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Chapter 08 - Chemical Equations

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Foundations of College Chemistry, 14th Ed.

Morris Hein and Susan Arena

Flames and sparks result when aluminum foil is dropped into liquid bromine.

8 Chemical Equations

(2)

Reactants: substances consumed during the reaction. Products: substances formed during the reaction.

Atom balance must be maintained in all chemical reactions. All atoms from reactants must appear as part of products.

a A + b B c C + d D

Chemical Equations

• Chemical reactions are processes in which one set

of chemicals are converted to a new set of chemicals

• Chemical reactions are described by chemical

equations.

(3)

Evidence for Chemical

Reactions

• A gas is produced.

• A precipitate is formed.

(4)

General Structure of Chemical Equations:

1. Reactants and products are separated by an arrow. Reactants are on the left side of the arrow,

products are on the right.

a A + b B c C + d D

Reactants Products

2. Whole number coefficients are placed in front of substances to balance the atoms in the equation. The numbers indicate the units of the substance reacted or formed during the reaction.

The coefficient 1 is not written in a balanced equation.

Chemical Equations

(5)

General Structure of Chemical Equations:

3. Information about the reaction (temperature, time) may be placed above or below the reaction arrow.

4. The physical state is written in brackets after the formula of the substance.

a A + b B Δ c C + d D

Δ indicates heat

(g) for gas, (l) for liquid, (s) for solid, (aq) for aqueous

a A (s) + b B (l) c C (g) + d D (s)

Chemical Equations

(6)

Symbol Summary

Symbol Significance

Produces (points towards products) (s) Solid (written after substance)

(l) Liquid (written after substance) (g) Gas (written after substance)

(aq) Substance dissolved in an aqueous solution

Heat is added (above or below reaction arrow) Δ

Chemical Equations

(7)

In an ordinary chemical reaction, the total mass of

reacting substances is equal to the total mass of

products formed.

In any chemical reaction:

Mass of reactants = Mass of products water hydrogen + oxygen 100.0 g 11.2 g 88.8 g

100.0 g total of products reactants

Law of Conservation of Mass

(8)

Chemical Equations

• N

2

(g) + 3 H

2

(g)

2 NH

3

(g)

• must be balanced to satisfy Law of

conservation of mass

• N

2

2

(9)

Diatomic Elements

When an equation says “oxygen” or any

(10)

Copper(II) oxide reacts with ammonia (NH

3

)

to yield copper, nitrogen gas, and water.

(11)

Lead(II) nitrate reacts with potassium

chromate to form lead(II) chromate

(yellow ppt.) and potassium nitrate.

Hydrochloric acid reacts with sodium

(12)

Zinc metal reacts with hydrochloric

acid to produce zinc chloride and

hydrogen gas.

Potassium chlorate when heated,

(13)

Hexane(C

6

H

14

) burns in oxygen gas to

form carbon dioxide and water.

Vinegar(acetic acid) reacts with

baking soda (sodium bicarbonate) to

produce carbon dioxide gas, sodium

acetate, and water.

Ammonia reacts with oxygen gas to

(14)

Iron(III) chloride reacts with ammonium

hydroxide to form iron(III) hydroxide

(brown ppt.) and ammonium chloride.

Barium hydroxide and ammonium

(15)

Some more examples

N

2

+ H

2



NH

3

Be

2

C + H

2

O



Be(OH)

2

+ CH

4

HCl + CaCO

3



CaCl

2

+ H

2

O + CO

2

(16)

Reactions are classified into subtypes to aide in predicting the products of chemical reactions.

Reactions are classified into five major categories:

1. Combination reactions 2. Decomposition reactions

3. Single displacement reactions 4. Double displacement reactions

5. Oxidation-reduction (redox) reactions (Chapter 17)

Types of Chemical Equations

(17)
(18)

Classifying Reactions by what Atoms

Do

(19)

Two reactants combine to give a single product.

where A or B are elements/compounds and AB is a compound.

A + B AB

Representative Examples

metal + nonmetal salt 2 Na (s) + Cl2 (g) 2 NaCl (s)

CaO (s) + H2O (l) Ca(OH)2 (aq)

metal oxide + water metal hydroxide

Violent reaction occurs when Al and Br2 react to form AlBr3.

2 Al (s) + 3 Br2 (l) 2 AlBr3 (s)

Combination Reactions

(20)
(21)

Classifying Reactions by what Atoms

Do

(22)

A single reactant breaks down (decomposes) into two or more products .

AB A + B

Representative Examples

Metal oxides often decompose when heated.

CaCO3 (s) CaO (s) + CO2 (g) Carbonates form CO2 when heated. 2 PbO2 (s) 2 PbO(s) + OΔ 2 (g)

H2O2 decomposes to steam (H2O (g)) and O2. 2 H2O2 (l) 2 H2O (g) + O2 (g)

Decomposition Reactions

(23)

Classifying Reactions by what Atoms

Do

• Single Displacement

(24)

One element (A) reacts with a compound (BC) to replace one element in the compound, giving a new element (B)

and a different compound (AC). A + BC B + AC

where A and B are metals and A is more reactive. or

A + BC C + AB

where A and C are halogens and A is more reactive.

Zn reacts with HCl, resulting in H2 gas evolution. Example

Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)

Single Displacement Reactions

(25)

Table listing in order of decreasing reactivity of various elements.

More reactive elements replace less reactive ones. 2 Al (s) + 3 CuCl2 (s) 2 AlCl3 (aq) + 3 Cu (s)

2 Ag (s) + 3 CuSO4 (s) No Reaction

Activity Series

(26)
(27)

Metal + acid hydrogen + salt

Where A and B are metals and A is more reactive:

2 Al (s) + 3 H2SO4 (aq) Al2(SO4)3 (aq) + 3 H2 (g)

Metal + water hydrogen + metal hydroxide/oxide

2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g)

Metal (or halogen) + salt metal (or halogen) + salt

Fe (s) + CuSO4 (aq) Cu (s) + FeSO4 (aq)

Cl2 (g) + 2 KI (aq) I2 (s) + 2 KCl (aq)

General Types of Single

Displacement Reactions

(28)

Will a reaction occur between Ni and HCl? If so, write the balanced chemical equation.

Based on the reactivity series, Ni is more reactive than hydrogen, so a reaction occurs.

Ni (s) + HCl (aq) H2 (g) + NiCl2 (aq)

Will a reaction occur between Sn and AlCl3? If so, write the balanced chemical equation.

Based on the reactivity series, Sn is less reactive than Al, so no reaction occurs.

Sn (s) + AlCl3 (aq) No Reaction (NR)

Single Displacement Reactions

(29)

Cu( ) + AgNO

3

( )

Cr ( ) + NiCl

2

( )

Fe ( ) + HCl ( )

Cr ( ) + Zn(NO

3

)

2

( )

(30)

Two compounds exchange partners with one another to yield two new compounds.

AB + CD AD + CB

Physical evidence for a double displacement reaction include: heat evolution, formation of a precipitate

or gas production.

PbI2 precipitates from the reaction of Pb(NO3)2 with KI. Pb(NO3)2 (aq) + 2 KI (aq) PbI2 (s) + 2KNO3 (aq)

Double Displacement Reactions

(31)

acid + base salt + water + heat Acid/Base Neutralization

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) + heat

Metal oxide + acid salt + water + heat

CuO (s) + 2 HNO3 (aq) Cu(NO3)2 (aq) + H2O (l) + heat

Metal Oxide (base) + Acid

General Types of

Double Displacement Reactions

(32)

Product solubilities are based on the table in Appendix V Formation of a Precipitate

BaCl2 (aq) + 2 AgNO3 (aq) 2 AgCl (s) + 2 KNO3 (aq)

H2SO4 (l) + NaCl (s) NaHSO4 (aq) + HCl (g) Gas Formation

Insoluble products are indicated by (s)

A gas can also form from a secondary reaction after displacement

2 HCl (aq) + Na2CO3 (aq) 2 NaCl (aq) + H2CO3 (aq) H2CO3 (aq) H2O (l) + CO2 (g)

General Types of

Double Displacement Reactions

(33)

Na

2

S ( ) + ZnCl

2

( )

Mg(NO

3

)

2

( ) + NaOH ( )

AgNO

3

( ) + Na

2

SO

4

( )

(34)

NH

4

Cl ( ) + KOH ( )

HNO

3

( ) + NaC

2

H

3

O

2

( )

Figure

Table listing in order of decreasing reactivity  of various elements.

References

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