Chapter 8

What can chemical equations tell us?

How can we describe chemical reactions?

Before we start… Before we start…

In this chapter you MUST be able to name BOTH types of compounds- ionic and covalent. Be sure to brush up on naming as needed!You also MUST know which elements exist as diatomic molecules! (BrINClHOF)

Section 1: Describing Chemical Section 1: Describing Chemical ReactionsReactions

New substances are formed.Reactants = starting materials.Products = ending materials.Recall evidence of a chemical change/reaction:

1. Formation of a gas (bubbles/change in odor).2. Formation of a precipitate (solid).3. Change in energy: heat/light/sound given off

(change in temperature).4. Change in color.

Chemical reactions are not always visible.Properties of substances change during chemical reactions.

EquationsEquations

Word Equations: use names.Replace “and” with +Replace “yields”, “produces”, “forms” etc. with

Ex: methane and oxygen form carbon dioxide and water.methane + oxygen carbon dioxide + water

Chemical Equations: use formulas.Replace words with chemical formulas.

Ex: methane + oxygen carbon dioxide + water CH4 + O2 CO2 + H2O

Information in an EquationInformation in an EquationEquations are like recipes – they give necessary information:

Ingredients (substances involved)amounts

Can also show physical states and conditions needed:Symbol Meaning

(s), (l), (g) Substance in solid, liquid, or gas form

(aq) Substance in aqueous form (dissolved in water)

“Produces”, “yields”, etc. indicating results of reaction

Reversible reaction in which products can reform into reactants; final result is a mixture of products and reactants

Reactants are heated; temperature is not specified

Name or chemical formula of a catalyst, added to speed up a reaction

Specific temperature or pressure needed for this reaction

Δ heat

Pd

500 oC 2 atm

Practice ProblemsPractice Problems

1) Aqueous iron (II) chloride and lithium bromide react to form aqueous lithium chloride and iron (II) bromide. Write the word equation.

2) Solid calcium carbonate is heated and decomposes to form solid calcium oxide and carbon dioxide gas. Write the chemical equation. Include phases!

Section 1 HomeworkSection 1 Homework

Honors: pg. 266 #2,3,9,11,13,17(a,b)

Why must chemical equations be balanced?

How are chemical equations balanced?

Section 2: Balancing Chemical ReactionsSection 2: Balancing Chemical ReactionsLaw of Conservation of Mass!

There must be the same number of each atom on both sides.Change coefficients NOT subscripts!Ex:

Steps for Balancing EquationsSteps for Balancing Equations1. Write formulas for all chemicals.2. Count atoms.

• Listing #s of each atom on both sides is helpful.• Keep polyatomic ions as a group if they appear on

both sides.3. Insert coefficients.

• It often helps to balance H and O last.• Try odd-even technique: place an even coefficient

in front of a chemical that has an odd # of atoms- makes all atom #’s even.

4. Verify Results.• Check #’s of atoms to make sure they’re equal!

Practice Problem #1Practice Problem #1Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.

(1)Write equation: Fe2O3 + H2 Fe + H2O(2)Count # atoms on each side:

(3) Balance # atoms on each side.(4) Double check your answer:

Fe2O3 + H2 Fe + H2O

Fe: Fe: O: O: H: H:

Fe: Fe: O: O: H: H:

Practice Problem #2Practice Problem #2The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write a balanced equation for this reaction.

Practice Problem #3- Using Practice Problem #3- Using FractionsFractionsSometimes it is helpful to use fractions as

coefficients when balancing equations.This can help you to arrive at the correct coefficients more quickly.Ex: C6H14 + O2 CO2 + H2O

It is easy to first balance the C and H atoms:C6H14 + O2 6CO2 + 7H2O

Try using a fraction to balance the O atoms:C6H14 + 19/2 O2 6CO2 + 7H2ONow multiply all coefficients by 2 to get whole #s.2C6H14 + 19O2 6CO2 + 7H2O

How can chemical equations be classified and how is this used to predict products?

Section 3: Classifying Chemical Section 3: Classifying Chemical ReactionsReactionsClassifying reactions allows us to better predict

products. We will look at five types: combustion, synthesis, decomposition, single displacement, and double displacement.

More than these five types exist.Some fall into more than 1 type.Some don’t fall into any type.

CombustionCombustionGeneric formula: AB + O2 CO2 + H2O

AB is a hydrocarbon (H and C bonded together).O may be present too.

Always form CO2 and H2O.

Examples:CH4 + O2 CO2 + H2OC6H6 + O2 CO2 + H2O

Synthesis (Addition)Synthesis (Addition)Generic Formula: A + B AB

Can be element + element yielding one compound. Al + O2 Al2O3

Can be compound + compound yielding one compound.

water + metal oxide metal hydroxide:H2O + CaO Ca(OH)2

water + nonmetal oxide acid:H2O + SO3 H2SO4

ammonia + acid ammonium salt:NH3 + HCl NH4Cl

DecompositionDecompositionGeneric Formula: AB A + B

Can be a binary compound yielding two elements.NaCl Na + Cl2

Can be a ternary compound.metal chlorate metal chloride and oxygen:

KClO3 KCl + O2

metal carbonate metal oxide and carbon dioxide:CuCO3 CuO + CO2

metal hydroxide yielding a metal oxide and water:Ca(OH)2 CaO + H2O

acid yielding nonmetal oxide + water:H2SO4 SO3 + H2O

PracticePractice

Name the type of reactions listed below and predict the product(s) for each:

1) Sr + O2

2) C3H6 + O2

3) Al(OH)3

4) CO2 + H2O

SrO

H2O + CO2

Al2O3 + H2O

H2CO3

Single Displacement Single Displacement When A is a metal: A + BC AC + B

If metal A is more reactive than metal B it displaces B’s spot in the compound:

Cu + AgNO3 Cu(NO3)2 + AgIf metal B is more reactive than metal A, no reaction occurs:

Cu + HCl no reaction (NR)

METAL REACTIVITIESLi > Rb > K > Ba > Sr >Ca > Na > Mg > Al > Mn >

Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H2 > Sb > Bi >Cu > Hg > Ag > Pt > Au

metalnonmetal

Single Displacement continuedSingle Displacement continuedWhen A is a nonmetal: A + BC BA + C

If nonmetal A is more reactive than nonmetal C it displaces C’s spot in the compound:

Cl2 + KBr KCl + Br2

If nonmetal C is more reactive than nonmetal A, no reaction occurs:

Cl2 + KF no reaction (NR)

NONMETAL REACTIVITIESF2 > Cl2 > Br2 > I2

metal nonmetal

Double Displacement Double Displacement Generic Formula: AB + CD AD + CB

When a compound plus a compound yields two new compounds. The metals ‘switch partners’ with the nonmetals.

H2SO4 + NaOH H2O + Na2SO4

More Practice ProblemsMore Practice ProblemsPredict the product(s) and write a balanced equation for the reaction of potassium with chlorine.

Magnesium is added to a solution of lead (II) nitrate. Will a reaction happen? If so, write the equation and balance it.

Additional Practice: pg.279 #1-4 and pg.282 #1-3

Why are some parts of a reaction left out?

Section 4: Writing Net Ionic EquationsSection 4: Writing Net Ionic EquationsIonic compounds dissolve in water ions separate and spread out.

Section 4: Writing Net Ionic EquationsSection 4: Writing Net Ionic EquationsAs long as a compound does not form a solid (precipitate), pure liquid, or gas, it will exist as ions in water, NOT as a compound.

Ions that do not form a solid, pure liquid, or gas are called spectator ions (remain as ions in solution).

Do not participate in the reaction.Use solubility rules to determine if a compound will remain as a solid in water (pg. 288).

Write total ionic equation (all ions present).Cross out all spectators that appear on BOTH sides of the equation.

Write final answer with remaining species- this is the net ionic equation.

ExampleExamplePotassium iodide solution + lead (II) nitrate solution ?

Double displacement:KI (aq) + Pb(NO3)2 (aq) ?

KI (aq) + Pb(NO3)2 (aq) KNO3 (?) + PbI2 (?)Use solubility rules or clues in question.

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

(s)Total Ionic:

2 K+ (aq) + 2 I - (aq) + Pb+2 (aq) + 2 NO3- (aq)

2 K+ (aq) + 2 NO3

- (aq) + PbI2 (s)Net Ionic:

2 K+ (aq) + 2 I - (aq) + Pb+2 (aq) + 2 NO3- (aq)

2 K+ (aq) + 2 NO3

- (aq) + PbI2 (s)

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

This is the reaction taking place.

Steps for Writing Net Ionic Steps for Writing Net Ionic EquationsEquations1. List what you know.

• Identify the type of reaction.• Identify reactants (and products if provided).

2. Write a balanced chemical reaction.• Use type to predict products (if not told what they are).• Use solubility rules to predict states of matter.

3. Write total ionic equation.• Separate ions (anything still in solution = aq).• Do not separate any solids, liquids, or gases!

4. Find the net ionic equation.• Cancel out any spectator ions and write remaining species.• Double check that equation is balanced.

Practice Problem #1Practice Problem #1Write the net ionic equation for the reaction that occurs when zinc is placed in a copper (II) sulfate solution.

1) Reaction type: 2) Balanced Equation:

3) Total Ionic Equation:

4) Net Ionic Equation: