chapter 7: chemical reactions - moorpark...

C h a p t e r 7 , C h a p t e r 1 6 ( 2 - 5 ) : C h e m i c a l R e a c t i o n s P a g e | 1

Chapter 7: Chemical Reactions

Read Chapter 7 and Check MasteringChemistry due dates.

Evidence of Chemical Reactions:

Changes occur in the chemical composition

Color change

Formation of solid

Formation of gas

Emission of light

Change in temperature without

externally adding or removing heat.

Try this #1: Are you fooled into thinking all

changes are evidence of chemical reactions

Is boiling water (liquid to gas) a chemical change?

Is separation of CuSO4 from sand by dissolving the CuSO4 in water and filtering the sand a chemical change?


The Chemical Equation:

Reactants Products

Phases: solid (s), liquid (l), gas (g), aqueous (aq)

Balancing Chemical Equations:

Balance the same number of atoms on either side

Total charges must also balance on each side

Once the formulas are correctly written, add numbers to coefficients (never change a

subscript to balance)

Process:

Write skeletal equation with correct chemical formulas as reactants and

products

Start with a substance with the most atoms and subscripts

If an element occurs in only one compound on both sides, that element

should be balanced first.

If more than one choice is available, balance metals before nonmetals

Balance a free element last, adjust the coefficient on the fee element

Remove fractions by multiplying through by the denominator

Check

The number of a particular type of atom within a chemical formula

embedded in an equation is obtained by multiplying the subscript for

the atom by the coefficient for the chemical formula.

If there is no coefficient or subscript, a 1 is implied.

An example of the balanced equation for the combustion of natural

gas follows:


Try this #2:

Practice balancing the following:

a) carbon dioxide gas and water forms carbonic acid

b) C3H8 (g) + O2 (g) CO2 (g) + H2O (l)

c) Pb(NO3)2 (aq) + K2S (aq) PbS (s) + KNO3 (aq)

d) solid zinc is added to hydrochloric acid to produce hydrogen gas and

aqueous zinc chloride

e) NH3 (g) + O2 (g) NO2 (g) + H2O (l)

f) aqueous acetic acid and potassium sulfite react to form aqueous potassium

acetate, water and sulfur dioxide gas.


Electrolytes in Aqueous Solution:

Pure water does not conduct electricity.

If charged ions are dissolved in water it will conduct

electricity.

Strong Electrolytes will dissociate into its ions in an

aqueous solution and are written as separated ions in

the total and net ionic reactions.

Examples: Strong acids, Strong Bases, Soluble salts.

Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3

Strong Bases: soluble hydroxides from Group IA (not including H) and

Group IIA, not including the top two: LiOH, NaOH, KOH, RbOH,

Ca(OH)2, Sr(OH)2, Ba(OH)2

Soluble Salts:

Ionic compounds that contain cations from Group 1A; Li+, Na+, K+, or

NH4+ or the anions NO3

-1, ClO4-1, C2H3O2

-1 are mostly soluble.

Compounds with Cl-1, Br-1, I-1 are soluble except with Ag+, Hg2+2, Pb+2

Compounds with SO4-2 are soluble except Sr+2, Ba+2, Pb+2 or Ca+2.

Weak Electrolytes will partially dissociate into its ions in an aqueous solution, but are

written together in an ionic equation. Weak electrolytes are the weak acids and

weak bases such as HC2H3O2 or NH3


Nonelectrolytes will stay together in an aqueous solution. Nonelectrolytes are the

insoluble salts [solids], and molecular gases and liquids.

Solubility Rules: familiarize yourself with the top portion of ions mostly soluble


Writing Molecular, Ionic, and Net ionic equations:

Example: For the double displacement reaction of lead (II) nitrate reacting with potassium iodide.

Whole equation: Balanced

Pb(NO3)2 (aq) + 2 KI (aq) PbI2 (s) + 2 KNO3 (aq)

Total ionic equation:

Pb+2(aq) + 2 NO3-1

(aq) + 2 K+1(aq) + 2 I-1

(aq) PbI2 (s) + 2 K+1(aq) + 2 NO3

-1(aq)

Identify the spectator ions and leave them out when writing the net ionic eq.

Net ionic equation:

Pb+2 (aq) + 2 I-1 (aq) PbI2 (s)

This is a double displacement reaction and specifically a precipitation reaction.

(D-D) double displacement type reactions: AB + CD AD + CB

A chemical composition change has occurred. The visible evidence of this change is the

formation of yellow solid. Two colorless liquids react to form the new yellow solid PbI2.

Try this #3:

Follow the rules above to write the Molecular, Ionic, and Net ionic equations for the

reaction of aqueous calcium chloride and aqueous potassium carbonate.

Whole equation:

Total ionic equation:

Identify the spectator ions and leave them out when writing the net ionic eq.

Net ionic equation


Classifying Chemical Reaction Types:

(D-D) double displacement

(N) neutralization or acid-base,

(P) precipitation

(R) redox or oxidation-reduction

(SR) single replacement

(C) combustion

(G) gas evolution

(Syn) synthesis or combination

(D) decomposition

Classifying and Predicting Products and Chemical Reactions:

The following examples will help you classify the type of reaction and predict the

expected products.

(D-D) double displacement: AB + CD AD + CB

A double displacement reaction starts with two ionic compounds in which the ions

exchange to produce new balanced ionic compounds. Always write the cation

before the anion and verify that the net charge of each compound is zero. Ionic

compounds may be acid, base, or salt. Oxidation charges do not alter in double

displacement reactions so this type will never be a redox reaction.

Driving forces for double displacement reactions include

formation of a solid (P) Precipitation, Check solubility rules

formation of water (N) Neutralization or Acid-Base Reaction

formation of a weak electrolyte (WE)

Reactions do not always occur when mixing two aqueous solutions. (NR) no reaction

(P) Formation of a new solid in a double displacement reaction when there is

no solid on the reactant side is called PRECIPITATION.

Ni(NO3)2 (aq) + Na2S (aq) NiS (s) + 2 NaNO3 (aq) DD,P


(N) Formation of water in a double displacement reaction is called

NEUTRALIZATION (also known as Acid-Base reaction)

3 KOH (aq) + H3PO4(aq) K3PO4 (aq) + 3 H2O (l) DD,N

(WE) Formation of a WEAK ELECTROLYTE, generally a weak acid, produced

from a double displacement reaction

Al(C2H3O2)3 (aq) + 3 HCl (aq) AlCl3 (aq) + 3 HC2H3O2 (aq) DD,WE

(NR) When all ionic products are strong electrolytes, there is NO REACTION.

FeBr3 (aq) + 3 LiNO3 (aq) 3LiBr (aq) + Fe(NO3)3 (aq) NR

(G) Gas Evolution:

Several common compounds are in the gas phase. You should recognize the

following as gases.

CO2, SO2, CH4, NH3, H2S, H2, N2, O2, F2, Cl2, NO, NO2

Special cases of (G) Gas Evolution in (DD) Double Displacement:

There are three common products that further decompose leading to three products

in place of just the two products in a double displacement reaction. They are as

follows.

NH4OH (aq) NH3 (g) + H2O (l)

H2SO3 (aq) SO2 (g) + H2O (l)

H2CO3 (aq) CO2 (g) + H2O (l)


The double displacement reactions below show examples of the decomposition of

one of the ionic products. The driving forces include both formation of water and a

gas, because water is formed these can be labeled Neutralization reactions. The last

one is DD, N, and P.

K2CO3 (aq) + 2HCl (aq) H2CO3 (aq) + 2 KCl (aq)

K2CO3 (aq) + 2HCl (aq) CO2 (g) + H2O (l) + 2 KCl (aq)

Na2SO3 (aq) + 2HCl (aq) H2SO3 (aq) + 2 NaCl (aq)

Na2SO3 (aq) + 2HCl (aq) SO2 (g) + H2O (l) + 2 NaCl (aq)

(NH4)2SO4 (aq) + Ba(OH)2 (aq) 2 NH4OH (aq) + BaSO4 (s)

(NH4)2SO4 (aq) + Ba(OH)2 (aq) 2 NH3 (g) + 2 H2O (l) + BaSO4 (s)

Try this #4:

Write an equation for the precipitation reaction that occurs (if any) when

solutions of sodium carbonate Na2CO3(aq) and copper(II) chloride CuCl2(aq)

are mixed.

Predict the products and balance for the reaction that geologist use to test for

carbonates in rock or mineral samples…

HNO3 (aq) + CaCO3 (s)

(marble)


(Syn) Synthesis or combination: A + B AB

A synthesis reaction starts with two or more substances and creates a single

compound product. The reverse of a synthesis reaction is Decomposition.

Remember which elements are diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2. Know

the elements in their pure form: gas (red), solid (black), and liquid (blue), by color

on the periodic table in the classroom.

a) two elements (metal plus nonmetal) ionic compound.

Na (s) + Cl2 (g) NaCl (s) Balance this

b) metal oxide and water base (metal hydroxide)

BaO (g) + H2O (l) Ba(OH)2 (aq)

c) nonmetal oxide and water acid

CO2 (g) + H2O (l) H2CO3 (aq)

Try this #5:

Balance the synthesis reactions…

Al (s) + O2 (g) Al2O3 (s)

Na2O (s) + H2O (l) NaOH (aq)


(D) Decomposition: AB A + B

A decomposition reaction starts with one reactant and breaks up into two or more

substances. The reverse of a decomposition reaction is synthesis. Remember the

diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2.

a) Water can be broken into its elements by electrolysis

b) ionic compound two elements (metal plus nonmetal)

2 Fe2O3 (s) 4 Fe (s) + 3 O2 (g)

c) metal carbonate metal oxide and carbon dioxide

CaCO3 (s) CaO (s) + CO2 (g)

d) metal bicarbonate metal carbonate + water + carbon dioxide

2 Al(HCO3)3 (s) Al2(CO3)3 (s) + 3 H2O (l) + 3 CO2 (g)

e) metal connected to halogen with oxygen metal halide + oxygen

Ca(BrO3)2 (s) CaBr2 (s) + 3 O2 (g)

f) hydrated salt anhydrous salt plus water

CuSO4.5H2O (s) CuSO4 (s) + 5 H2O (l)


Try this #6:

Balance the decomposition reactions that occur after heating…

CoCl2.6H2O (s) CoCl2

(s) + 6H2O (l)

KClO3 (s) KCl (s) + O2 (g)

NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g)

(R) Redox or oxidation-reduction reactions:

Redox reactions transfer electrons. A way to tell that a redox reaction takes place is

to check for element charges and see if they change from reactant side to product

side. If on one side of the reaction an atom or molecule has a zero charged element

and on the other side of the reaction the same atom is now part of a compound or an

ion, then electrons have been moved. Some synthesis and decomposition reactions

are redox. All combustion and single replacement reactions are redox reactions.

Oxidation Reduction

increases oxidation number reduces oxidation number

lose electrons gain electrons

2 Cl-1 Cl2 + 2 e- K+ + 1 e- K

OIL RIG

Oxidation is losing electrons reduction is gaining electrons

Leo the lion growls Ger

Lose electrons is oxidation gain electrons is reduction

(C) Combustion: elements burn with O2 gas to produce oxides,

Common products include: CO2, H2O, NO2, SO2.

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)


Try this #7:

Predict the products and balance

C4H10 (l) + O2 (g)

C6H14S (s) + O2 (g)

C12H22O11 (s) + O2 (g)

NH3 (g) + O2 (g)

Another Redox [Oxidation-Reduction] type reaction: Chem 12: identify classification or

balance, but not necessary to predict the products for this class.

(SR) Single Replacement: A + BC AC + B

The more active element will have a partner, less active is alone.

Activity series:

Au<Hg<Ag<Cu<H2<Pb<Sn<Ni<Fe<Cr< Zn<Mn<Al< Mg< Na<Ca< K<Li

Try this #8:

Predict the products if a reaction occurs or write NR for no reaction…

Zn(NO3)2 (aq) + Cu (s)

Cu(NO3)2 (aq) + Zn (s)

Redox Applications: Combustion, Bleaching, Batteries, Fuel cells, Metallurgy, Corrosion, Respiration


Practice Problems:

1. List the elements that are diatomic.

2. Name several driving forces for a chemical reaction.

3. Name several signs of evidence that would indicate a chemical reaction happened.

4. What information can one obtain from a balanced chemical equation?

5. For the following double-displacement reaction:

a) Complete the whole equation by including the products and balance the

equation. Include the physical states in all the equations.

NaCl (aq) + AgNO3 (aq)

b) Write the balanced total ionic equation for the above reaction. Include

charges on ions.

Circle the spectator ions in part b?

c) Write the balanced net ionic equation for this reaction.

d) What is/are the driving force(s) for this reaction?

6. Crude gunpowders often contain a mixture of solid potassium nitrate and charcoal

(solid carbon). When such a mixture is heated until a reaction occurs, a solid residue

of potassium carbonate is produced. The explosive force of the gunpowder comes

from the fact that two gases are also produced, carbon monoxide and nitrogen,

which increase in volume with great force and speed. Write the balanced chemical

equation for the reaction.


7. Balance and Classify in as many ways possible the following reactions.

Possible classifications:

(D-D) double displacement

(N) neutralization or acid-base,

(P) precipitation

(R) redox or oxidation-reduction

(SR) single replacement

(C) combustion

(G) gas evolution

(Syn) synthesis or combination

(D) decomposition

(NR) no reaction

a) Mg(ClO3)2 (s) MgCl2 (s) + O2 (g)

b) N2 (g) + O2 (g) N2O5 (g)

c) C6H6 (l) + O2 (g) CO2 (g) + H2O (g)

d) KOH (aq) + H2SO4(aq) K2SO4 (aq) + H2O (l)

e) AgNO3 (aq) + Na2CrO4 (aq) Ag2CrO4 (s) + NaNO3 (aq)

f) aqueous silver nitrate and solid copper reacts to form aqueous copper (II)

nitrate and solid silver.

g) solid magnesium carbonate heated produces carbon dioxide gas and solid

magnesium oxide

h) C3H8 (g) + O2 (g) CO2 (g) + H2O (g)

i) Fe (s) + Br2 (l) FeBr3 (s)

j) H2SO4(aq) + Na2CO3(aq) Na2SO4(aq) + H2O(l) + CO2(g)


k) Al2(CO3)3 (s) Al2O3 (s) + CO2 (g)

l) HC2H3O2 (aq) + Mg (s) H2 (g) + Mg(C2H3O2)2(aq)

m) Ni(NO3)2 (aq) + K2S (aq) NiS (s) + KNO3 (aq)

n) KOH (aq) + (NH4)2SO4(aq) NH3 (g) + K2SO4(aq) + H2O (l)

o) Al (s) + O2 (g) Al2O3 (s)

p) Fe(ClO3)3 (s) FeCl3 (s) + O2 (g)

q) Ag (s) + HI (aq) AgI (s) + H2 (g)

r) H2O (l) + N2O3 (g) HNO2 (aq)

s) aqueous sodium hydroxide and sulfuric acid react to form aqueous sodium

sulfate and liquid water

t) octane gas and oxygen gas react to form carbon dioxide gas and water.

u) aqueous potassium sulfide and lead II nitrate react to produce solid lead II

sulfide and aqueous potassium nitrate.

v) Aqueous nitric acid is added to aqueous sodium bicarbonate, the reaction

produces an aqueous salt, plus a gas and a liquid.


8. Complete and Balance the following chemical reactions.

Include the state that the substances are in, (s), (l), (g), or (aq). If no reaction in a

double displacement then write No reaction.

a) Combustion reaction:

C7H16 (s) + O2 (g)

b) Double Displacement reaction:

aqueous sodium hydroxide is added to aqueous copper (II) chloride

c) Double Displacement reaction:

aqueous sulfuric acid is added to aqueous ammonium carbonate

d) Double displacement reaction:

KNO3 (aq) + NH4Br (aq)

e) Double Displacement reaction:

HCl (aq) + Ba(OH)2 (aq)

f) Combustion

Liquid pentane, C5H12, reacts with atmospheric oxygen

chapter 7: chemical reactions - moorpark...

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