Chapter 10

Chemical Reactions

Evidence of Chemical Change

A chemical reaction is a process by which the atoms of one or more substances are rearranged to form different substances.

4 Indicators

Change in color

Change in temperature or energy

Production of a gas

Formation of a precipitate

Representing Balanced Chemical Equations

Reactants Product

Coefficient

)(2)(2)(2 22 lgg OHOH

Subscript Physical state

Symbols

+ Separates two or more products or reactants

Separates reactants from products

(s) Solid (l) Liquid (g) Gas (aq) Aqueous

Balancing Chemical Equations

A written chemical equation must abide by the law of conservation of matter

Make sure that both sides of an equation have an equal number of each type of atom represented.Balance equations by adding coefficients.Never mess with subscripts

Examples

NaBrMgClMgBrNaCl ________ 22

FeMgClFeClMg ________ 23

Na

Cl

Mg

Br

FeMgClFeClMg ________ 23

Mg

Fe

Cl

Strategies for Balancing Chemical Equations

1. The even/odd combination

Make the subscript of one, the coefficient of the other and vice versa.

Iron (III) oxide Iron + Oxygen

232 3402 OFeFe

Strategies Continued

2. Balance groups as a whole if the elements of the group are only represented in the group on each side of the equation.

MgOHAlAlOHMg __)(____)(__ 32

Mg

OH

Al

Strategies Continued

3. Balancing Hydrocarbon Combustion Reactions

The first step is to add a coefficient to the hydrocarbon so that the total number of hydrogens in the molecule is divisible by four. Then, balance the product side of the equation before finishing up with oxygen.

0____0____ 2225 HCOCH

C

H

O

Things to Keep in Mind

Again, do not mess with subscriptsIn the final solution, the coefficients have

to be in the lowest whole number ratio.

If at first you don’t succeed, try, try again! Most of the solutions to these problems come from trial and error.

OHOH 222 424 OHOH 222 22

Writing Chemical Equations

Iron combines with oxygen to form solid iron (III) oxide

)(32)(2)( 234 sgs OFeOFe All metals are represented by their symbol in the periodic

table with NO subscripts.

All elemental gases are diatomic (BrINClHOF)

Use your ion table or molecular name to figure out the chemical formula of compounds in your equation

Balance the equation

Note the physical state of each substance in the equation

Practice Problem

Aqueous calcium chloride combines with aqueous silver nitrate to form aqueous calcium nitrate and solid silver chloride.

Another Practice Problem

Aluminum combines with aqueous hydrochloric acid (HCl) to form aqueous aluminum chloride and hydrogen gas.

Hint: Write the formula for each substance as if it were independent of the other substances in the equation.

Chapter 10 Checklist

Balancing equationsWriting chemical equationsDetermining the physical state of reactants

and productsDetermining reaction typePredicting products of a reactionDetermining if a reaction will occur

Writing Chemical Equation Quiz – Tuesday 3/24

Physical States

Atoms Metals – All solid except mercury (liquid) Nonmetals – all gases except bromine (liquid)

and iodine (solid)

Compounds Covalent compounds – usually a liquid or gas, but not predictable Acids – always aqueous (aq) Ionic compounds – refer to solubility table

Soluble (dissolves) – aqueous (aq) Insoluble (doesn’t dissolve) – solid (s)

Chapter 10 Checklist

Balancing equationsWriting chemical equationsDetermining reaction typePredicting products of a reactionDetermining the physical state of reactants

and productsDetermining if a reaction will occur

Using a solubility Table for Ionic Compounds

General Rules Table• Look up the solubility for a compound’s anion

• If the substance is insoluble then it is a solid• If the substance is soluble it is aqueous• Check to see if the cation in your compound is in the

exception column.

Common Ion Solubility Exceptions

CO32- insoluble Group IA and NH4

+

NaCO3

Final Answer: NaCO3(aq)

Determine the physical states

CaSO4

(NH4)2S

K3PO4

CuC2H3O2

Solid

Aqueous

Aqueous

Aqueous

Practice Problem

Write the equation Balance the equation Note the physical state of each substance

Potassium chromate combines with lead (II) nitrate to form potassium nitrate and lead (II) chromate

Types of Chemical Reactions – 5 General Formulas

CombustionCxHy + O2 CO2 + H20

SynthesisA + B AB (Two elements combine to form a compound)

DecompositionAB A + B (One compound splits to form two compounds)

Always the products of these combustion reactions

Reactions Cont.

Single Replacement (Single Displacement)A + BC AC + B Metals replace metals

Non-metals replace non-metals

Double Replacement (Double Displacement)AB + XY AY + XB Compounds switch partners

Pre-class Question 3/25

Identify the type of reaction

)(2)()(32

)(4)(42)(2

)()(2)(

)(2)(2)(2)(104

)(4)()(342)(

342

2

22

0108132

32)(3

)(

gss

aqaqaq

sgs

lggg

ssaqs

OFeOFe

LiClCaCrOCrOLiCaCl

MgOOMg

HCOOHC

BaSOFeSOFeBa

s

Combustion Decomposition Single replacememt

Synthesis Double Replacement

Chapter 10 Checklist

Balancing equationsWriting chemical equationsDetermining the physical state of reactants

and productsDetermining reaction typePredicting products of a reactionDetermining if a reaction will occur

Predicting Products of Hydrocarbon Combustion Reactions

With hydrocarbons, the products are always CO2 (g) and H2O(l)

)(2)(188 __ gg OHC

Predicting Products of Synthesis ReactionsFor Synthesis Reactions

For metals that only form one cation, determine the charge on the ion of each element (metallic and non-metallic) and form a compound from the two ions.

If one of the elements forms more than one cation or 2 nonmetals are combined, the products can only be predicted if the ratio of elements in the compound are given

)(2)( gs ClAg

Predicting Products of Decomposition Reactions

)(aqHCl

Predicting Products of Double Replacement Reactions

• Rearrangement of cations and anions to form 2 new compounds.

• Reaction occurs when a solid or water is produced from aqueous reactants

)(432 )( aqPOLiMgClaq

Predicting Products of Single Replacement Reactions

Refer to the activity series chart to determine if the reaction will occur.

Metals replace metals. Nonmetals replace non-metals

)(3)(

)(2)(2

aqs

aqg

AlClNa

CaBrCl