1. Chemical Equations & Reactions
Chemical Reaction - Study Questions
1. What is a chemical reaction?
2. What is evidence a reaction has occurred?
3. What is a chemical equation?
4. Define reactants.
5. Define products.
6. Define catalyst.
7. What information is found in an equation?
8. What symbols are used to represent the states of matter?
9. What is the meaning of “aq”?
10. How do you indicate a catalyst is being used in a reaction?
11. What is activation energy?
12. What the three things does conservation of matter require of chemical equations?
13. What is the procedure for balancing a chemical equation?
14. Balance the equation for the reaction of magnesium chloride and silver nitrate to form magnesium nitrate and silver chloride.
15. What is a synthesis reaction?
16. How is a combustion reaction related to a synthesis reaction?
17. What type of reaction is an explosion?
18. Compare decomposition and dissociation.
19. What determines whether one metal will replace another in a single displacement reaction?
20. What is the general form of a double displacement reaction?
21. What type of reaction is each of these?
2Na(s) + Cl2(g)  2NaCl(s)
PCl5(s)  PCl3(s) + Cl2(g)
2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s)
C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O(l)
BaCl2(aq) + H2SO4(aq)  2HCl(aq) + BaSO4(s)
22. What is the oxidation number of an element?
23. What is the oxidation number of the fluorine ion?
24. What is the sum of the oxidation numbers in a compound?
31. Can a redox reaction form a molecule? Explain your answer.
Chemistry A

2. Chemical Reactions You should be able to Classify reactions by type.
Write a balanced molecular equation, complete ionic equation,
and a net ionic equation.
Predict products of reactions given the chemical names of the
reactants.
What you should learn:
In chemical change atoms are rearranged but no atoms are created and none are destroyed
Chemical equations are symbolic representations of what is happening at the molecular level and are used to communicate the conditions under which a reaction proceeds, the products and amount of energy that results, and allow for predictions to be made.
More Specifically...:
Classify those equations that come under the heading of synthesis, decomposition, single replacement, double replacement, neutralization, oxidation/ reduction and combustion
Identify and name acids and bases
Use principle of conservation of mass to balance a reaction
From a written description of a reaction write a balanced reaction using correct state symbols
Show that the conservation of mass is true for a balanced reaction
Predict the products of chemical reactions (including state symbols) when given the reactants.
Use an activity series to predict the spontaneity of reactions.
Use solubility rules to predict the formation of a precipitate
Define oxidation and reduction, and identify any species undergoing oxidation or reduction, and identify the oxidizing and reducing agents
Write half reactions for single replacement reactions (monoatomic ions only)
Fast Track to a 5 (page 61)
To know how to calculate the molecular mass of a covalent compound and the formula mass of an ionic compound
To be able to use the concepts of the mole and molar mass to calculate the number of atoms, molecules, or formula units in a sample of a substance
To be able to determine the empirical formula of a compound from its composition by mass
To know how to derive the molecular formula of a compound from its empirical formula
To be able to describe a chemical reaction
To know how to calculate the quantities of compounds produced or consumed in a chemical reaction
To identify fundamental types of chemical reactions
To begin to predict the types of chemical reactions that substances undergo

3. Organize Your Thoughts
Chemical
reactions
Chemical
equations
Chemical
equations
To identify the reactants and products in a chemical equation.
To balance a chemical equation with coefficients.
To identify synthesis (combination), decomposition, and combustion reactions.
To identify single-replacement reactions.
To identify double-replacement reactions.
To predict the products of a reaction.
Synthesis
Decomposition
Single replacement
Double replacement
Combustion
Balancing equations
Predicting products
from reactants
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

4. Chemical Reaction
A process in which at least one new substance is produced as a result of chemical change.

5. A Chemical Reaction
Reactants Products

6. Describing a Chemical Reaction
Indications of a Chemical Reaction
Evolution of heat, light, and/or sound
Production of a gas
Formation of a precipitate
Color change
Objective:
To state four observations that are evidence for a chemical reaction.
Photo of precipitate:

7. Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
release
input
change in color
change in odor
production of new
gases or vapor
input or release
of energy
difficult to reverse

8. Writing a Chemical Equation
Chemical symbols give a “before-and-after” picture of a chemical reaction
Reactants Products
MgO C CO Mg
magnesium oxide to form carbon monoxide
reacts with carbon and magnesium

9. Learning Check E3
12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza.
How would you write the recipe as an equation?

10. Solution E3
Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza
12 oz dough + 4 oz mshrm
+ 12 pep + 8 oz chse pizza
+ 5 oz tom sauce

11. Chemical Equations Depict the kind of reactants and products
aluminum oxide
Depict the kind of reactants and products
and their relative amounts in a reaction.
reactants
product
4 Al(s) O2(g) Al2O3(s)
A chemical equation is an expression that gives the identities and quantities of the substances in a chemical reaction
Chemical formulas and other symbols are used to indicate the starting material(s) or reactant(s), which are written on the left side of the equation, and the final compound(s) or product(s), which are written on the right side. An arrow, read as yields or reacts to form, points from the reactants to the products.
Abbreviations are added in parentheses as subscripts to indicate the physical state of each species:—(s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution.
A balanced chemical equation is when both the numbers of each type of atom and the total charge are the same on both sides. A chemical reaction represents a change in the distribution of atoms but not in the number of atoms.
The letters (s), (g), and (l) are the
physical states of compounds.
The numbers in the front are called
stoichiometric coefficients.

12. Chemical Equations 4 Al(s) + 3 O2(g) 2 Al2O3(s)
aluminum oxide
sandpaper
4 Al(s) O2(g) Al2O3(s)
4 g Al g O2 yield 2 g Al2O3
This equation means:
4 Al atoms O2 molecules yield 2 molecules of Al2O3 or
4 Al moles O2 moles yield 2 moles of Al2O3
4 mol
3 mol
2 mol
108 g g = g

13. Chemical Equations Because the same atoms are present
in a reaction at the beginning (reactants)
and at the end (products), the amount
of matter in a system does not change.
The Law of Conservation of Matter
Law of Conservation of Matter means that nothing is “lost” or “stolen”. In the real world retail theft costs business lots (much of the theft is actually employee theft)!
20%
100%
Chemical
Factory
100%
80%
Kotz web

14. Chemical Equations
Because of the principle of the conservation of matter,
An equation must be balanced.
It must have the same number of atoms
of the same kind on both sides.
Lavoisier, 1788

15. Characteristics of Chemical Equations
The equation must represent known facts.
The equation must contain the correct formulas for the reactants and products.
The law of conservation of mass must be satisfied.

16. Chemical Equations
Reactants – the substances that exist before a chemical change (or reaction) takes place.
Products – the new substance(s) that are formed during the chemical changes.
CHEMICAL EQUATION indicates the reactants and products of a reaction.
Objectives:
To identify seven elements that occur naturally as diatomic molecules, H2, N2, O2, F2, Cl2, Br2, I2. [HOBrFINCL twins or BrINClHOF brothers]
To write a chemical equation from the description of a chemical reaction.
REACTANTS  PRODUCTS

17. Word Equations
A WORD EQUATION describes chemical change using the names of the reactants and products.
Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.
methane oxygen
carbon dioxide water
Reactant
Product
CH4 + 2 O2
CO2 + 2
H2O

18. Unbalanced and Balanced EquationsH Cl Cl H Cl Cl H H
H2 + Cl2  HCl
(unbalanced)
H2 + Cl2  2 HCl
(balanced)
reactants products H Cl
reactants products H Cl 2 1 2 2 2 1 2 2

19. Visualizing a Chemical Reaction2
Na Cl NaCl 2
___ mole Na 10 10
___ mole Cl2 5 5
___ mole NaCl 10 10 ?

20. Visualizing a Chemical Reaction2
Na Cl NaCl 2

21. Meaning of Chemical Formula
Symbol Meaning Composition
H2O One molecule
of water:
Two H atoms and one O atom
2 H2O Two molecules
of water:
Four H atoms and two O atoms
H2O2 One molecule
of hydrogen
peroxide:
Two H atoms and two O atoms

22. Balancing Chemical Equations
Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product
What is the relationship between conservation of mass and
the fact that a balanced equation will always have the same
number of atoms of each element on both sides of an equation?
Objective:
To write balanced chemical equations by inspection.
Balanced chemical equation
– Provides qualitative information about the identities and physical states of the reactants and products
– Provides quantitative information because it tells the relative amounts of reactants and products consumed or produced in the reaction
– The number of atoms, molecules, or formula units of a reactant or product in a balanced chemical equation is the coefficient of that species
– Mole ratio of two substances in a chemical reaction is the ratio of their coefficients in the balanced chemical equation
Determine whether the following equation is balanced.
2 Na + H2O  2 NaOH + H2
2 Na H2O  2 NaOH + H2

23. Balancing Chemical Equations
Write a word equation for the reaction.
Write the correct formulas for all reactants and products.
Determine the coefficients that make the equation balance.

24. Balancing Chemical Equations
Other examples
NO(g) + O2(g)  NO2(g)
is it balanced?
Is this balanced?
NO(g) + O(g)  NO2(g)
Is this OK?
Is this balanced?
NO(g) + ½ O2(g)  NO2(g)
Is this OK?

25. Balancing Chemical Equations
An important point to remember
2 NO(g) + O2(g)  2NO2(g)
The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation.
It is a “multiplier” for every atom in the molecule.
The subscript 2 in O2 (g) and NO2(g) refers to the number
of atoms of this type that are present in each molecules
(or ionic compound).

26. Write a balanced equation for the reaction between chlorine
and sodium bromide to produce bromine and sodium chloride.
1) Write a word equation for the reaction.
chlorine sodium bromide  bromine + sodium chloride
2) Write the correct formulas for all reactants and products.
Cl NaBr  Br NaCl
3) Determine the coefficients that make the equation balance.
Cl NaBr  Br NaCl

27. Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate.
1) Write a word equation for the reaction. ? ?
aluminum sulfate + calcium chloride  calcium sulfate
+ aluminum chloride
2) Write the correct formulas for all reactants and products.
Al2(SO4) CaCl  CaSO AlCl3
3) Determine the coefficients that make the equation balance.
Al2(SO4) CaCl  CaSO AlCl3

28. CH4 + 2 O2  CO2 + 2 H2O Reactants Products 1 C atom 1 C atom
4 H atoms H atoms
4 O atoms O atoms

29. Reactants  Products + C(s) + O2(g) CO2(g) + H2(g) + O2(g) H2O (l) 2 2
carbon oxygen carbon dioxide
Reactants Product
1 carbon atom carbon atom
2 oxygen atoms oxygen atoms
catalyst – speeds up reaction + Pt
H2(g) O2(g) H2O (l)
hydrogen oxygen water 2 Pt 2
Reactants Product
4 hydrogen atoms hydrogen atoms
2 oxygen atoms oxygen atoms
Reactants Product
2 hydrogen atoms hydrogen atoms
2 oxygen atoms oxygen atoms
Reactants Product
2 hydrogen atoms hydrogen atoms
2 oxygen atoms oxygen atoms Un
balanced

30. Reactants  Products
catalyst – speeds up reaction 2 2
Unbalanced

31. Showing Phases in Chemical Equations
H2O(s) H2O(l) H2O(g)
Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s)
Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l)
Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g)

32. Additional Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reaction
A reactant or product in the solid state;
also used to indicate a precipitate
Alternative to (s), but used only to indicate a precipitate
A reactant or product in the liquid state
A reactant or product in an aqueous solution
(dissolved in water)
A reactant or product in the gaseous state
(s)
(l)
(aq)
(g)

33. Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a gaseous product
Reactants are heated
Pressure at which reaction is carried out, in this case 2 atm
Pressure at which reaction is carried out exceeds normal
atmospheric pressure
Temperature at which reaction is carried out, in this case 0 oC
Formula of catalyst, in this case manganese (IV) oxide,
used to alter the rate of the reaction D
2 atm
pressure
0 oC
MnO2

34. Types of Chemical Reactions
Synthesis (Combination) reaction
A B  AB
Decomposition reaction
AB  A + B
ASingle-replacement reaction
A BC  AC + B
element
compound
compound
element
BDouble-replacement reaction
AB CD  AD + CB
compound
compound
compound
compound
Neutralization reaction
HX BOH  BX + HOH
Objective:
To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization.
acid
base
salt
water
CH O2  CO2 + H2O
Combustion reaction (of a hydrocarbon)
Polymerization
Polymer = monomer + monomer + …
Ause activity series to predict
Bdriving force…water, gas, or precipitate

35. Types of Chemical Reactions
Synthesis (Combination) reaction
A B  AB
Decomposition reaction
AB  A + B
ASingle-replacement reaction
A BC  AC + B
BDouble-replacement reaction
AB CD  AD + CB
Neutralization reaction
HX BOH  BX + HOH
CH O2  CO2 + H2O
Objective:
To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization.
Combustion reaction (of a hydrocarbon)
Polymerization
Polymer = monomer + monomer + …
Ause activity series to predict
Bdriving force…water, gas, or precipitate

36. Synthesis Reaction Direct combination reaction (Synthesis)
2 Na Cl  NaCl Na Na Cl Cl  Cl Cl Na Na
General form: A B  AB
element or element or compound
compound compound

37. Synthesis Reaction Direct combination reaction (Synthesis)
2 Na Cl  NaCl Na Cl
Na+
Cl - Cl
Cl -
Na+ Na
General form: A B  AB
element or element or compound
compound compound

38. Decomposition Reaction
2 H2O +
2 H2 O2 H H O O H + H O O H
General form: AB A + B
compound
two or more elements
or compounds

39. Single and Double Replacement Reactions
Single-replacement reaction
Mg CuSO4  MgSO Cu
General form:
A BC  AC B
Double-replacement reaction
CaCO HCl  CaCl H2CO3
General form:
AB CD  AD CB

40. Double Replacement Reaction
K2CO3 (aq)
Potassium carbonate +
BaCl2 (aq)
Barium chloride
2 KCl (aq)
Potassium chloride +
BaCO3 (s)
Barium carbonate

41. Synthesis Reactions Photosynthesis 6 CO2 + H2O C6H12O6 + O2 6 6
Formation of water 2
H O H2O 2
Formation of salt
A photomicrograph of common table salt © Carl J. Bowser, Department of Geology and Geophysics, University of Wisconsin, Madison 2
Na Cl NaCl 2
General Form
A B C

42. Decomposition Reactions
Hydrogen Peroxide 2
H2O H2O O2 2
Electrolysis of water
H2O H O2
electricity 2 2
Nitrogen triiodide 2
NI N I2 3
General Form
AB A B