr(NO3)3
Warm UpBalance the following equations:
C 3H 6 +
O2 
CO2 + H2O
C7H14 +
O2 
CO2 + H2O
What is a flame video- Science Friday
http://www.sciencefriday.com/video/06/08/
2012/what-is-a-flame.html
Recap: 5 Types of Reactions
Combination
2. Decomposition
3. Single Replacement
4. Double Replacement
5. Combustion
1.
Let’s talk about what you should
take next year…
Predict the products, balance and classify
the following reactions.
Li + MgCl2 
C6H12 + O2 
Ca(NO3)2 + NaOH 
Work on the predicting products
WS
Finish it as homework
The analysis articles are on the website…
will be due on test day. You can turn
it in
anytime between now and then.
Warm Up
Do the first 2 problems on the Balancing
Word Equations WS…..do both front and
back!!
What do the equations mean?
The coefficients indicate the number of
moles of the reactants necessary… to
form a certain mole of the product.
Mole to Mole Ratio
3K + AlCl3  Al + 3KCl
Word Equation WS
Don’t worry too much about the evidence!
Look for changes in state.
Types of Reaction Lab
1.
Divide your paper in half. Label each box, write
the type of reaction, the reactants and predict the
products for the following reactions (form
hypothesis).
a. Synthesis: Mg + O2
b. Decomposistion CaCO3
c. Single Replacement Zn + HCl
d. Double Replacement PbNO3 + KI
In each box…
Collect whatever data is asked for on
the lab instruction sheet.
2. Draw a picture of the set up.
3. Write observations… evidence that a
chemical change occurred.
4. Is the reaction endothermic or
exothermic?
1.
Warm Up QuizPredict the products, balance and classify the following reactions.
1. K + AlCl3 
2. Ca3(PO4)2 + Ba(OH)2 
3. O2 + C4H10 
Classify the type of reaction for each
of the above equations.
Let’s Grade it!
1. K + AlCl3 
2. Ca3(PO4)2 + Ba(OH)2 
3. O2 + C4H10 
Debrief Types of Rxns Lab
Types of Reaction Lab
Synthesis: Mg + O2 
Did the mass of the system change after the reaction took
place?
Did you detect the presence of ammonia gas?
Endothermic or exothermic?
Types of Reaction Lab
Decomposition CaCO3 
What evidence indicates a chemical reaction.
How do you know that carbon dioxide was formed?
Endothermic or exothermic?
Types of Reaction Lab
Single Replacement
Zn + HCl 
What evidence did you see?
What was in the little tube– how do you know?
Endothermic or exothermic?
Types of Reaction Lab
Double Replacement
PbNO3 + KI 
What evidence did you see?
Endothermic or exothermic?
Last thing…
Revisit your hypothesis… rewrite the
correct balanced equation.
Let’s look at the predicting WS
Questions on the Word Equations
WS?
Will a reaction occur???
Let’s look at the Activity Series and see.