Chemical Equations: Chemical Equations: Predicting Types of Predicting Types of

Reactions and BalancingReactions and Balancing

I. Chemical EquationsI. Chemical Equations

A chemical equation represents a A chemical equation represents a chemical reaction – chemical reaction – Chemicals present before the reaction Chemicals present before the reaction

are shown to the left of the arrow and are shown to the left of the arrow and are called the are called the REACTANTSREACTANTS..

Chemical formed by the reaction are Chemical formed by the reaction are shown to the right of the arrow and are shown to the right of the arrow and are called the called the PRODUCTSPRODUCTS..

REACTANTS REACTANTS * PRODUCTS* PRODUCTS

* * arrowarrow – indicates direction of change – indicates direction of change and is read as “yields” or “produces”and is read as “yields” or “produces”

Example - CH4 + 2O2 CO2 + 2H2O

Reactants Yield Products

II. Predicting Whether a Reaction II. Predicting Whether a Reaction Will OccurWill Occur

A. Four Driving ForcesA. Four Driving Forces1.1. Formation of a Formation of a solidsolid (precipitate) (precipitate)

2.2. Formation of Formation of waterwater

3.3. Transfer of electronsTransfer of electrons

4.4. Formation of a Formation of a gasgas

B. If a driving force occurs the reaction B. If a driving force occurs the reaction will take place.will take place.

III. Classifying Types of III. Classifying Types of ReactionsReactions

Double Displacement: Double Displacement:

Single Displacement:Single Displacement:

Decomposition: Decomposition:

Synthesis:Synthesis:

Combustion:Combustion:

AB A + B

AB +YZ AZ + YB

A +YB Y + AB

A + B AB

CxHx + O2 CO2 + H2O

Reactants are: 2 compounds

Reactants are: 1 element & 1 Compound

Reactant is: 1 compound

Reactants are: 2 elements or 2 oxides

Reactants are: hydrocarbon and oxygen

Double Displacement Double Displacement reactionsreactions

Precipitation Reaction: Precipitation Reaction: Double Double Displacement reactions where the Displacement reactions where the driving force is formation of a driving force is formation of a solidsolid. .

Acid-Base/ Neutralization Acid-Base/ Neutralization Reaction: Reaction: Double Displacement Double Displacement reactions where the driving force is reactions where the driving force is formation of a formation of a liquidliquid. (water). (water)

Oxidation Reduction Oxidation Reduction reactionsreactions: (redox): (redox)

DDriving Force = Transfer of electronriving Force = Transfer of electron Always in single displacement reactionsAlways in single displacement reactions Sometimes in Synthesis and DecompositionSometimes in Synthesis and Decomposition Never in Double DisplacementNever in Double Displacement

  Example: Example:

Anytime a single element is present a reaction is also classified as redox

NaCl(aq) +Na(s) Cl2(g)2 2

NaCl(aq)+Na(s) Cl2(g) 22

Zn(NO3)2(aq) + 2 Na(s) 2NaNO3(aq) + Zn(s)

decomposition & redox

synthesis & redox

single displacement & redox

Learning CheckLearning CheckClassify the following reactions:2 KNO3 2 KNO2 + O2  

2 C2H2 + 5 O2 4 CO2 + 2 H2O 

CaO + H2SO4 CaSO4 + H2O

3 CaCl2 + 2 Na3PO4 Ca3(PO4)2(s) + 6 NaCl

2 Fe + 6 HC2H3O2 2 Fe(C2H3O2)3 + 3 H2

2 KCl + 3 O2 2 KClO3

decomposition & redox

combustion

Double displacement & acid/base

Double displacement & ppt

Single displacement & redox

Synthesis & redox

Evidence of Chemical ReactionsEvidence of Chemical Reactions

Four Four indicatorsindicators a chemical reaction has a chemical reaction has occurred:occurred: Color change - Color change - drasticdrastic Becomes Cloudy - Becomes Cloudy - Precipitate formsPrecipitate forms Bubbles - Bubbles - Gas formsGas forms Heat is produced or absorbed, Heat is produced or absorbed, or lightor light

The reactants and the products contain The reactants and the products contain the same atoms, but the chemical reaction the same atoms, but the chemical reaction has changed the way they are grouped.has changed the way they are grouped.

In a chemical reaction, atoms are neither In a chemical reaction, atoms are neither created nor destroyed, all atoms present created nor destroyed, all atoms present in the reactants must be present in some in the reactants must be present in some form in the products.form in the products.

There must be the same number of each There must be the same number of each type of atom on both sides of the type of atom on both sides of the equation.equation.

Balancing an equation makes sure that Balancing an equation makes sure that there is the same number and type of there is the same number and type of atom on both sides of the equation.atom on both sides of the equation.

Law of Conservation

The chemical equation for a reaction The chemical equation for a reaction provides us with three important provides us with three important pieces of information:pieces of information:

1.1. Identities Identities of the reactants and productsof the reactants and products

2.2. Relative Relative numbersnumbers of each atom of each atom

3.3. StateState of each reactant and product of each reactant and product

States of matter are shown with the States of matter are shown with the following symbols:following symbols:

(s) solid (l) liquid (g) gas (aq) aqueous, dissolved in (s) solid (l) liquid (g) gas (aq) aqueous, dissolved in waterwater

Balancing Chemical EquationsBalancing Chemical Equations

Add Add coefficientscoefficients to make sure you to make sure you have the same number of each atom have the same number of each atom on either side of the equation.on either side of the equation.

Identities of the compounds must Identities of the compounds must never be changed when balancing. never be changed when balancing. YOU CAN NEVER CHANGE A YOU CAN NEVER CHANGE A SUBSCRIPT IN A FORMULA!!!!!SUBSCRIPT IN A FORMULA!!!!!

Most chemical equations can be Most chemical equations can be balanced by trial and error.balanced by trial and error.

STEPSSTEPS – –

1.1. Write the unbalanced equation, making sure the Write the unbalanced equation, making sure the formulas of the compounds are correct.formulas of the compounds are correct.

2.2. Don’t forget the Don’t forget the diatomicsdiatomics – BrINClHOF if they appear by – BrINClHOF if they appear by themselves they must be written as Brthemselves they must be written as Br22, I, I22, N, N22, Cl, Cl22, H, H22, , OO22, F, F22

3.3. Use Use coefficientscoefficients in front of each substance to balance. in front of each substance to balance. The coefficient, 1, is never written.The coefficient, 1, is never written.

4.4. The best balanced equation is the one with the The best balanced equation is the one with the smallestsmallest ratio of coefficients.ratio of coefficients.

5.5. DOUBLE CHECK YOUR WORK!!!!DOUBLE CHECK YOUR WORK!!!!HINTS : 1) Make odd numbers of atoms even.HINTS : 1) Make odd numbers of atoms even.

2) Balance oxygen and hydrogen last.2) Balance oxygen and hydrogen last.3) If a polyatomic ion does not change count it as 3) If a polyatomic ion does not change count it as

a groupa group

Examples – Examples –

1.1. Reaction of hydrogen gas and Reaction of hydrogen gas and oxygen gas to form liquid water.oxygen gas to form liquid water.

2.2. Liquid ethanol, CLiquid ethanol, C22HH55OH, reacts with OH, reacts with oxygen gas to produce carbon oxygen gas to produce carbon dioxide gas and water vapor.dioxide gas and water vapor.

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

C3H5OH (g) + 3 O2 (g) 2 CO2 (g) + 3 H2O

(g)

3. Solid potassium reacts with liquid water 3. Solid potassium reacts with liquid water to form hydrogen gas and potassium to form hydrogen gas and potassium hydroxide that dissolves in water.hydroxide that dissolves in water.

LEARNING CHECK: Nitrogen trihydride gas LEARNING CHECK: Nitrogen trihydride gas reacts with oxygen gas to produce reacts with oxygen gas to produce nitrogen monoxide gas and water nitrogen monoxide gas and water vapor.vapor.

2 K (s) + 2 H2O (l) H2 (g) + 2 KOH (aq)

4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (g)

Examples:Examples:1)1) CC33HH8(g)8(g) + O + O2(g)2(g) CO CO2(g) 2(g) + H+ H22OO(g)(g)

2)2) NHNH44NONO2(s)2(s) N N2(g)2(g) + H + H22OO(g)(g)

3)3) NONO(g)(g) N N22OO(g)(g) + NO + NO2(g)2(g)

C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(g)

NH4NO2(s) N2(g) + 2 H2O(g)

3 NO(g) N2O(g) + NO2(g)

LEARNING CHECK: LEARNING CHECK:

HNOHNO3(aq)3(aq) NO NO2(g)2(g) + H + H22OO(l)(l) + O + O2(g)2(g)

MgMg(s)(s) + H + H22OO(l)(l) Mg(OH) Mg(OH)2(s) 2(s) + H + H2(g)2(g)

4 HNO3(aq) 4 NO2(g) + 2 H2O(l) + O2(g)

Mg(s) + 2 H2O(l) Mg(OH)2(s) + H2(g)

1. Soluble solid1. Soluble solid – readily dissolves in – readily dissolves in water water

2. Insoluble2. Insoluble and and slightly solubleslightly soluble solid solid – a solid where such a tiny amount – a solid where such a tiny amount dissolves in water that it is dissolves in water that it is undetectable to the naked eyeundetectable to the naked eye

3.3. Solubility is temperature dependent Solubility is temperature dependent

State is aqueous - (aq)

State is solid - (s)

Predicting States of Predicting States of SubstancesSubstances

States of reactants can be manipulated

Solubility RulesSolubility Rules (on snoopy sheet)(on snoopy sheet)

Ex. Predict whether the Ex. Predict whether the following following substances are substances are soluble or insoluble.soluble or insoluble.

AgNO3

Al(OH)3

Cu3PO4

Li2CO3

ZnSO4

(aq)

(aq)

(aq)

(s)

(s)

Solubility RulesMainly water soluble (aq)All nitrates are soluble.All acetates are soluble.All chlorates are soluble.All chlorides are soluble except AgCl, Hg2Cl2,

and PbCl2All bromides are soluble except AgBr, Hg2Br2,

PbBr2, and HgBr2

All iodides are soluble except AgI, Hg2I2, PbI2, and HgI2

All sulfates are soluble except CaSO4, SrSO4, BaSO4, PbSO4, Hg2SO4, and Ag2SO4

Mainly water insoluble (s)All sulfides are insoluble except those of 1A

and 2A elements and (NH4)2SAll carbonates are insoluble except those of

1A and (NH4)2CO3

All phosphates are insoluble except those of 1A and (NH4)3PO4

All hydroxides are insoluble except those of 1A, Ba(OH)2, Sr(OH)2 and Ca(OH)2

Learning CheckLearning Check

Try these: Determine if the following Try these: Determine if the following are AQUEOUS or SOLIDare AQUEOUS or SOLID

1. lead (II) nitrate1. lead (II) nitrate

2. potassium sulfide2. potassium sulfide

3. barium hydroxide3. barium hydroxide

4. ammonium carbonate4. ammonium carbonate Turn to your neighbor and compare Turn to your neighbor and compare

answersanswers

solid

aqueous

aqueous

aqueous

Special RulesSpecial Rules

1. Acids are aqueous2. Most metal oxides are solids3. Most non-metal oxides are gases

4. Liquids: Hg & Br2 Gases: H2, N2, O2, F2, Cl2 and Noble Gases

Solid: all other elements5. State (l) is reserved for pure liquids – H2O, and some hydrocarbons

Learning CheckLearning Check

Determine the state:Determine the state:1. lead(II) phosphate1. lead(II) phosphate

2. magnesium oxide2. magnesium oxide

3. nickel3. nickel

4. dinitrogen monoxide4. dinitrogen monoxide

5. chlorine5. chlorine

6. sulfuric acid6. sulfuric acid

7. sodium sulfide7. sodium sulfide

solid

solid

solid

gas

gas

aqueous

aqueous