14 reactions 1 - Chemistry...

ReactionsChapter 3

CombustionChapter 4 Reactions

DecompositionCombination

Exchange reactions (Metathesis)• Formation of a precipitate• Formation of a gasFormation of a gas• Formation of a week or non-

electrolyte

Single Displacement Reactions• Redox reactions• Oxidation numbers

Mary J. Bojan Chem 110 1

Balancing Equations

Law of conservation of mass: matter cannot be lost in anymatter cannot be lost in any

chemical reaction


Patterns of reactivity

• (Complete) Combustion reactions (Chapter 3)

Know how to balance a chemical reaction

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

• Combination reactions (Chapter 3)• Combination reactions (Chapter 3)2Mg(s) + O2() 2MgO(s)

(C )• Decomposition reactions (Chapter 3)PbCO3(s) PbO(s) + CO2(g)


Write balanced reactions for

The combustion of ethanol CH3CH2OH

The decomposition of lead carbonate PbCO3The decomposition of lead carbonate PbCO3

The combination of nitrogen and hydrogen to form ammonia (NH3)


Patterns of reactivityK h t b l h i l ti

• Exchange reactions (Chapter 4)P i it ti

Know how to balance a chemical reaction

PrecipitationPb(NO3)2(aq) + 2KI(aq) PbI(s) + 2KNO3(aq)

NeutralizationNaOH(aq) + HCl(aq) NaCl(aq) + H2O()

Gas formation2HCl(aq) + Na2S(aq) H2S(g) + 2NaCl(aq)

• Single displacement reactions (Chapter 4)2Ca(s) + O2(g) 2CaO(s)

Mary J. Bojan Chem 110

( ) 2(g) ( )

5

Exchange reaction(Double Displacement)(Double Displacement)

Exchange positive ions to get productsAD + XZ AZ + XD

Example:

R t t Pb(NO ) KIReactants: Pb(NO3)2 + KI

Balance the reaction.

D thi h ? TRY!Does anything happen? TRY!

Do you have to do the reaction to know?


y

6

Metathesis Reactions(Double Displacement)(Double Displacement)

Given reactants: exchange positive ions to get productsproducts

Requires a driving force (otherwise nothing happens)

D i i FDriving Forces

1. Precipitate forms2. Weak or nonelectrolyte forms 3. Gas forms

How do you know what is happening?

Net Ionic EquationMary J. Bojan Chem 110

Net Ionic Equation 7

Precipitation ReactionMix silver nitrate and sodium chloride.

What happens?

Molecular Equation

Ionic Equation

Spectator ions:

Net Ionic Equation


SOLUBILITY RULES FOR COMMON IONIC COMPOUNDS IN WATER

1. Almost all ammonium and alkali metal salts are soluble.

2. Most nitrates, acetates, chlorides, bromides, and sulfates are soluble.Exceptions: silver halidesp

sulfates of Ca,Ba,Pb,Ag

3 Most sulfides carbonates phosphates and hydroxides3. Most sulfides, carbonates, phosphates and hydroxides are insoluble.Exceptions: alkali salts

ammonium salts. (See #1 above.)

See Table 4.1 of Brown, LeMay, and Bursten for a more comprehensive listing.


Formation of Weak or Nonelectrolyte(neutralization reaction)

Acid + base salt + waterMolecular Equation

Ionic EquationIonic Equation

Spectator ions:

Net Ionic Equation


PracticeWhat is the net ionic equation for the reaction between sodium hydroxide and acetic acid?

What is the net ionic equation for the reaction between sodium chloride and potassium iodide?chloride and potassium iodide?


GAS FORMATIONDi t d ti f CO H S NO SO

Example:

• Direct production of a gas CO2, H2S, NO2, SO2• Production of weak acid which decomposes.

Molecular EquationNaHCO3(aq) + HCl(aq) H2CO3(aq) + NaCl(aq)

CO2(g) + H2O(l)

Ionic EquationNa+(aq) + HCO3

(aq) + H+(aq) + Cl(aq) H2CO3 (aq)+ Na+(aq) + Cl(aq) Na (aq) HCO3 (aq) H (aq) Cl (aq) H2CO3 (aq) Na (aq) Cl (aq)

Na+(aq) + Cl(aq) + CO2(g) + H2O(l)Net Ionic EquationNet Ionic Equation

H+(aq) + HCO3(aq) CO2(g)+ H2O(l)


Single Displacement reactions(Oxidation-Reduction)(Oxidation Reduction)

Zn(s) + CuSO4(aq) ZnSO4(aq) +Cu(s)

What is oxidized? What is reduced?

What is the oxidizing agent? What is the reducing agent?

Ionic equation:

Net ionic equationNet ionic equation


Rules for determining Oxidation States1. Oxidation state of atom in elemental form is zero.1. Oxidation state of atom in elemental form is zero.

e.g. Cl2 O2 P4 C(s) S8

2. The oxidation number of a monatomic ion equals its charge.3. Some elements have “common” oxidation numbers that can be used as

reference in determining the oxidation numbers of other atoms in thereference in determining the oxidation numbers of other atoms in the compound.

Alkali metals +1Alkaline earth metals +2Fluorine –1Fluorine –1H usually +1

Hydrides: metal-H compounds (–1)O usually –2

peroxides (–1) & superoxides possibleperoxides (–1) & superoxides possibleCl, Br, I almost always –1

4. Sum of oxidation numbers is equal to overall charge of molecule or ion:• For a neutral compound the sum of oxidation numbers equals zero.• For a polyatomic ion the sum of the oxidation numbers is equal to theFor a polyatomic ion, the sum of the oxidation numbers is equal to the

charge on the ion.

5. Shared electrons are assigned to the more electronegative atom of the pair: more electronegative atom will have a negative oxidation number


more electronegative atom will have a negative oxidation number.

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ActivitySeriesTable 4.5Table 4.5

Will the metal element displace the atom from its compound in a reaction?

Na(s) + H2O(l)

Au(s) + H2O(g) ( ) 2 (g)

Zn(s) + AgNO3(aq)

Active metals (groups IA, IIA, Al) very reactive!

I ti (i t t l ) j l t l D t t dilInactive (inert metals): jewelry metals Do not react readily

Other metals in between


Reactions: StoichiometryReactions: Stoichiometry

• Solving problems involving Chemical reactions• Solving problems involving Chemical reactions• Limiting Reactants• Solution reactions

G h i• Gas phase reactions


Basics: before you start!Assume you know:• Avogadro’s number

i it!memorize it!• definition of mole• Formula weight (molar mass)g ( )• the following connections (or

conversions)gram molegram molegram molecules

• what is meant by:i i l f l

Use these along with the empirical formulamolecular formula

balanced chemical reaction to solve problems in chemistry


p y

How to solve problems• write the balanced chemical reaction (or process).

• make connections between experimentally measured properties and the balanced equation.

In other words:

Given information such as mass, volume, pressure and temperature how can one determine quantities oftemperature, how can one determine quantities of moles/molecules?


• Avogadro’s numberC t l l ( t ) t l

IMPORTANT CONNECTIONS

Connects molecules (or atoms) to molesConnects microscopic properties to macroscopic properties.

• Conservation of MassMass of Products = Mass of reactantsBalance the reaction

• Balanced Chemical EquationConnects moles (molecules) of reactants with moles (molecules) of productsRelated to conservation of Mass

• Formula weightConnects mass to molesConnects a property that can be measured (determined) experimentally to moles (or molecules) of substance given in the balanced reaction.

• Empirical FormulaTells relative number of atoms in a molecule


Obtained from %mass or molecular formula19

Problem Solving1 Write balanced chemical equation1. Write balanced chemical equation2. Make a table: Fill in given information3. Note connections between measured

titi d lquantities and moles

Mass molesM.W.

Volume (solutions)

molesconcentration

ideal gas lawP, V, T (gases)

molesideal gas law

4. Fill in table until you are able to solve the problem 5. Make sure your answer is REASONABLE6 TRY things


6. TRY things

20

Sample ProblemsSample ProblemsMethane reacts with water to produce hydrogen gas and carbon monoxide. If 8.0g of methane reacts with 9.0 g of water, howmonoxide. If 8.0g of methane reacts with 9.0 g of water, how many grams of hydrogen gas will be produced?


If a clean burning engine burns 1 gallon of gasoline (assume a c ea bu g e g e bu s ga o o gaso e (assu ethis is 2600 g of octane), how many kg of CO2 will it produce? Octane is C8H18

Assume:• Gasoline is all octane• Density of octane = 0.692g/ml

1 l 3 79 l 3790 l• 1 gal = 3.79 l = 3790 ml• 3790ml x 0.692g/ml = 2622.68 g 2600 g of octane


You try!If 36.6 g of C2H5OH reacts with 63.8 g of O2, how many grams of CO2 will be produced?

1. 26.0g2 43 2g2. 43.2g3. 58.5 g4 70 4 g4. 70.4 g5. 100.4g


Limiting reagentLimiting reagent

• Reactant that is used up first• Determines the amount of product• Must start with a balanced reaction

BE SURE TO TEST BOTH REACTANTS


Problem Solving with solutions: TitrationMolarity is the connection between moles and volume in

solutions.

If 46.0ml of 0.100M NaOH is needed to neutralize 20.0 ml of a H SO solution what is the concentration of H SO ?


of a H2SO4 solution what is the concentration of H2SO4?25

Problem Solving with gasesFor a gas, PV=nRT is the link between the # of moles (n) and the experimental quantities P,V, and T of gas.Example: How many L of N at 735 mm Hg and 26C are

di id i i b

Example: How many L of N2 at 735 mm Hg and 26C are produced from 126g of NaN3 (sodium azide)?

sodium azide gas in an airbag2NaN3(s) 2Na(s) + 3 N2(g)

P,V,Tmass

idealMWgas law

molesmolesMary J. Bojan Chem 110

molesmoles26

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