Chemical Reactions POPS Chemistry Unit 4 – Student Notes
Chemical Reactions
 _________________________________________________________________________________
 Reactants = starting substances
 ________________________________________________________________________________Arrow
always points to the products
_______________________________________________________________________________
Example of Chemical Reactions
 Zn + 2 HCl → ZnCl2 + H2
 What are the reactants?
 ________________________________________________________________________________What
are the products?
________________________________________________________________________________
How do you know when a chemical reaction takes place?
 _____________________________________
 _____________________________________
Chemical Reactions
A chemical change: any change in which a new substance is formed.
Evidence of a Chemical Change:
 Release of energy as heat
 _____________________________________
 Change in color
 _____________________________________
 Change in odor…
Meanings of some symbols
Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type
of reaction it illustrates. Use the code below to classify each reaction.
S = Synthesis D = Decomposition
____ P + O2 → P4O10
____ HgO → Hg +
O2
____ Cl2 + NaBr → NaCl + Br2
SR = Single Replacement DR = Double Replacement
____ Mg + O2 → MgO
____ Al2O3 → Al + O2
____ H2 + N2 → NH3
____ HgO + Cl2 → HgCl + O2
____ C + H2 →
____ KClO3 →
____ S8 +
KCl +
O2
____ BaCl2 + Na2 SO4 →
F2 →
CH4
SF6
NaCl + BaSO4
What is a combustion
 A combustion reaction is a type of reaction in which a combustible material combines and generates
heat (exothermic reaction).
 The reactants are almost always a hydrocarbon and oxygen and the products are almost always carbon
dioxide and water
 General Form of a Combustion Reaction
 hydrocarbon + oxygen → carbon dioxide + water
 Example
C10H8 + 12 O2 → 10 CO2 + 4 H2O
You Try
1.
methane (CH4)
2.
ethane (C2H6)
3.
propane (C3H8)
4.
butane (C4H10)
+
+

oxygen
oxygen

+ oxygen 
+
oxygen

Law of conservation of Matter
 _____________________________________
 This means that the number of atoms of each type must be the same in the products and the reactants.
 _____________________________________.
Balancing Equations
 Subscript: ____________________________________________________________________________
 Coefficient_____________________________________
Ex: 2H2 + O2  2H2O
Steps to Balancing an Equation
1. _________________________________________________________________________________
__________________________________________________________________________________.
2. Make a list below both the reactants and the products and list all of the atoms in each element in the
equation. Determine if the equation is balanced or not. If it is a balanced equation, it has the same
number of atoms of each element on both sides of the arrow. If the equation does not have the same
number of atoms of element on both sides of the arrow, then it is not balanced.
3. _________________________________________________________________________________
__________________________________________________________________________________
4. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list
the number of atoms of each element on each side.
5. It is often easiest to start balancing with an element that appears only once on each side of the arrow.
These elements must have the same coefficient. Next balance elements that appear only once on each
side but have different numbers of atoms. Finally balance elements that are in two formulas in the same
side.
Example of how to balance an equation
Start with an equation.
Mg + O2  MgO
__________________________________________________________________________
Mg + O2  MgO
Mg
O
Mg
O
Then start balancing:
 [1] _________________________________________________________________
Mg + O2  MgO
Mg
O
1
2
1
1
 [2] _________________________________________________________________
Mg + O2 
2 MgO
1
2
Mg
O
2
2
And adjust totals
But the numbers still aren’t equal, so add another “BIG” number
2Mg + O2 
2MgO
2
2
2
2
Mg
O
And adjust totals again
NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS
______________________________________________________
Try to balance these equations using the same method:
[1] Na + Cl2  NaCl
[2] CH4 + O2  CO2 + H2O
[3] Li + HNO3  LiNO3 + H2
[4] Al + O2  Al2O3
Oxidation reactions are always accompanied by a reduction reaction
Oxidation
 _____________________________________
 iron rusting (iron + oxygen)
Reduction
 _____________________________________
 removing iron from iron ore ( iron II oxide)
Today
 OXIDATION means:
 _____________________________________


REDUCTION means:
_____________________________________


Memory Device :
_____________________________________
-
The substance that donates electrons in a redox reaction is the REDUCING AGENT
__________________________________________________________________
Oxidation is…
– the loss of electrons
– an increase in oxidation state
– ______________________________
– the loss of hydrogen
2 Mg + O2
2 MgO
notice the magnesium is losing electrons
Reduction is…
the gain of electrons
a decrease in oxidation state
__________________________________
the addition of hydrogen
MgO + H2
Mg + H2O
2+
notice the Mg in MgO is gaining electrons
Let’s Practice
)
2 Na + FeCl2  2 NaCl + Fe
2)
2 C2H2 + 5 O2  4 CO2 + 2 H2O
3)
2 PbS + 3 O2  2 SO2 + 2 PbO
Acid and bases reactions
What is an acid?
- An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means
"sharp" or "sour".
- _____________________________________
Properties of an Acid
 Tastes Sour
 _____________________________________
 Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin, and
paper
 _____________________________________
 Turns blue litmus paper red
Uses of Acids
 Acetic Acid = Vinegar
 Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch.
 _____________________________________.
 Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics.
 _____________________________________
What is a base?
 A base is a solution that has an excess of OH- ions.
 _____________________________________.
 _____________________________________
Properties of a Base
 Feel Slippery
 _____________________________________
 _____________________________________
 Can conduct electricity. (Think alkaline batteries.)
 Do not react with metals.
 _____________________________________.
Uses of Bases
 Bases give soaps, ammonia, and many other cleaning products some of their useful properties.
 The OH- ions interact strongly with certain substances, such as dirt and grease.
 _________________________________________________________________
 Your blood is a basic solution.







pH is a measure of how acidic or basic a solution is.
_____________________________________.
Acidic solutions have pH values below 7
A solution with a pH of 0 is very acidic.
_____________________________________
Pure water has a pH of 7.
_____________________________________
pH Scale
• ________________________________________________________________________
• For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not
twice as acidic as the second—it is ten times more acidic.
Acid – Base Reactions
 ______________________________________________________________________________
 An acid-base mixture is not as acidic or basic as the individual starting solutions.
Neutralization Reactions
 An acid base reaction often produces water and salt. The general form of a acid base reaction is
 _____________________________________
Example
HCl + NaOH
NaCl + H20



___________________________________________________
between an acid and a base.
Can you guess which acids and bases were the reactants?
Applications
Some Important Equations To Know
 Equation for Photosynthesis
 _____________________________________
 Equation for Cell Respiration
 _____________________________________
Chemical reactions happen when
 a car is started
 _____________________________________
 fertilizer is added to help plants grow
 _____________________________________
 electricity is produced from burning natural gas
 _____________________________________
Everything in our lives from materials to life involve chemistry
glass (SiO2)n
 metal alloys
 _____________________________________
 plastics and polymers
 _____________________________________
 foods
 _____________________________________
 living beings
 _____________________________________
Chemistry is Cool!