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Chemical Reactions
Unit 7 Part 1
Chemical Equations and Reactions
 Chemical equations are used to show chemical reactions.
 Indicators of a Chemical Reaction Include:
 Change in color (unexpected)
 Production/release of a gas (bubbles)
 Change in temperature
 Exothermic
 Endothermic
 Formation of a precipitate (solid)
Law of Conservation of Mass
 Matter cannot be created nor destroyed, it can only change
forms.
 Chemical equations must ALWAYS be balanced to obey the
law of conservation of mass.
 Mass has to be the same on both sides of the reaction.
 The number of atoms has to be the same for the products
and reactants.
 What you start with, you must end with
Components of a Chemical Equation
 Reactants
 Listed on the LEFT side of the equation.
 Starting substances (ingredients)
 Products
 Listed on the RIGHT side of the equation.
 Ending substances (produced substance)
 Arrow  “Yields”
 States of Matter
 Solid (s)
 Liquid (l)
 Gas (g)
 Aqueous (aq)
 Coefficients
 Whole number that proceeds the chemical substance (number of moles of the
substance)
Steps to Follow to Balance Equations
1.
Determine the number of atoms for each element.
2.
Pick an element that is not equal on both sides of the
equation.
3.
Add a coefficient in front of the formula with that
element and adjust your counts.
4.
Continue adding coefficients to get the same number
of atoms of each element on each side.
**Note: LEAVE THE SUBSCRIPTS ALONE! (you cannot
change the chemical formula to balance atoms)
Coefficients
 Coefficients go in front of a compound
4H2O
-All atoms in a compound are multiplied by the coefficient
Number of atoms:
HydrogenOxygen-
Practice With Coefficients
*List the amount of each atom in the 4 substances below:
4CH4
3NH3
3Ni(NO3)2
4Ca3(PO4)2
Class Examples - Model
 See hand out for chemical formulas.
Balancing Word Equations: (See additional steps on next slide)
 Potassium chlorate  potassium chloride + oxygen
 When solid copper reacts with aqueous silver nitrate, the
products are aqueous copper (II) nitrate and silver metal.
 Nitrogen and oxygen combine to form dinitrogen pentaoxide
Steps to Write Equations
1. When writing formulas don’t forget to look up
charges if the compound is ionic!!!
2. Diatomic Molecules: Always travel in pairs
1. H.O.F.Br.I.N.Cl. (Dr. HOFINBrCl)
2. These elements need a subscript 2 after them if
they are by themselves!
3. Once the equation is written, then balance the
equation by adding coefficients.
Check for Understanding
Balance the following Chemical Equations:
 CH4 + O2  CO2 + H2O
 Na2O2 + H2SO4  Na2SO4 + H2O2
 N2 + H2 NH3
 When solid copper reacts with aqueous silver nitrate,
the products are aqueous copper (II) nitrate and silver
metal.
Steps to Follow to Balance Equations
1.
Determine the number of atoms for each element.
2.
Pick an element that is not equal on both sides of the
equation.
3.
Add a coefficient in front of the formula with that
element and adjust your counts.
4.
Continue adding coefficients to get the same number
of atoms of each element on each side.
**Note: LEAVE THE SUBSCRIPTS ALONE! (you cannot
change the chemical formula to balance atoms)
Steps to Write Equations
1. When writing formulas don’t forget to look up
charges if the compound is ionic!!!
2. Diatomic Molecules: Always travel in pairs
1. H.O.F.Br.I.N.Cl. (Dr. HOFINBrCl)
2. These elements need a subscript 2 after them if
they are by themselves!
3. Once the equation is written, then balance the
equation by adding coefficients.
Types of Chemical
Reactions
Unit 7 Part 2
Types of Chemical Reactions – WHY?
 Recognizing patterns allows us to predict future
behavior.
 Weather experts use patterns to predict dangerous
storms so people can get their families to safety.
 Political analysts use patterns to predict election
outcomes.
 Similarly, chemists classify chemical equations
according to their patterns to help predict products of
unknown but similar chemical reactions.
Synthesis Reaction
Synthesis Reaction: A reaction in which two or
more substances combine to form ONE new
compound.
A + B
AB
Examples of Synthesis Rxn
A +B
Water:
H2 + O2
Table Salt: Na + Cl2
AB
H2O
NaCl
Given the following reactants, predict the products.
S8 + O2
Synthesis: 2Mg + O2 → 2MgO
Decomposition Reactions
Decomposition Reaction: A reaction in which a
single compound breaks down to form two or
more simpler substances.
AB
A + B
Examples of Decomposition Rxn
Digestion is a series of decomposition reactions that break
down food for fuel for your body.
The production of gasoline is done by “cracking” crude oil
where you break down carbon and hydrogen molecules.
Electrolysis of water:
H2O
H2 + O2
Decomposition: C12H22O11 → 12C + 11H2O
Single Displacement Reaction
Single Displacement Reaction: A reaction in which one
element takes the place of another element in a
compound.
* A more reactive element will take the place of a less
reactive element. (see page 286 Table 3)
AX + B
BX + A
Examples of Single Displacement
Zn + HCl
ZnCl2 + H2
Q: In the example above, which element is more reactive?
CuCl2 + Al
Q: In the above example, predict the products.
Single Replacement: Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
Double Displacement Reaction
Double Displacement Reaction: A reaction where there is an
apparent exchange of atoms or ions between two
compounds.
AX + BY
AY + BX
Indicators of a double displacement reaction:
 Formation of a Precipitate (solid)
 Formation of a Gas (bubbles)
 Formation of Water
Example of Double Displacement
The yellow lines on the roads are made from a double
displacement reaction.
Pb(NO3)2 + K2CrO4
PbCrO4 + KNO3
Double Replacement: 3CuCl2 + 2Na3PO4 → Cu3(PO4)2 + 6NaCl
Combustion Reactions
Combustion Reactions: A reaction where an organic
molecule is combined with oxygen.
CxHy + O2
 Oxygen (O2) is a reactant.
 CO2 and H2O are produced
CO2 + H2O
Uses for Combustion
Combustion reactions are used in your home everyday in stoves,
water heaters, and furnaces.
Example of Combustion Reaction:
2CH4 + 4O2
2CO2 + 4H2O
Combustion: CH4 + 2O2 → CO2 + 2H2O
Practice
(in your notes)
 Balance and Classify the following chemical reactions:
 __Mg + ___HCl
 __C4H8 + ___ O2
 ___Ca(OH) 2 + ___H2 SO4
 ___N2 + ___O2
____MgCl2 + ____H2
____CO2 + ____ H2O
____CaSO4 + ___H2O
____N2O5
Types of Reactions DEMO Activity
 LAB Pictures
 Feel free to share –
 Email: [email protected]
 Keys to success Be sure your hand is VERY soapy!!
 Keep your hand flat
 Keep all your fingers together and “tuck your thumb in”
 Do NOT move your hand once it is on fire.
 Do not forget to SMILE for your picture! 
Chemical Equations/Reactions Exam
Acid-Base Reactions
Acid/Base Rxn: The reactants will include an acid
combining with a base. The products will include
water and a salt.
HX + B(OH)
H2O + BX
Acid-Base Reactions
 The Bronsted-Lowry Definitions
 Acid is a proton donor.
 Base is a proton acceptor.
 An acid-base reaction is often called a neutralization
reaction.
Examples of Acid/Base Reaction
HCl + Ca(OH)2
H2O + CaCl2
HCN + K(OH)
H2O + KCN
Chemistry 1
(Chapter 13)
Ions in Aqueous
Solutions and
Colligative Properties
Questions From Readings
 Explain what
happens when
an ionic
substance is
dissolved in
water.
(examples to
strengthen
response)
Dissociation reactions …
 AgNO3 
 KBr 
 BaSO4
Questions from Reading
 What is a
precipitation
reaction? How
can you
determine if the
reaction occurs?
Precipitate Reactions (ppt)

Precipitate: An insoluble solid
compound is formed during a reaction.

Anions are exchanged between two cations.


To be a ppt. rxn, both must occur:



(This is a double displacement reaction)
1. Both reactants must be aqueous (aq)
2. At least one product must be a solid (s)
You MUST include phase labels with your
equation. (See solubility table)
Predicting Solubility of Compounds

Use a solubility table to determine if a substance is
going to be soluble (aqueous) or insoluble (solid) in
water
a) Hg2Cl2
b) KI
c) lead (II) nitrate
Practice Solubility
5 Minutes!
Rules for ppt. reactions
1. Write a balanced chemical equation.
2. Use the solubility table to place phase labels
to each formula.
3. If one of the products is a solid and the
reactants are aqueous the reaction is
classified as a precipitate reaction.
4. If all of the products are (aq) then the reaction
is NOT a ppt rxn and is classified as double
displacement.
Q: For each of the following decide if a
ppt. will occur.
A) Aqueous solutions of sodium chloride
and iron (II) nitrate are mixed.
B) Aqueous solutions of aluminum sulfate
and sodium hydroxide are mixed.
Check for Understanding
For the following reactions, predict the identity of the
precipitate formed. Write the correct formula of the precipitate
on the space. If no precipitate is likely, write No Reaction.
 BaCl2 and K2SO4
______________________
 CuCl2 and AgNO3 ______________________
 (NH4)3PO4 and CaS______________________
 KCl and Ca(NO3)2 ______________________
Ionic Equations
 Molecular Equation: Chemical equation in which the
reactants and products are written as if they were
molecular substances, even though they may exist in
solutions as ions.
 Must include phase labels (s, l, g, aq)
 This provides you with the big picture
Example:
Al2(SO4)3(aq)+ 6NaOH(aq) ----- 2Al(OH)3(s)+ 3Na2SO4(aq)
The next 2 types of equations are only
completed for precipitate reactions!!!
 Complete ionic equation: Shows all the particles in the
solution as they realistically exist.
 Break apart the aqueous substances into their
ions.
 Do NOT break apart s, l, or g!!
 When writing a complete ionic equation include
the Amount, Symbol and CHARGE!
Example of a Complete Ionic Equation
Molecular Equation:
Al2(SO4)3(aq)+ 6NaOH(aq)--- 2Al(OH)3(s)+3Na2SO4(aq)
Complete Ionic Equation: Amount, Symbol, Charge
Last step for precipitate reaction:
 Net ionic equation: Ionic equations that
include only the particles that participate in
the reaction.
 This tells us what substances actually
formed something new in the reaction.
 Cross out the spectator ions
Writing Net Ionic Equation
Molecular Equation:
Al2(SO4)3(aq)+ 6NaOH(aq)--- 2Al(OH)3(s)+3Na2SO4(aq)
Complete Ionic Equation: Amount, Symbol, Charge
2Al+3 + 3SO4-2 + 6Na+1 + 6OH-1 ---- 2Al(OH)3 + 6Na+1 + 3SO4-2
Net Ionic Equation:
What formed during the reaction?
One more example of a precipitate
reaction
Calcium hydroxide reacts with sodium carbonate to
produce calcium carbonate and sodium hydroxide
Molecular Equation:
Complete Ionic Equation:
Net Ionic Equation:
Check for Understanding
 Why are complete ionic equations more informative than
molecular equations for reactions of ions in aqueous
solutions?
 What is the difference between a complete/total ionic
equation and a net ionic equation?
 Why are spectator ions left out of the net ionic equation?
 What substance is designated with an (s) in the net ionic
equation? What state designation do the other substances
have?
 Why is it necessary to balance the molecular equation before
writing the total and net ionic equation?
Check for Understanding
 Explain the difference between ionization and
dissociation.
 What determines how much a solute ionizes in solution?
 Explain how to tell the difference between a strong
electrolyte and a weak electrolyte.
Check for Understanding
 Explain the difference between ionization and dissociation.
 Ionization occurs when ions are formed from the solute particles due to the action of
the solvent.
 Dissociation occurs when an ionic compound dissolves into ion.
 Difference is ionization’s ions are formed from molecular compounds, not ionic
compounds.
 What determines how much a solute ionizes in solution?

The strength of the solute molecules

The strength of attraction between solute and solvent
 Explain how to tell the difference between a strong
electrolyte and a weak electrolyte.

The degree of ionization or dissociation is what determines strength of electrolyte, not the amount of solute
dissolved.
Oxidation Reduction (REDOX) Reactions
 Reactions in which one or more electrons are transferred
(redox reactions)
 Example:
H2(g) + Cl2(g)
2HCl(g)
Electrons are transferred from the hydrogen to the chlorine.
 Recall Rules for Assigning Oxidation States
 Remember: The sum of the oxidation states in a neutral
compound must equal zero.
Oxidation States
 Assign oxidation states to each of the atoms in the following
compounds:
Hint: Check that oxidation states sum up to the charge on the compound/ion.
 CaF2
 C2H6
 H2O
 ICl5
 KMnO4
 SO42-
Practice- Oxidation States
Fe2O3 + 2Al
Al2O3 + 2Fe
THE IRON GAINED ELECTRONS. IT HAS BEEN REDUCED.
THE ALUMINUM LOST ELECTRONS. IT HAS BEEN OXIDIZED.
OIL – Oxidation Involves Loss (of electrons)
RIG- Reduction Involves Gain (of electrons)
OIL RIG Practice
 For each reaction, identify the atoms that undergo reduction or
oxidation (and charges). Also, list the oxidizing and reducing
agents.
2H2(g) + O2(g)
2H2O(g)
Zn(s) + Cu2+(aq)
Zn2+(aq) + Cu(s)
2AgCl(s) + H2(g)
2H+(aq) + 2Ag(s) + 2Cl-(aq)