CHAPTER 3A & 4A

Stoichiometry and Reactions

Chemical Reactions

Chemical equation – a representation of a chemical reaction.

Reactants – the starting chemicals.

Products – the ending chemicals.

CH4 + O2 → CO2 + H2O

Reactant Product

Conservation of matter – in a chemical reaction, atoms are neither created nor destroyed.

Physical States

The state of the compound can be stated in the reaction equation using the following symbols.

Solid (s)Liquid (l)Gas (g)Dissolved in water (aq)

Balancing Equations

C(s) + O2(g) → CO2(g) Reactants Products

All atoms present in the reactants must be accounted for among the products

C-1 → C-1 O-2 O-2

Balancing Rules

Read the description and write the formulas for the reactants and products.

Write the unbalanced formula.

Balance the equation starting with the most complicated molecule. Remember to not change the formula of the chemicals.

Check to confirm balance.

Balancing Equaitons

Methane reacts with oxygen to produce carbon dioxide and water.

CH4(g) + O2(g) → CO2(g) + H2O(l)

C-1 C-1 H-4 H-2 O-2 O-3

Balancing equations

K + H2O → H2 + KOH

NH3 + O2 → NO + H20

SiO2 + HF → SiF4 + H2O

CaC2 + H2O → Ca(OH)2 + C2H2

Balancing Equations

Hydrogen gas combines with oxygen gas to produce water.

Sodium metal combines with water to produce sodium hydroxide liquid and hydrogen gas.

Aluminum solid combines with chlorine gas to produce aluminum chloride solid.

Hydrochloric acid (aqueous solution) combines with calcium carbonate solid to form calcium chloride, carbon dioxide gas and water.

Reaction Types

Composition (synthesis)

Decomposition

Single Replacement

Double replacement (precipitation)

Acid/Base

Reaction Types

Composition reaction – a reaction that combines substances to form a single substance.

A + B → C

2H2 + O2 → 2H2O

C + O2 → CO2

2Na + Cl2 → 2NaCl

Reaction Types

Decomposition reaction – a reaction in which a compound is broken down into two or more simpler substances.

AB → A + B

2H2O → 2H2 + O2

2NaCl → 2Na + 2ClCaCO3 → CaO + CO2

Reaction Types

Single replacement reaction – a reaction in which one element takes the place of another element

A + BC → B + AC

Cu + 2AgNO3 → Cu(NO3)2 + Ag

2K + 2H2O → H2 + 2KOH

Reaction Types

Double replacement reaction – a reaction in which two different compounds exchange positive ions and form two new compounds.

AB + CD → AD + CB

Pb(NO3)2 + KI → PbI2 + 2KNO3

CaCO3 + 2HCl → CaCl2 + H2CO3

Reaction Types

2K + Cl2 → 2KCl

Fe2O3 + 2Al → Al2O3 + 2Fe

2Mg + O2 → 2MgO

HNO3 + NaOH → H2O + NaNO3

KBr + AgNO3 → AgBr + KNO3

PbO2 → Pb + O2

Single Replacement ReactionIf the free metal is higher on the metal

activity table than a metal in solution then the free metal will exchange places with the metal in solution.

Ex. Zn + HBr → NiCl2 + K →

Cu + HCl →

Double Replacement Reaction Prediction

Metathesis reactions are driven by three "driving forces."

1) A product is a precipitate2) A product is a gas3) A product is a weak or non-electrolyte We reduced these to;1) A product is an ionic precipitate2) A product is a molecular, non-strong acid

Double Replacement

The solubility table is used to determine if an ionic precipitate is formed from the reactants.

Ex. K2S + Fe(NO3)2

Na2SO4 + BaCl2HCl + MgS KI + NH4NO3

Double Replacement Reaction

Molecular equation – equation in which the complete formulas of all reactants and products are given.

Complete ionic equation – equation in which all substances that are strong electrolytes are represented as ions.

Spectator ions – ions which do not participate in the reaction.

Net ionic equation – equation in which the spectator ions are not represented only the components involved in the reaction.

Double Replacement Reaction

For each of the following reactions, write the balanced molecular equation, the balanced complete ionic equation, and the balanced net ionic equation.

Silver nitrate and sodium chromateAgNO3 + NaCrO4

Nickel(II) nitrate and potassium carbonate

Ni(NO3)2 + K2CO3

Electrolytes

Strong Electrolytes – ionic compounds that total dissociate in water and conduct electricity.

Weak electrolytes – molecular acids that can totally or partially dissociate in water.

Non electrolytes – molecular compounds that do not dissociate in water so do not conduct electricity.

Acid/Base Reactions

Acids – substances that ionize in aqueous solutions to form hydrogen ions.

H2SO4(aq) → H+(aq) + HSO4-(aq)

Strong acids – strong electrolytes

Bases – substances that ionize in aqueous solutions to form hydroxide ions.

NaOH(s) → Na+(aq) + OH-(aq)

Strong Acids/Bases

Strong Acids HCl –hydrochloric acid HBr – hydrobromic acid HI – hydroiodic acid HClO3 – chloric acid HClO4 – prechloric acid HNO3 – nitric acid H2SO4 – sulfuric acid

Strong Bases Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Group 2a metal hydroxides (Ca(OH)2, Sr(OH)2, Ba(OH)2)

Acid/Base Reactions

Acid/Base reactions result in the formation of a salt and water

Ex. Write the balanced molecular, balanced complete ionic, and balanced net ionic equations for the reaction of aqueous hydrobromic acid and aqueous sodium hydroxide.

Acid/Base Reaction

Write the balanced molecular, balanced complete ionic, and balanced net ionic equations for the reaction of aqueous sulfuric acid and aqueous potassium hydroxide.