Unit 6 Notes Guide – Part 1 Name # Chemical Equations Block Chemistry

I. Reviewa. Chemical change

i. A change in a substance which results in the production of one or more new

substances

ii. A change which alters the chemical composition of a substance.

Ex: Formation of H2O from O2 and H2

iii. All chemical reactions are examples of chemical changes.

iv. Evidence for a chemical change:• Color change• pH change• Temperature change• Formation of a gas (bubbles)• Formation of a solid (precipitate)

b. Energy changes

i. Temperature changes indicate changes in energy.

ii. Endothermic – Energy is absorbed by the system The products have more kinetic energy than the reactants H is positive because heat had to be added

Heat is a “reactant”

iii. Exothermic – Energy is released by the system The reactants have more kinetic energy than the reactants H is negative because heat had to be subtracted Heat is a “product”

II. Chemical Reactionsa. Chemical Equation –

i. Represents ______________, ________________, and relative ______________ of reactants

and products within a chemical reaction

b. Chemical Formula -

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i. Represents the ____________ of __________ for each element that is in the molecule/compound

c. Molar Coefficient –

i. The ____________ in __________ of the chemical formula to represent the number of

__________ (____________) required to react or that the reaction produces

d. Reactant –

i. A substance that ____________ in a chemical reaction (________ side of arrow)

e. Product –

i. A substance ____________ in a chemical reaction (__________ side of arrow)

Symbols in Equations

Symbol Meaning

+

(sometimes , ⇋, or ⇄)

(s)

(l)

(g)

(aq)f. All chemical reactions include the chemical formulas and phases of each reactant and product

separated by a + sign, coefficients before each formula to indicate the number of each type of atom or molecule, and an arrow to indicate where the change occurs.

2 H2 (g)+ O2 (g) 2 H2O (l)Reactants Products

2 gaseous H2 molecules 2 liquid water molecules1 gaseous O2 molecule

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Practice:For each of the chemical equations below, identify the chemical formulas of the reactants and the products, state what phase each is in, and state the mole ratios of all the products and reactants. See the sample below.

Chemical EquationReactants Products

Formula Phase Formula Phase

2 H2 (g)+ O2 (g) 2 H2O (l)H2 Gas

H2O LiquidO2 Gas

Ca (s) + 2HCl (g) →

CaCl2 (s) + H2 (g)

2Ag (s) + S (g) → Ag2S (s)

Fe(OH)2 (s) → FeO (s) + H2O (l)

Mg (s) + 2AgNO3 (aq) →

Mg(NO3)2 (aq) + 2Ag (s)

3Ba(NO3)2 (aq) + 2Na3PO4 (aq) →

Ba3(PO4)2(s) + 6NaNO3 (aq)

III. Writing Chemical Equationsa. Chemical reactions can be written as sentences that can be translated into chemical

equations using key words b. Look for the words “to form” or “combine” or “to yield” or “to produce”

i. This is where the arrow occursii. Every chemical formula before these words are reactants and after are products

Symbol Key Word

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To form / combine / to yield / to produce+ And / reacts with(s) Solid / powder / metal(l) Liquid(g) Gas / vapor(aq) Solution / dissolved

Example:Aluminum metal reacts with silver sulfate solution to form aluminum sulfate solution and silver metal.

Practice:Write the chemical equations for the following reactions:

1. Methane (CH4) gas reacts with oxygen gas to form carbon dioxide gas and water vapor.

2. Lead (II) nitrate, Pb(NO3)2, solution reacts with iron (III) chloride (FeCl3) solution to produce solid lead (II) chloride (PbCl2) and iron (III) nitrate solution, Fe(NO3)3

3. Iron metal reacts with bromine gas to yield an iron (III) bromide liquid.

IV. Types of Chemical Reactions Reactions between chemicals are classified into six major types:

Type of Reaction General Equation Example

Synthesis H2(g) + O2(g) → H2O(g)

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Notes:

DecompositionH2O2(aq) → H2O(l) + O2(g)

Notes:

Combustion

CH4(g) + O2(g) → CO2(g) + H2O(g)

Notes:

Single Replacement

Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq)

Notes:

Double Replacement

NaOH(l) + MgCl2(l) → NaCl(s) + Mg(OH)2(l)

Notes:

Neutralization

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)

Notes:

Synthesis/Combination: A + B C ex) synthesis of sodium oxide

Decomposition: A B + C ex) decomposition of lithium nitride

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Combustion: CxHy + O2 CO2 + H2Oex) combustion of propane

Single Replacement: A + BC AC + Bex) reaction of zinc with hydrochloric acid

Double Replacement: AB + CD AD + BCex) reaction between silver nitrate and sodium iodide

Acid-Base Neutralization (type of DR): HA + BOH BA + H2Oex) reaction between sulfuric acid and sodium hydroxide

V. Redox Reactions

a. Redox is short for __________________ - __________________ in which _________________ are

transferred from one chemical species to another

b. You can identify a redox reaction by a ____________ in ________________ ____________ (or

oxidation state)

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i. The oxidation number of an element represents the ____________ of electrons that atom

________ or ____________ when joining with other atoms in a compound

c. Rules for Assigning Oxidation Numbers

i. Atoms in their elemental form (ex: Ca, N2) are always equal to their ____________

ii. In a molecule, the _______ of all oxidation numbers MUST equal the ____________

Always true

Hydrogen

Oxygen

Group 1 metals

Group 2 metals

Usually but not always

true

Halogens (Grp 17)

Group 16

Group 15

Examples

Fe Fe2O3 O2 SO42- MnO4

-

Practice Assigning Oxidation Numbers

Zn H+ Zn2+ H2 Cu

NH4+ CO2 H2O CO NaNO3

d. Oxidation-Reduction

i. Reduction is a _______________ in oxidation number by ____________ electrons

ii. Oxidation is an ______________ in oxidation number by ____________ electrons

LEO the lion goes GERLEO = losing electrons oxidation

*Start with the elements you know to always be true, then use algebra to calculate the remaining oxidation numbers based on the charge of the entire compound

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GER = gaining electrons reductioniii. Oxidation and reduction ____________ go together.

For something to be reduced, something else must be oxidized

Examples Identifying Element Oxidized/Reduced

4Fe + 3O2 2Fe2O3

Oxidized:Reduced:

SO32- + MnO4

- SO42- + Mn2+

Oxidized:Reduced:

Practice Identifying Element Oxidized/Reduced

Zn + 2H+ Zn2+ + H2

Oxidized:Reduced:

Cu + 2Ag+ Cu2+ + 2Ag

Oxidized:Reduced:

KClO3 + HBr Br2 + H2O + KCl

Oxidized:Reduced:

CO2 + H2 CO + H2O

Oxidized:Reduced:

VI. Balancing Equationsa. Law of Conservation of Mass – mass is ______________ created nor destroyed in a chemical reaction

o ________ number of atoms of each element in ________ reactants and products

b. Steps in balancing equations: USE PENCIL!!!!!

1. Write the equation for the reaction

2. Balance compounds according to the law of conservation of mass using _______________________8

a. Balance _____ and _____ atoms LAST

b. FIRST, balance elements which appear only ________ on each side of the equation

c. Balance different types of atoms one at a time

d. If a polyatomic is on ________ sides of the reaction, balance as a single unit (Chunk!)

3. __________ all atoms to ensure equation is balanced

c. There are two methods to balancing:

o ERP tables

o Drawing it out

d. For me, you do not need to include the coefficient “1” as it is implied

o However, the SOL will count it wrong if you leave the space blank rather than including the 1

ERP Examples:

Drawing Examples:

____ NaBr + ___ Cl2 ___ NaCl + ___ Br2

____ C3H6 + ____ O2 ____ CO2 + ____ H2O

___H2 + ___O2 ___H2O

___H2 + ___O2 ___H2O2

Element Reactants Products

H

O

Element

Reactants Products

H

O

Balancing Tip:If you get stuck while balancing, try multiplying all the coefficients by 2!

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____ NaOH + ____ BaSO4 ____ Na2SO4 + ____ Ba(OH)2

PRACTICE:Balance the equations below by writing the correct coefficient in the space before each formula. You do not need to include the coefficient “1”.

1.) ____ H2 + ____ Cl2 _____ HCl

2.) ____ Fe + ____ Cl2 ____ FeCl3

3.) ____ Fe + ____ O2 ____ Fe2O3

4.) ____ Zn + ____ HCl ____ ZnCl2 + ____ H2

5.) ____ Ca(NO3)2 + ____ H2SO4 ____ CaSO4 + ____ HNO3

6.) ____ Cu + ____ AgC2H3O2 ____Cu(C2H3O2)2 + ____ Ag

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