Chapter 8 Chemical Equations and Reactions

(NH4)2Cr2O7 (s)  N2(g) + Cr2O3 (s) + 4H2O(g) Chemical Equations Represents, w/ symbols & formulas, the reactants & products in a chemical reaction Requirements Must represent the known facts Must contain correct formulas Must satisfy the law of conservation (NH4)2Cr2O7 (s)  N2(g) + Cr2O3 (s) + 4H2O(g)

Indication of a Chemical Reaction Production of light or heat. Production of gas or smoke. Formation of a precipitate (ppt). Color change.

Diatomic Molecules Elements that normally exist as diatomic molecules. H2, N2, O2, F2, Cl2, Br2 and I2

Word & Formula Equations Word Equation – chemical equation represented w/ words Methane Gas + Oxygen Gas  Carbon Dioxide Gas + Water Vapor Formula Equation – chemical equation represented w/ formulas & symbols CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g) Coefficient Small whole number used to balance the equation

Common Symbols in Equations Explanation  “Yields” indicates result of reaction  Reversible Reaction (s) Reactant or Product in solid state  Precipitate (alternative for solid) (l) Reactant or Product in liquid state (aq) Reactant or Product in aqueous solution (dissolved in water) (g) Reactant or Product in gas  Gaseous Product (alternative for gas) Reactants are Heated

Practice Solid Sodium hydroxide reacts with nitric acid in a solution to produce sodium nitrate and water when heated. Write a word and formula equation for this sentence.

2nd Practice Equation Aluminum sulfate and calcium hydroxide are used in a water purification process. When added to water they dissolve and react to produce two insoluble (solid) products, aluminum hydroxide and calcium sulfate. Write a word and formula equation representing this reaction.

Silver Reactions

Thermite Reaction Thermite

Balancing Equations Mass of Reactants must equal Mass of Products No Atoms can be lost during the reaction

8.2 Types of Chemical Equations Synthesis (Composition) A + X  AX Decomposition AX  A + X Single Replacement A + BX  AX + B Double Replacement AX + BY  AY + BX Combustion CxHy + O2  CO2 + H2O

Synthesis Reactions A + X  AX Formation of: Binary Ionic Compounds Binary Molecular Compounds Formation of Metal Hydroxides Oxyacids

Reaction of Metals with Nonmetals Example 1 Mg + O2  Example 2 Fe + O2  Example 3 Na + Cl2 

Reaction of two Nonmetals Reactions are dependant upon the amounts of each reactant available. Example 1 C + O2  Example 2 S + O2  Example 3(limited amount of Oxygen)

Synthesis Reactions of Metal Oxides w/ Water MxOy + H2O  M (OH)y metal oxide + water  metal hydroxide Example 1 CaO + H2O 

Synthesis Reactions of Nonmetal Oxides w/ Water NOTE: The acid produce has the nonmetal in the same oxidation state as it was in the nonmetal oxide. NMxOy + H2O  HxNMOy nonmetal oxide + water  Oxyacid Example 1 SO3 + H2O  Example 2 N2O5 + H2O 

Decomposition AX  A + X Binary Compounds Metal Carbonates Metal Hydroxides Metal Chlorates Oxyacids

Decomposition of Binary Compounds AX  A + X Example 1 HgO  Example 2 H2O 

Decomposition of Metal Carbonates MCO3  MO + CO2 metal carbonate  metal oxide + carbon dioxide Example 1 CaCO3  Poo Poo and Pee Pee

Decomposition of Metal Hydroxides MOH  MO + H2O Metal hydroxide  metal oxide + water Example 1 Ca(OH)2 

Decomposition of Metal Chlorates M(ClO3)  MCl + O2 metal chlorate  metal chloride + oxygen Example 1 KClO3 

Decomposition of Acids Acid  Nonmetal Oxides + H2O Nonmetals in the nonmetal oxides will have the same oxidation state as it did in the acid. Example 1 H2SO4  Example 2 HNO2 

Single Replacement Reactions A + BX  AX + B Y + BX  BY + X Replacement of a Metal by another Metal Al + Fe(NO3)3  Replacement of Hydrogen in Water by a Metal Na + H2O  Must check the activity series to make sure the lone element has a greater activity than the element in the compound.

Can react with steam and acids, replacing the hydrogen. lithium potassium barium strontium calcium sodium magnesium aluminum zinc chromium iron cadmium cobalt nickel tin lead Hydrogen antimony arsenic bismuth copper mercury silver palladium platinum gold Can react with cold water and acids, replacing hydrogen. Will form Metal Hydroxide and Hydrogen when added to water. Can react with steam and acids, replacing the hydrogen. Can react with acids, replacing the hydrogen. React with oxygen, forming oxides. Fairly unreactive. Form oxides only indirectly.

Single Replacement Reactions Replacement of Hydrogen in an Acid by a Metal Mg + HCl  Replacement of Halogens Cl2 + KBr 

Double Replacement Reactions AX + BY  AY + BX Positive Ions (cations) in Both Compounds Switch Places Positive Ions are Written First Pb(NO3)2 + KI  HCl + NaOH 

Combustion : Complete CxHy(Oz) + O2  CO2 + H2O C2H6 + O2  C6H6O2 + O2  Combustion InComplete CxHy(Oz) + O2  CO + H2O